Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
359 KiB
Domain XML format
This section describes the XML format used to represent domains, there are variations on the format based on the kind of domains run and the options used to launch them. For hypervisor specific details consult the driver docs
Element and attribute overview
The root element required for all virtual machines is named domain
. It has two attributes, the type
specifies the hypervisor used for running the domain. The allowed values are driver specific, but include "xen", "kvm", "hvf" (since 8.1.0 and QEMU 2.12), "qemu" and "lxc". The second attribute is id
which is a unique integer identifier for the running guest machine. Inactive machines have no id value.
General metadata
<domain type='kvm' id='1'>
<name>MyGuest</name>
<uuid>4dea22b3-1d52-d8f3-2516-782e98ab3fa0</uuid>
<genid>43dc0cf8-809b-4adb-9bea-a9abb5f3d90e</genid>
<title>A short description - title - of the domain</title>
<description>Some human readable description</description>
<metadata>
<app1:foo xmlns:app1="http://app1.org/app1/">..</app1:foo>
<app2:bar xmlns:app2="http://app1.org/app2/">..</app2:bar>
</metadata>
...
name
The content of the
name
element provides a short name for the virtual machine. This name should consist only of alphanumeric characters and is required to be unique within the scope of a single host. It is often used to form the filename for storing the persistent configuration file. Since 0.0.1uuid
The content of the
uuid
element provides a globally unique identifier for the virtual machine. The format must be RFC 4122 compliant, eg3e3fce45-4f53-4fa7-bb32-11f34168b82b
. If omitted when defining/creating a new machine, a random UUID is generated. It is also possible to provide the UUID via a SMBIOS System Information specification. Since 0.0.1, sysinfo since 0.8.7genid
Since 4.4.0 , the
genid
element can be used to add a Virtual Machine Generation ID which exposes a 128-bit, cryptographically random, integer value identifier, referred to as a Globally Unique Identifier (GUID) using the same format as theuuid
. The value is used to help notify the guest operating system when the virtual machine is re-executing something that has already executed before, such as:- VM starts executing a snapshot
- VM is recovered from backup
- VM is failover in a disaster recovery environment
- VM is imported, copied, or cloned
The guest operating system notices the change and is then able to react as appropriate by marking its copies of distributed databases as dirty, re-initializing its random number generator, etc.
The libvirt XML parser will accept both a provided GUID value or just <genid/> in which case a GUID will be generated and saved in the XML. For the transitions such as above, libvirt will change the GUID before re-executing.
title
The optional element
title
provides space for a short description of the domain. The title should not contain any newlines. Since 0.9.10 .description
The content of the
description
element provides a human readable description of the virtual machine. This data is not used by libvirt in any way, it can contain any information the user wants. Since 0.7.2metadata
The
metadata
node can be used by applications to store custom metadata in the form of XML nodes/trees. Applications must use custom namespaces on their XML nodes/trees, with only one top-level element per namespace (if the application needs structure, they should have sub-elements to their namespace element). Since 0.9.10
Operating system booting
There are a number of different ways to boot virtual machines each with their own pros and cons.
BIOS bootloader
Booting via the BIOS is available for hypervisors supporting full virtualization. In this case the BIOS has a boot order priority (floppy, harddisk, cdrom, network) determining where to obtain/find the boot image.
<!-- Xen with fullvirt loader -->
...
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<boot dev='hd'/>
</os>
...
<!-- QEMU with default firmware, serial console and SMBIOS -->
...
<os>
<type>hvm</type>
<boot dev='cdrom'/>
<bootmenu enable='yes' timeout='3000'/>
<smbios mode='sysinfo'/>
<bios useserial='yes' rebootTimeout='0'/>
</os>
...
<!-- QEMU with UEFI manual firmware and secure boot -->
...
<os>
<type>hvm</type>
<loader readonly='yes' secure='yes' type='pflash'>/usr/share/OVMF/OVMF_CODE.fd</loader>
<nvram template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram>
<boot dev='hd'/>
</os>
...
<!-- QEMU with automatic UEFI firmware and secure boot -->
...
<os firmware='efi'>
<type>hvm</type>
<loader secure='yes'/>
<boot dev='hd'/>
</os>
...
firmware
The
firmware
attribute allows management applications to automatically fill<loader/>
and<nvram/>
elements and possibly enable some features required by selected firmware. Accepted values arebios
andefi
. The selection process scans for files describing installed firmware images in specified location and uses the most specific one which fulfils domain requirements. The locations in order of preference (from generic to most specific one) are:/usr/share/qemu/firmware
/etc/qemu/firmware
$XDG_CONFIG_HOME/qemu/firmware
For more information refer to firmware metadata specification as described in
docs/interop/firmware.json
in QEMU repository. Regular users do not need to bother. Since 5.2.0 (QEMU and KVM only) For VMware guests, this is set toefi
when the guest uses UEFI, and it is not set when using BIOS. Since 5.3.0 (VMware ESX and Workstation/Player)type
The content of the
type
element specifies the type of operating system to be booted in the virtual machine.hvm
indicates that the OS is one designed to run on bare metal, so requires full virtualization.linux
(badly named!) refers to an OS that supports the Xen 3 hypervisor guest ABI. There are also two optional attributes,arch
specifying the CPU architecture to virtualization, andmachine
referring to the machine type. The Capabilities XML provides details on allowed values for these. Ifarch
is omitted then for most hypervisor drivers, the host native arch will be chosen. For thetest
,ESX
andVMWare
hypervisor drivers, however, thei686
arch will always be chosen even on anx86_64
host. Since 0.0.1firmware
Since 7.2.0 QEMU/KVM only
When using firmware auto-selection there are different features enabled in the firmwares. The list of features can be used to limit what firmware should be automatically selected for the VM. The list of features can be specified using zero or more
feature
elements. Libvirt will take into consideration only the listed features and ignore the rest when selecting the firmware.feature
The list of mandatory attributes:
enabled
(accepted values areyes
andno
) is used to tell libvirt if the feature must be enabled or not in the automatically selected firmwarename
the name of the feature, the list of the features:enrolled-keys
whether the selected nvram template has default certificate enrolled. Firmware with Secure Boot feature but without enrolled keys will successfully boot non-signed binaries as well. Valid only for firmwares with Secure Boot feature.secure-boot
whether the firmware implements UEFI Secure boot feature.
loader
The optional
loader
tag refers to a firmware blob, which is specified by absolute path, used to assist the domain creation process. It is used by Xen fully virtualized domains as well as setting the QEMU BIOS file path for QEMU/KVM domains. Xen since 0.1.0, QEMU/KVM since 0.9.12 Then, since 1.2.8 it's possible for the element to have two optional attributes:readonly
(accepted values areyes
andno
) to reflect the fact that the image should be writable or read-only. The second attributetype
accepts valuesrom
andpflash
. It tells the hypervisor where in the guest memory the file should be mapped. For instance, if the loader path points to an UEFI image,type
should bepflash
. Moreover, some firmwares may implement the Secure boot feature. Attributesecure
can be used to tell the hypervisor that the firmware is capable of Secure Boot feature. It cannot be used to enable or disable the feature itself in the firmware. Since 2.1.0nvram
Some UEFI firmwares may want to use a non-volatile memory to store some variables. In the host, this is represented as a file and the absolute path to the file is stored in this element. Moreover, when the domain is started up libvirt copies so called master NVRAM store file defined in
qemu.conf
. If needed, thetemplate
attribute can be used to per domain override map of master NVRAM stores from the config file. Note, that for transient domains if the NVRAM file has been created by libvirt it is left behind and it is management application's responsibility to save and remove file (if needed to be persistent). Since 1.2.8boot
The
dev
attribute takes one of the values "fd", "hd", "cdrom" or "network" and is used to specify the next boot device to consider. Theboot
element can be repeated multiple times to setup a priority list of boot devices to try in turn. Multiple devices of the same type are sorted according to their targets while preserving the order of buses. After defining the domain, its XML configuration returned by libvirt (through virDomainGetXMLDesc) lists devices in the sorted order. Once sorted, the first device is marked as bootable. Thus, e.g., a domain configured to boot from "hd" with vdb, hda, vda, and hdc disks assigned to it will boot from vda (the sorted list is vda, vdb, hda, hdc). Similar domain with hdc, vda, vdb, and hda disks will boot from hda (sorted disks are: hda, hdc, vda, vdb). It can be tricky to configure in the desired way, which is why per-device boot elements (see Hard drives, floppy disks, CDROMs, Network interfaces, and Host device assignment sections below) were introduced and they are the preferred way providing full control over booting order. Theboot
element and per-device boot elements are mutually exclusive. Since 0.1.3, per-device boot since 0.8.8smbios
How to populate SMBIOS information visible in the guest. The
mode
attribute must be specified, and is either "emulate" (let the hypervisor generate all values), "host" (copy all of Block 0 and Block 1, except for the UUID, from the host's SMBIOS values; the virConnectGetSysinfo call can be used to see what values are copied), or "sysinfo" (use the values in the SMBIOS System Information element). If not specified, the hypervisor default is used. Since 0.8.7
Up till here the BIOS/UEFI configuration knobs are generic enough to be implemented by majority (if not all) firmwares out there. However, from now on not every single setting makes sense to all firmwares. For instance, rebootTimeout
doesn't make sense for UEFI, useserial
might not be usable with a BIOS firmware that doesn't produce any output onto serial line, etc. Moreover, firmwares don't usually export their capabilities for libvirt (or users) to check. And the set of their capabilities can change with every new release. Hence users are advised to try the settings they use before relying on them in production.
bootmenu
Whether or not to enable an interactive boot menu prompt on guest startup. The
enable
attribute can be either "yes" or "no". If not specified, the hypervisor default is used. Since 0.8.3 Additional attributetimeout
takes the number of milliseconds the boot menu should wait until it times out. Allowed values are numbers in range [0, 65535] inclusive and it is ignored unlessenable
is set to "yes". Since 1.2.8bios
This element has attribute
useserial
with possible valuesyes
orno
. It enables or disables Serial Graphics Adapter which allows users to see BIOS messages on a serial port. Therefore, one needs to have Serial port defined. Since 0.9.4 . Since 0.10.2 (QEMU only) there is another attribute,rebootTimeout
that controls whether and after how long the guest should start booting again in case the boot fails (according to BIOS). The value is in milliseconds with maximum of65535
and special value-1
disables the reboot.
Host bootloader
Hypervisors employing paravirtualization do not usually emulate a BIOS, and instead the host is responsible to kicking off the operating system boot. This may use a pseudo-bootloader in the host to provide an interface to choose a kernel for the guest. An example is pygrub
with Xen. The Bhyve hypervisor also uses a host bootloader, either bhyveload
or grub-bhyve
.
...
<bootloader>/usr/bin/pygrub</bootloader>
<bootloader_args>--append single</bootloader_args>
...
bootloader
The content of the
bootloader
element provides a fully qualified path to the bootloader executable in the host OS. This bootloader will be run to choose which kernel to boot. The required output of the bootloader is dependent on the hypervisor in use. Since 0.1.0bootloader_args
The optional
bootloader_args
element allows command line arguments to be passed to the bootloader. Since 0.2.3
Direct kernel boot
When installing a new guest OS it is often useful to boot directly from a kernel and initrd stored in the host OS, allowing command line arguments to be passed directly to the installer. This capability is usually available for both para and full virtualized guests.
...
<os>
<type>hvm</type>
<loader>/usr/lib/xen/boot/hvmloader</loader>
<kernel>/root/f8-i386-vmlinuz</kernel>
<initrd>/root/f8-i386-initrd</initrd>
<cmdline>console=ttyS0 ks=http://example.com/f8-i386/os/</cmdline>
<dtb>/root/ppc.dtb</dtb>
<acpi>
<table type='slic'>/path/to/slic.dat</table>
</acpi>
</os>
...
type
This element has the same semantics as described earlier in the BIOS bootloader section.
loader
This element has the same semantics as described earlier in the BIOS bootloader section.
kernel
The contents of this element specify the fully-qualified path to the kernel image in the host OS.
initrd
The contents of this element specify the fully-qualified path to the (optional) ramdisk image in the host OS.
cmdline
The contents of this element specify arguments to be passed to the kernel (or installer) at boot time. This is often used to specify an alternate primary console (eg serial port), or the installation media source / kickstart file
dtb
The contents of this element specify the fully-qualified path to the (optional) device tree binary (dtb) image in the host OS. Since 1.0.4
acpi
The
table
element contains a fully-qualified path to the ACPI table. Thetype
attribute contains the ACPI table type (currently onlyslic
is supported) Since 1.3.5 (QEMU) Since 5.9.0 (Xen)
Container boot
When booting a domain using container based virtualization, instead of a kernel / boot image, a path to the init binary is required, using the init
element. By default this will be launched with no arguments. To specify the initial argv, use the initarg
element, repeated as many time as is required. The cmdline
element, if set will be used to provide an equivalent to /proc/cmdline
but will not affect init argv.
To set environment variables, use the initenv
element, one for each variable.
To set a custom work directory for the init, use the initdir
element.
To run the init command as a given user or group, use the inituser
or initgroup
elements respectively. Both elements can be provided either a user (resp. group) id or a name. Prefixing the user or group id with a +
will force it to be considered like a numeric value. Without this, it will be first tried as a user or group name.
<os>
<type arch='x86_64'>exe</type>
<init>/bin/systemd</init>
<initarg>--unit</initarg>
<initarg>emergency.service</initarg>
<initenv name='MYENV'>some value</initenv>
<initdir>/my/custom/cwd</initdir>
<inituser>tester</inituser>
<initgroup>1000</initgroup>
</os>
If you want to enable user namespace, set the idmap
element. The uid
and gid
elements have three attributes:
start
First user ID in container. It must be '0'.
target
The first user ID in container will be mapped to this target user ID in host.
count
How many users in container are allowed to map to host's user.
<idmap>
<uid start='0' target='1000' count='10'/>
<gid start='0' target='1000' count='10'/>
</idmap>
SMBIOS System Information
Some hypervisors allow control over what system information is presented to the guest (for example, SMBIOS fields can be populated by a hypervisor and inspected via the dmidecode
command in the guest). The optional sysinfo
element covers all such categories of information. Since 0.8.7
...
<os>
<smbios mode='sysinfo'/>
...
</os>
<sysinfo type='smbios'>
<bios>
<entry name='vendor'>LENOVO</entry>
</bios>
<system>
<entry name='manufacturer'>Fedora</entry>
<entry name='product'>Virt-Manager</entry>
<entry name='version'>0.9.4</entry>
</system>
<baseBoard>
<entry name='manufacturer'>LENOVO</entry>
<entry name='product'>20BE0061MC</entry>
<entry name='version'>0B98401 Pro</entry>
<entry name='serial'>W1KS427111E</entry>
</baseBoard>
<chassis>
<entry name='manufacturer'>Dell Inc.</entry>
<entry name='version'>2.12</entry>
<entry name='serial'>65X0XF2</entry>
<entry name='asset'>40000101</entry>
<entry name='sku'>Type3Sku1</entry>
</chassis>
<oemStrings>
<entry>myappname:some arbitrary data</entry>
<entry>otherappname:more arbitrary data</entry>
</oemStrings>
</sysinfo>
<sysinfo type='fwcfg'>
<entry name='opt/com.example/name'>example value</entry>
<entry name='opt/com.coreos/config' file='/tmp/provision.ign'/>
</sysinfo>
...
The sysinfo
element has a mandatory attribute type
that determine the layout of sub-elements, with supported values of:
smbios
Sub-elements call out specific SMBIOS values, which will affect the guest if used in conjunction with the
smbios
sub-element of theos
element (see Operating system booting). Each sub-element ofsysinfo
names a SMBIOS block, and within those elements can be a list ofentry
elements that describe a field within the block. The following blocks and entries are recognized:bios
This is block 0 of SMBIOS, with entry names drawn from:
vendor
BIOS Vendor's Name
version
BIOS Version
date
BIOS release date. If supplied, is in either mm/dd/yy or mm/dd/yyyy format. If the year portion of the string is two digits, the year is assumed to be 19yy.
release
System BIOS Major and Minor release number values concatenated together as one string separated by a period, for example, 10.22.
system
This is block 1 of SMBIOS, with entry names drawn from:
manufacturer
Manufacturer of BIOS
product
Product Name
version
Version of the product
serial
Serial number
uuid
Universal Unique ID number. If this entry is provided alongside a top-level
uuid
element (see General metadata), then the two values must match.sku
SKU number to identify a particular configuration.
family
Identify the family a particular computer belongs to.
baseBoard
This is block 2 of SMBIOS. This element can be repeated multiple times to describe all the base boards; however, not all hypervisors necessarily support the repetition. The element can have the following children:
manufacturer
Manufacturer of BIOS
product
Product Name
version
Version of the product
serial
Serial number
asset
Asset tag
location
Location in chassis
NB: Incorrectly supplied entries for the
bios
,system
orbaseBoard
blocks will be ignored without error. Other thanuuid
validation anddate
format checking, all values are passed as strings to the hypervisor driver.chassis
Since 4.1.0, this is block 3 of SMBIOS, with entry names drawn from:
manufacturer
Manufacturer of Chassis
version
Version of the Chassis
serial
Serial number
asset
Asset tag
sku
SKU number
oemStrings
This is block 11 of SMBIOS. This element should appear once and can have multiple
entry
child elements, each providing arbitrary string data. There are no restrictions on what data can be provided in the entries, however, if the data is intended to be consumed by an application in the guest, it is recommended to use the application name as a prefix in the string. ( Since 4.1.0 )
fwcfg
Some hypervisors provide unified way to tweak how firmware configures itself, or may contain tables to be installed for the guest OS, for instance boot order, ACPI, SMBIOS, etc.
It even allows users to define their own config blobs. In case of QEMU, these then appear under domain's sysfs (if the guest kernel has FW_CFG_SYSFS config option enabled), under
/sys/firmware/qemu_fw_cfg
. Note, that these values apply regardless the<smbios/>
mode under<os/>
. Since 6.5.0Please note that because of limited number of data slots use of fwcfg is strongly discouraged and <oemStrings/> should be used instead.
<sysinfo type='fwcfg'> <entry name='opt/com.example/name'>example value</entry> <entry name='opt/com.example/config' file='/tmp/provision.ign'/> </sysinfo>
The
sysinfo
element can have multipleentry
child elements. Each element then has mandatoryname
attribute, which defines the name of the blob and must begin with"opt/"
and to avoid clashing with other names is advised to be in form"opt/$RFQDN/$name"
where$RFQDN
is a reverse fully qualified domain name you control. Then, the element can either contain the value (to set the blob value directly), orfile
attribute (to set the blob value from the file).
CPU Allocation
<domain>
...
<vcpu placement='static' cpuset="1-4,^3,6" current="1">2</vcpu>
<vcpus>
<vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
<vcpu id='1' enabled='no' hotpluggable='yes'/>
</vcpus>
...
</domain>
vcpu
The content of this element defines the maximum number of virtual CPUs allocated for the guest OS, which must be between 1 and the maximum supported by the hypervisor.
cpuset
The optional attribute
cpuset
is a comma-separated list of physical CPU numbers that domain process and virtual CPUs can be pinned to by default. (NB: The pinning policy of domain process and virtual CPUs can be specified separately bycputune
. If the attributeemulatorpin
ofcputune
is specified, thecpuset
specified byvcpu
here will be ignored. Similarly, for virtual CPUs which have thevcpupin
specified, thecpuset
specified bycpuset
here will be ignored. For virtual CPUs which don't havevcpupin
specified, each will be pinned to the physical CPUs specified bycpuset
here). Each element in that list is either a single CPU number, a range of CPU numbers, or a caret followed by a CPU number to be excluded from a previous range. Since 0.4.4current
The optional attribute
current
can be used to specify whether fewer than the maximum number of virtual CPUs should be enabled. Since 0.8.5placement
The optional attribute
placement
can be used to indicate the CPU placement mode for domain process. The value can be either "static" or "auto", but defaults toplacement
ofnumatune
or "static" ifcpuset
is specified. Using "auto" indicates the domain process will be pinned to the advisory nodeset from querying numad and the value of attributecpuset
will be ignored if it's specified. If bothcpuset
andplacement
are not specified or ifplacement
is "static", but nocpuset
is specified, the domain process will be pinned to all the available physical CPUs. Since 0.9.11 (QEMU and KVM only)
vcpus
The vcpus element allows to control state of individual vCPUs. The
id
attribute specifies the vCPU id as used by libvirt in other places such as vCPU pinning, scheduler information and NUMA assignment. Note that the vCPU ID as seen in the guest may differ from libvirt ID in certain cases. Valid IDs are from 0 to the maximum vCPU count as set by thevcpu
element minus 1. Theenabled
attribute allows to control the state of the vCPU. Valid values areyes
andno
.hotpluggable
controls whether given vCPU can be hotplugged and hotunplugged in cases when the CPU is enabled at boot. Note that all disabled vCPUs must be hotpluggable. Valid values areyes
andno
.order
allows to specify the order to add the online vCPUs. For hypervisors/platforms that require to insert multiple vCPUs at once the order may be duplicated across all vCPUs that need to be enabled at once. Specifying order is not necessary, vCPUs are then added in an arbitrary order. If order info is used, it must be used for all online vCPUs. Hypervisors may clear or update ordering information during certain operations to assure valid configuration. Note that hypervisors may create hotpluggable vCPUs differently from boot vCPUs thus special initialization may be necessary. Hypervisors may require that vCPUs enabled on boot which are not hotpluggable are clustered at the beginning starting with ID 0. It may be also required that vCPU 0 is always present and non-hotpluggable. Note that providing state for individual CPUs may be necessary to enable support of addressable vCPU hotplug and this feature may not be supported by all hypervisors. For QEMU the following conditions are required. vCPU 0 needs to be enabled and non-hotpluggable. On PPC64 along with it vCPUs that are in the same core need to be enabled as well. All non-hotpluggable CPUs present at boot need to be grouped after vCPU 0. Since 2.2.0 (QEMU only)
IOThreads Allocation
IOThreads are dedicated event loop threads for supported disk devices to perform block I/O requests in order to improve scalability especially on an SMP host/guest with many LUNs. Since 1.2.8 (QEMU only)
<domain>
...
<iothreads>4</iothreads>
...
</domain>
<domain>
...
<iothreadids>
<iothread id="2"/>
<iothread id="4"/>
<iothread id="6"/>
<iothread id="8"/>
</iothreadids>
...
</domain>
iothreads
The content of this optional element defines the number of IOThreads to be assigned to the domain for use by supported target storage devices. There should be only 1 or 2 IOThreads per host CPU. There may be more than one supported device assigned to each IOThread. Since 1.2.8
iothreadids
The optional
iothreadids
element provides the capability to specifically define the IOThread ID's for the domain. By default, IOThread ID's are sequentially numbered starting from 1 through the number ofiothreads
defined for the domain. Theid
attribute is used to define the IOThread ID. Theid
attribute must be a positive integer greater than 0. If there are lessiothreadids
defined thaniothreads
defined for the domain, then libvirt will sequentially filliothreadids
starting at 1 avoiding any predefinedid
. If there are moreiothreadids
defined thaniothreads
defined for the domain, then theiothreads
value will be adjusted accordingly. Since 1.2.15
CPU Tuning
<domain>
...
<cputune>
<vcpupin vcpu="0" cpuset="1-4,^2"/>
<vcpupin vcpu="1" cpuset="0,1"/>
<vcpupin vcpu="2" cpuset="2,3"/>
<vcpupin vcpu="3" cpuset="0,4"/>
<emulatorpin cpuset="1-3"/>
<iothreadpin iothread="1" cpuset="5,6"/>
<iothreadpin iothread="2" cpuset="7,8"/>
<shares>2048</shares>
<period>1000000</period>
<quota>-1</quota>
<global_period>1000000</global_period>
<global_quota>-1</global_quota>
<emulator_period>1000000</emulator_period>
<emulator_quota>-1</emulator_quota>
<iothread_period>1000000</iothread_period>
<iothread_quota>-1</iothread_quota>
<vcpusched vcpus='0-4,^3' scheduler='fifo' priority='1'/>
<iothreadsched iothreads='2' scheduler='batch'/>
<cachetune vcpus='0-3'>
<cache id='0' level='3' type='both' size='3' unit='MiB'/>
<cache id='1' level='3' type='both' size='3' unit='MiB'/>
<monitor level='3' vcpus='1'/>
<monitor level='3' vcpus='0-3'/>
</cachetune>
<cachetune vcpus='4-5'>
<monitor level='3' vcpus='4'/>
<monitor level='3' vcpus='5'/>
</cachetune>
<memorytune vcpus='0-3'>
<node id='0' bandwidth='60'/>
</memorytune>
</cputune>
...
</domain>
cputune
The optional
cputune
element provides details regarding the CPU tunable parameters for the domain. Note: for the qemu driver, the optionalvcpupin
andemulatorpin
pinning settings are honored after the emulator is launched and NUMA constraints considered. This means that it is expected that other physical CPUs of the host will be used during this time by the domain, which will be reflected by the output ofvirsh cpu-stats
. Since 0.9.0vcpupin
The optional
vcpupin
element specifies which of host's physical CPUs the domain vCPU will be pinned to. If this is omitted, and attributecpuset
of elementvcpu
is not specified, the vCPU is pinned to all the physical CPUs by default. It contains two required attributes, the attributevcpu
specifies vCPU id, and the attributecpuset
is same as attributecpuset
of elementvcpu
. QEMU driver support since 0.9.0, Xen driver support since 0.9.1emulatorpin
The optional
emulatorpin
element specifies which of host physical CPUs the "emulator", a subset of a domain not including vCPU or iothreads will be pinned to. If this is omitted, and attributecpuset
of elementvcpu
is not specified, "emulator" is pinned to all the physical CPUs by default. It contains one required attributecpuset
specifying which physical CPUs to pin to.iothreadpin
The optional
iothreadpin
element specifies which of host physical CPUs the IOThreads will be pinned to. If this is omitted and attributecpuset
of elementvcpu
is not specified, the IOThreads are pinned to all the physical CPUs by default. There are two required attributes, the attributeiothread
specifies the IOThread ID and the attributecpuset
specifying which physical CPUs to pin to. See the IOThreads Allocation section documenting valid values ofiothread
. Since 1.2.9shares
The optional
shares
element specifies the proportional weighted share for the domain. If this is omitted, it defaults to the OS provided defaults. NB, There is no unit for the value, it's a relative measure based on the setting of other VM, e.g. A VM configured with value 2048 will get twice as much CPU time as a VM configured with value 1024. The value should be in range [2, 262144]. Since 0.9.0period
The optional
period
element specifies the enforcement interval (unit: microseconds). Withinperiod
, each vCPU of the domain will not be allowed to consume more thanquota
worth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value. Only QEMU driver support since 0.9.4, LXC since 0.9.10quota
The optional
quota
element specifies the maximum allowed bandwidth (unit: microseconds). A domain withquota
as any negative value indicates that the domain has infinite bandwidth for vCPU threads, which means that it is not bandwidth controlled. The value should be in range [1000, 17592186044415] or less than 0. A quota with value 0 means no value. You can use this feature to ensure that all vCPUs run at the same speed. Only QEMU driver support since 0.9.4, LXC since 0.9.10global_period
The optional
global_period
element specifies the enforcement CFS scheduler interval (unit: microseconds) for the whole domain in contrast withperiod
which enforces the interval per vCPU. The value should be in range 1000, 1000000]. Aglobal_period
with value 0 means no value. Only QEMU driver support since 1.3.3global_quota
The optional
global_quota
element specifies the maximum allowed bandwidth (unit: microseconds) within a period for the whole domain. A domain withglobal_quota
as any negative value indicates that the domain has infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 17592186044415] or less than 0. Aglobal_quota
with value 0 means no value. Only QEMU driver support since 1.3.3emulator_period
The optional
emulator_period
element specifies the enforcement interval (unit: microseconds). Withinemulator_period
, emulator threads (those excluding vCPUs) of the domain will not be allowed to consume more thanemulator_quota
worth of runtime. The value should be in range [1000, 1000000]. A period with value 0 means no value. Only QEMU driver support since 0.10.0emulator_quota
The optional
emulator_quota
element specifies the maximum allowed bandwidth (unit: microseconds) for domain's emulator threads (those excluding vCPUs). A domain withemulator_quota
as any negative value indicates that the domain has infinite bandwidth for emulator threads (those excluding vCPUs), which means that it is not bandwidth controlled. The value should be in range [1000, 17592186044415] or less than 0. A quota with value 0 means no value. Only QEMU driver support since 0.10.0iothread_period
The optional
iothread_period
element specifies the enforcement interval (unit: microseconds) for IOThreads. Withiniothread_period
, each IOThread of the domain will not be allowed to consume more thaniothread_quota
worth of runtime. The value should be in range [1000, 1000000]. An iothread_period with value 0 means no value. Only QEMU driver support since 2.1.0iothread_quota
The optional
iothread_quota
element specifies the maximum allowed bandwidth (unit: microseconds) for IOThreads. A domain withiothread_quota
as any negative value indicates that the domain IOThreads have infinite bandwidth, which means that it is not bandwidth controlled. The value should be in range [1000, 17592186044415] or less than 0. Aniothread_quota
with value 0 means no value. You can use this feature to ensure that all IOThreads run at the same speed. Only QEMU driver support since 2.1.0vcpusched
,iothreadsched
andemulatorsched
The optional
vcpusched
,iothreadsched
andemulatorsched
elements specify the scheduler type (valuesbatch
,idle
,fifo
,rr
) for particular vCPU, IOThread and emulator threads respectively. Forvcpusched
andiothreadsched
the attributesvcpus
andiothreads
select which vCPUs/IOThreads this setting applies to, leaving them out sets the default. The elementemulatorsched
does not have that attribute. Validvcpus
values start at 0 through one less than the number of vCPU's defined for the domain. Validiothreads
values are described in the IOThreads Allocation section. If noiothreadids
are defined, then libvirt numbers IOThreads from 1 to the number ofiothreads
available for the domain. For real-time schedulers (fifo
,rr
), priority must be specified as well (and is ignored for non-real-time ones). The value range for the priority depends on the host kernel (usually 1-99). Since 1.2.13emulatorsched
since 5.3.0cachetune
Since 4.1.0Optional
cachetune
element can control allocations for CPU caches using the resctrl on the host. Whether or not is this supported can be gathered from capabilities where some limitations like minimum size and required granularity are reported as well. The required attributevcpus
specifies to which vCPUs this allocation applies. A vCPU can only be member of onecachetune
element allocation. The vCPUs specified by cachetune can be identical with those in memorytune, however they are not allowed to overlap. The optional, output onlyid
attribute identifies cache uniquely. Supported subelements are:cache
This optional element controls the allocation of CPU cache and has the following attributes:
level
Host cache level from which to allocate.
id
Host cache id from which to allocate.
type
Type of allocation. Can be
code
for code (instructions),data
for data orboth
for both code and data (unified). Currently the allocation can be done only with the same type as the host supports, meaning you cannot requestboth
for host with CDP (code/data prioritization) enabled.size
The size of the region to allocate. The value by default is in bytes, but the
unit
attribute can be used to scale the value.unit
(optional)If specified it is the unit such as KiB, MiB, GiB, or TiB (described in the
memory
element for Memory Allocation) in whichsize
is specified, defaults to bytes.
monitor
Since 4.10.0The optional element
monitor
creates the cache monitor(s) for current cache allocation and has the following required attributes:level
Host cache level the monitor belongs to.
vcpus
vCPU list the monitor applies to. A monitor's vCPU list can only be the member(s) of the vCPU list of the associated allocation. The default monitor has the same vCPU list as the associated allocation. For non-default monitors, overlapping vCPUs are not permitted.
memorytune
Since 4.7.0Optional
memorytune
element can control allocations for memory bandwidth using the resctrl on the host. Whether or not is this supported can be gathered from capabilities where some limitations like minimum bandwidth and required granularity are reported as well. The required attributevcpus
specifies to which vCPUs this allocation applies. A vCPU can only be member of onememorytune
element allocation. Thevcpus
specified bymemorytune
can be identical to those specified bycachetune
. However they are not allowed to overlap each other. Supported subelements are:node
This element controls the allocation of CPU memory bandwidth and has the following attributes:
id
Host node id from which to allocate memory bandwidth.
bandwidth
The memory bandwidth to allocate from this node. The value by default is in percentage.
Memory Allocation
<domain>
...
<maxMemory slots='16' unit='KiB'>1524288</maxMemory>
<memory unit='KiB'>524288</memory>
<currentMemory unit='KiB'>524288</currentMemory>
...
</domain>
memory
The maximum allocation of memory for the guest at boot time. The memory allocation includes possible additional memory devices specified at start or hotplugged later. The units for this value are determined by the optional attribute
unit
, which defaults to "KiB" (kibibytes, 210 or blocks of 1024 bytes). Valid units are "b" or "bytes" for bytes, "KB" for kilobytes (103 or 1,000 bytes), "k" or "KiB" for kibibytes (1024 bytes), "MB" for megabytes (106 or 1,000,000 bytes), "M" or "MiB" for mebibytes (220 or 1,048,576 bytes), "GB" for gigabytes (109 or 1,000,000,000 bytes), "G" or "GiB" for gibibytes (230 or 1,073,741,824 bytes), "TB" for terabytes (1012 or 1,000,000,000,000 bytes), or "T" or "TiB" for tebibytes (240 or 1,099,511,627,776 bytes). However, the value will be rounded up to the nearest kibibyte by libvirt, and may be further rounded to the granularity supported by the hypervisor. Some hypervisors also enforce a minimum, such as 4000KiB. In case NUMA is configured for the guest (See CPU model and topology) thememory
element can be omitted. In the case of crash, optional attributedumpCore
can be used to control whether the guest memory should be included in the generated coredump or not (values "on", "off").unit
since 0.9.11 ,dumpCore
since 0.10.2 (QEMU only)maxMemory
The run time maximum memory allocation of the guest. The initial memory specified by either the
<memory>
element or the NUMA cell size configuration can be increased by hot-plugging of memory to the limit specified by this element. Theunit
attribute behaves the same as for<memory>
. Theslots
attribute specifies the number of slots available for adding memory to the guest. The bounds are hypervisor specific. Note that due to alignment of the memory chunks added via memory hotplug the full size allocation specified by this element may be impossible to achieve. Since 1.2.14 supported by the QEMU driver.currentMemory
The actual allocation of memory for the guest. This value can be less than the maximum allocation, to allow for ballooning up the guests memory on the fly. If this is omitted, it defaults to the same value as the
memory
element. Theunit
attribute behaves the same as formemory
.
Memory Backing
<domain>
...
<memoryBacking>
<hugepages>
<page size="1" unit="G" nodeset="0-3,5"/>
<page size="2" unit="M" nodeset="4"/>
</hugepages>
<nosharepages/>
<locked/>
<source type="file|anonymous|memfd"/>
<access mode="shared|private"/>
<allocation mode="immediate|ondemand" threads='8'/>
<discard/>
</memoryBacking>
...
</domain>
The optional memoryBacking
element may contain several elements that influence how virtual memory pages are backed by host pages.
hugepages
This tells the hypervisor that the guest should have its memory allocated using hugepages instead of the normal native page size. Since 1.2.5 it's possible to set hugepages more specifically per numa node. The
page
element is introduced. It has one compulsory attributesize
which specifies which hugepages should be used (especially useful on systems supporting hugepages of different sizes). The default unit for thesize
attribute is kilobytes (multiplier of 1024). If you want to use different unit, use optionalunit
attribute. For systems with NUMA, the optionalnodeset
attribute may come handy as it ties given guest's NUMA nodes to certain hugepage sizes. From the example snippet, one gigabyte hugepages are used for every NUMA node except node number four. For the correct syntax see NUMA Node Tuning.nosharepages
Instructs hypervisor to disable shared pages (memory merge, KSM) for this domain. Since 1.0.6
locked
When set and supported by the hypervisor, memory pages belonging to the domain will be locked in host's memory and the host will not be allowed to swap them out, which might be required for some workloads such as real-time. For QEMU/KVM guests, the memory used by the QEMU process itself will be locked too: unlike guest memory, this is an amount libvirt has no way of figuring out in advance, so it has to remove the limit on locked memory altogether. Thus, enabling this option opens up to a potential security risk: the host will be unable to reclaim the locked memory back from the guest when it's running out of memory, which means a malicious guest allocating large amounts of locked memory could cause a denial-of-service attack on the host. Because of this, using this option is discouraged unless your workload demands it; even then, it's highly recommended to set a
hard_limit
(see Memory Tuning) on memory allocation suitable for the specific environment at the same time to mitigate the risks described above. Since 1.0.6source
Using the
type
attribute, it's possible to provide "file" to utilize file memorybacking or keep the default "anonymous". Since 4.10.0 , you may choose "memfd" backing. (QEMU/KVM only)access
Using the
mode
attribute, specify if the memory is to be "shared" or "private". This can be overridden per numa node bymemAccess
.allocation
Using the optional
mode
attribute, specify when to allocate the memory by supplying either "immediate" or "ondemand". Since 8.2.0 it is possible to set the number of threads that hypervisor uses to allocate memory viathreads
attribute.discard
When set and supported by hypervisor the memory content is discarded just before guest shuts down (or when DIMM module is unplugged). Please note that this is just an optimization and is not guaranteed to work in all cases (e.g. when hypervisor crashes). Since 4.4.0 (QEMU/KVM only)
Memory Tuning
<domain>
...
<memtune>
<hard_limit unit='G'>1</hard_limit>
<soft_limit unit='M'>128</soft_limit>
<swap_hard_limit unit='G'>2</swap_hard_limit>
<min_guarantee unit='bytes'>67108864</min_guarantee>
</memtune>
...
</domain>
memtune
The optional
memtune
element provides details regarding the memory tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults. For QEMU/KVM, the parameters are applied to the QEMU process as a whole. Thus, when counting them, one needs to add up guest RAM, guest video RAM, and some memory overhead of QEMU itself. The last piece is hard to determine so one needs guess and try. For each tunable, it is possible to designate which unit the number is in on input, using the same values as for<memory>
. For backwards compatibility, output is always in KiB.unit
since 0.9.11 Possible values for all *_limit parameters are in range from 0 to VIR_DOMAIN_MEMORY_PARAM_UNLIMITED.hard_limit
The optional
hard_limit
element is the maximum memory the guest can use. The units for this value are kibibytes (i.e. blocks of 1024 bytes). Users of QEMU and KVM are strongly advised not to set this limit as domain may get killed by the kernel if the guess is too low, and determining the memory needed for a process to run is an undecidable problem; that said, if you already setlocked
in Memory Backing because your workload demands it, you'll have to take into account the specifics of your deployment and figure out a value forhard_limit
that is large enough to support the memory requirements of your guest, but small enough to protect your host against a malicious guest locking all memory.soft_limit
The optional
soft_limit
element is the memory limit to enforce during memory contention. The units for this value are kibibytes (i.e. blocks of 1024 bytes)swap_hard_limit
The optional
swap_hard_limit
element is the maximum memory plus swap the guest can use. The units for this value are kibibytes (i.e. blocks of 1024 bytes). This has to be more than hard_limit value providedmin_guarantee
The optional
min_guarantee
element is the guaranteed minimum memory allocation for the guest. The units for this value are kibibytes (i.e. blocks of 1024 bytes). This element is only supported by VMware ESX and OpenVZ drivers.
NUMA Node Tuning
<domain>
...
<numatune>
<memory mode="strict" nodeset="1-4,^3"/>
<memnode cellid="0" mode="strict" nodeset="1"/>
<memnode cellid="2" mode="preferred" nodeset="2"/>
</numatune>
...
</domain>
numatune
The optional
numatune
element provides details of how to tune the performance of a NUMA host via controlling NUMA policy for domain process. NB, only supported by QEMU driver. Since 0.9.3memory
The optional
memory
element specifies how to allocate memory for the domain process on a NUMA host. It contains several optional attributes. Attributemode
is either 'interleave', 'strict', 'preferred', or 'restrictive', defaults to 'strict'. The value 'restrictive' specifies using system default policy and only cgroups is used to restrict the memory nodes, and it requires setting mode to 'restrictive' inmemnode
elements. Attributenodeset
specifies the NUMA nodes, using the same syntax as attributecpuset
of elementvcpu
. Attributeplacement
( since 0.9.12 ) can be used to indicate the memory placement mode for domain process, its value can be either "static" or "auto", defaults toplacement
ofvcpu
, or "static" ifnodeset
is specified. "auto" indicates the domain process will only allocate memory from the advisory nodeset returned from querying numad, and the value of attributenodeset
will be ignored if it's specified. Ifplacement
ofvcpu
is 'auto', andnumatune
is not specified, a defaultnumatune
withplacement
'auto' andmode
'strict' will be added implicitly. Since 0.9.3 See virDomainSetNumaParameters for more information on update of this element.memnode
Optional
memnode
elements can specify memory allocation policies per each guest NUMA node. For those nodes having no correspondingmemnode
element, the default from elementmemory
will be used. Attributecellid
addresses guest NUMA node for which the settings are applied. Attributesmode
andnodeset
have the same meaning and syntax as inmemory
element. This setting is not compatible with automatic placement. QEMU Since 1.2.7
Block I/O Tuning
<domain>
...
<blkiotune>
<weight>800</weight>
<device>
<path>/dev/sda</path>
<weight>1000</weight>
</device>
<device>
<path>/dev/sdb</path>
<weight>500</weight>
<read_bytes_sec>10000</read_bytes_sec>
<write_bytes_sec>10000</write_bytes_sec>
<read_iops_sec>20000</read_iops_sec>
<write_iops_sec>20000</write_iops_sec>
</device>
</blkiotune>
...
</domain>
blkiotune
The optional
blkiotune
element provides the ability to tune Blkio cgroup tunable parameters for the domain. If this is omitted, it defaults to the OS provided defaults. Since 0.8.8weight
The optional
weight
element is the overall I/O weight of the guest. The value should be in the range [100, 1000]. After kernel 2.6.39, the value could be in the range [10, 1000].device
The domain may have multiple
device
elements that further tune the weights for each host block device in use by the domain. Note that multiple disks (See Hard drives, floppy disks, CDROMs) can share a single host block device, if they are backed by files within the same host file system, which is why this tuning parameter is at the global domain level rather than associated with each guest disk device (contrast this to the <iotune> element of a disk definition (See Hard drives, floppy disks, CDROMs) which can applies to an individual disk). Eachdevice
element has two mandatory sub-elements,path
describing the absolute path of the device, andweight
giving the relative weight of that device, in the range [100, 1000]. After kernel 2.6.39, the value could be in the range [10, 1000]. Since 0.9.8 Additionally, the following optional sub-elements can be used:read_bytes_sec
Read throughput limit in bytes per second. Since 1.2.2
write_bytes_sec
Write throughput limit in bytes per second. Since 1.2.2
read_iops_sec
Read I/O operations per second limit. Since 1.2.2
write_iops_sec
Write I/O operations per second limit. Since 1.2.2
Resource partitioning
Hypervisors may allow for virtual machines to be placed into resource partitions, potentially with nesting of said partitions. The resource
element groups together configuration related to resource partitioning. It currently supports a child element partition
whose content defines the absolute path of the resource partition in which to place the domain. If no partition is listed, then the domain will be placed in a default partition. It is the responsibility of the app/admin to ensure that the partition exists prior to starting the guest. Only the (hypervisor specific) default partition can be assumed to exist by default.
...
<resource>
<partition>/virtualmachines/production</partition>
</resource>
...
Resource partitions are currently supported by the QEMU and LXC drivers, which map partition paths to cgroups directories, in all mounted controllers. Since 1.0.5
Fibre Channel VMID
The FC SAN can provide various QoS levels and access control depending on the VMID. It can also collect telemetry data at per-VM level which can be used to enhance the IO performance of the VM. This can be configured by using the appid
attribute of fibrechannel
element. The attribute contains single string (max 128 bytes) and it is used by kernel to create VMID.
...
<resource>
<fibrechannel appid='userProvidedID'/>
</resource>
...
Using this feature requires Fibre Channel capable HW, kernel compiled with option CONFIG_BLK_CGROUP_FC_APPID
and nvme_fc
kernel module loaded. Since 7.7.0
CPU model and topology
Requirements for CPU model, its features and topology can be specified using the following collection of elements. Since 0.7.5
...
<cpu match='exact'>
<model fallback='allow'>core2duo</model>
<vendor>Intel</vendor>
<topology sockets='1' dies='1' cores='2' threads='1'/>
<cache level='3' mode='emulate'/>
<feature policy='disable' name='lahf_lm'/>
</cpu>
...
<cpu mode='host-model'>
<model fallback='forbid'/>
<topology sockets='1' dies='1' cores='2' threads='1'/>
</cpu>
...
<cpu mode='host-passthrough' migratable='off'>
<cache mode='passthrough'/>
<feature policy='disable' name='lahf_lm'/>
...
<cpu mode='maximum' migratable='off'>
<cache mode='passthrough'/>
<feature policy='disable' name='lahf_lm'/>
...
In case no restrictions need to be put on CPU model and its features, a simpler cpu
element can be used. Since 0.7.6
...
<cpu>
<topology sockets='1' dies='1' cores='2' threads='1'/>
</cpu>
...
cpu
The
cpu
element is the main container for describing guest CPU requirements. Itsmatch
attribute specifies how strictly the virtual CPU provided to the guest matches these requirements. Since 0.7.6 thematch
attribute can be omitted iftopology
is the only element withincpu
. Possible values for thematch
attribute are:minimum
The specified CPU model and features describes the minimum requested CPU. A better CPU will be provided to the guest if it is possible with the requested hypervisor on the current host. This is a constrained
host-model
mode; the domain will not be created if the provided virtual CPU does not meet the requirements.exact
The virtual CPU provided to the guest should exactly match the specification. If such CPU is not supported, libvirt will refuse to start the domain.
strict
The domain will not be created unless the host CPU exactly matches the specification. This is not very useful in practice and should only be used if there is a real reason.
Since 0.8.5 the
match
attribute can be omitted and will default toexact
. Sometimes the hypervisor is not able to create a virtual CPU exactly matching the specification passed by libvirt. Since 3.2.0 , an optionalcheck
attribute can be used to request a specific way of checking whether the virtual CPU matches the specification. It is usually safe to omit this attribute when starting a domain and stick with the default value. Once the domain starts, libvirt will automatically change thecheck
attribute to the best supported value to ensure the virtual CPU does not change when the domain is migrated to another host. The following values can be used:none
Libvirt does no checking and it is up to the hypervisor to refuse to start the domain if it cannot provide the requested CPU. With QEMU this means no checking is done at all since the default behavior of QEMU is to emit warnings, but start the domain anyway.
partial
Libvirt will check the guest CPU specification before starting a domain, but the rest is left on the hypervisor. It can still provide a different virtual CPU.
full
The virtual CPU created by the hypervisor will be checked against the CPU specification and the domain will not be started unless the two CPUs match.
Since 0.9.10 , an optional
mode
attribute may be used to make it easier to configure a guest CPU to be as close to host CPU as possible. Possible values for themode
attribute are:custom
In this mode, the
cpu
element describes the CPU that should be presented to the guest. This is the default when nomode
attribute is specified. This mode makes it so that a persistent guest will see the same hardware no matter what host the guest is booted on.host-model
The
host-model
mode is essentially a shortcut to copying host CPU definition from capabilities XML into domain XML. Since the CPU definition is copied just before starting a domain, exactly the same XML can be used on different hosts while still providing the best guest CPU each host supports. Thematch
attribute can't be used in this mode. Specifying CPU model is not supported either, butmodel
'sfallback
attribute may still be used. Using thefeature
element, specific flags may be enabled or disabled specifically in addition to the host model. This may be used to fine tune features that can be emulated. (Since 1.1.1) . Libvirt does not model every aspect of each CPU so the guest CPU will not match the host CPU exactly. On the other hand, the ABI provided to the guest is reproducible. During migration, complete CPU model definition is transferred to the destination host so the migrated guest will see exactly the same CPU model for the running instance of the guest, even if the destination host contains more capable CPUs or newer kernel; but shutting down and restarting the guest may present different hardware to the guest according to the capabilities of the new host. Prior to libvirt 3.2.0 and QEMU 2.9.0 detection of the host CPU model via QEMU is not supported. Thus the CPU configuration created usinghost-model
may not work as expected. Since 3.2.0 and QEMU 2.9.0 this mode works the way it was designed and it is indicated by thefallback
attribute set toforbid
in the host-model CPU definition advertised in domain capabilities XML. Whenfallback
attribute is set toallow
in the domain capabilities XML, it is recommended to usecustom
mode with just the CPU model from the host capabilities XML. Since 1.2.11 PowerISA allows processors to run VMs in binary compatibility mode supporting an older version of ISA. Libvirt on PowerPC architecture uses thehost-model
to signify a guest mode CPU running in binary compatibility mode. Example: When a user needs a power7 VM to run in compatibility mode on a Power8 host, this can be described in XML as follows :<cpu mode='host-model'> <model>power7</model> </cpu> ...
host-passthrough
With this mode, the CPU visible to the guest should be exactly the same as the host CPU even in the aspects that libvirt does not understand. Though the downside of this mode is that the guest environment cannot be reproduced on different hardware. Thus, if you hit any bugs, you are on your own. Further details of that CPU can be changed using
feature
elements. Migration of a guest using host-passthrough is dangerous if the source and destination hosts are not identical in both hardware, QEMU version, microcode version and configuration. If such a migration is attempted then the guest may hang or crash upon resuming execution on the destination host. Depending on hypervisor version the virtual CPU may or may not contain features which may block migration even to an identical host. Since 6.5.0 optionalmigratable
attribute may be used to explicitly request such features to be removed from (on
) or kept in (off
) the virtual CPU. This attribute does not make migration to another host safer: even withmigratable='on'
migration will be dangerous unless both hosts are identical as described above.maximum
When running a guest with hardware virtualization this CPU model is functionally identical to
host-passthrough
, so refer to the docs above.When running a guest with CPU emulation, this CPU model will enable the maximum set of features that the emulation engine is able to support. Note that even with
migratable='on'
migration will be dangerous unless both hosts are running identical versions of the emulation code.Since 7.1.0 with the QEMU driver.
Both
host-model
andhost-passthrough
modes make sense when a domain can run directly on the host CPUs (for example, domains with typekvm
orhvf
). The actual host CPU is irrelevant for domains with emulated virtual CPUs (such as domains with typeqemu
). However, for backward compatibilityhost-model
may be implemented even for domains running on emulated CPUs in which case the best CPU the hypervisor is able to emulate may be used rather then trying to mimic the host CPU model.If an application does not care about a specific CPU, just wants the best featureset without a need for migration compatibility, the
maximum
model is a good choice on hypervisors where it is available.model
The content of the
model
element specifies CPU model requested by the guest. The list of available CPU models and their definition can be found in directorycpu_map
, installed in libvirt's data directory. If a hypervisor is not able to use the exact CPU model, libvirt automatically falls back to a closest model supported by the hypervisor while maintaining the list of CPU features. Since 0.9.10 , an optionalfallback
attribute can be used to forbid this behavior, in which case an attempt to start a domain requesting an unsupported CPU model will fail. Supported values forfallback
attribute are:allow
(this is the default), andforbid
. The optionalvendor_id
attribute ( Since 0.10.0 ) can be used to set the vendor id seen by the guest. It must be exactly 12 characters long. If not set the vendor id of the host is used. Typical possible values are "AuthenticAMD" and "GenuineIntel".vendor
Since 0.8.3 the content of the
vendor
element specifies CPU vendor requested by the guest. If this element is missing, the guest can be run on a CPU matching given features regardless on its vendor. The list of supported vendors can be found incpu_map/*_vendors.xml
.topology
The
topology
element specifies requested topology of virtual CPU provided to the guest. Four attributes,sockets
,dies
,cores
, andthreads
, accept non-zero positive integer values. They refer to the total number of CPU sockets, number of dies per socket, number of cores per die, and number of threads per core, respectively. Thedies
attribute is optional and will default to 1 if omitted, while the other attributes are all mandatory. Hypervisors may require that the maximum number of vCPUs specified by thecpus
element equals to the number of vcpus resulting from the topology.feature
The
cpu
element can contain zero or morefeature
elements used to fine-tune features provided by the selected CPU model. The list of known feature names can be found in the same file as CPU models. The meaning of eachfeature
element depends on itspolicy
attribute, which has to be set to one of the following values:force
The virtual CPU will claim the feature is supported regardless of it being supported by host CPU.
require
Guest creation will fail unless the feature is supported by the host CPU or the hypervisor is able to emulate it.
optional
The feature will be supported by virtual CPU if and only if it is supported by host CPU.
disable
The feature will not be supported by virtual CPU.
forbid
Guest creation will fail if the feature is supported by host CPU.
Since 0.8.5 the
policy
attribute can be omitted and will default torequire
.Individual CPU feature names are specified as part of the
name
attribute. For example, to explicitly specify the 'pcid' feature with Intel IvyBridge CPU model:... <cpu match='exact'> <model fallback='forbid'>IvyBridge</model> <vendor>Intel</vendor> <feature policy='require' name='pcid'/> </cpu> ...
cache
Since 3.3.0 the
cache
element describes the virtual CPU cache. If the element is missing, the hypervisor will use a sensible default.level
This optional attribute specifies which cache level is described by the element. Missing attribute means the element describes all CPU cache levels at once. Mixing
cache
elements with thelevel
attribute set and those without the attribute is forbidden.mode
The following values are supported:
emulate
The hypervisor will provide a fake CPU cache data.
passthrough
The real CPU cache data reported by the host CPU will be passed through to the virtual CPU.
disable
The virtual CPU will report no CPU cache of the specified level (or no cache at all if the
level
attribute is missing).
Guest NUMA topology can be specified using the numa
element. Since 0.9.8
...
<cpu>
...
<numa>
<cell id='0' cpus='0-3' memory='512000' unit='KiB' discard='yes'/>
<cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/>
</numa>
...
</cpu>
...
Each cell
element specifies a NUMA cell or a NUMA node. cpus
specifies the CPU or range of CPUs that are part of the node. Since 6.5.0 For the qemu driver, if the emulator binary supports disjointed cpus
ranges in each cell
, the sum of all CPUs declared in each cell
will be matched with the maximum number of virtual CPUs declared in the vcpu
element. This is done by filling any remaining CPUs into the first NUMA cell
. Users are encouraged to supply a complete NUMA topology, where the sum of the NUMA CPUs matches the maximum virtual CPUs number declared in vcpus
, to make the domain consistent across qemu and libvirt versions. memory
specifies the node memory in kibibytes (i.e. blocks of 1024 bytes). Since 6.6.0 the cpus
attribute is optional and if omitted a CPU-less NUMA node is created. Since 1.2.11 one can use an additional unit
attribute (See Memory Allocation) to define units in which memory
is specified. Since 1.2.7 all cells should have id
attribute in case referring to some cell is necessary in the code, otherwise the cells are assigned id
s in the increasing order starting from 0. Mixing cells with and without the id
attribute is not recommended as it may result in unwanted behaviour. Since 1.2.9 the optional attribute memAccess
can control whether the memory is to be mapped as "shared" or "private". This is valid only for hugepages-backed memory and nvdimm modules. Each cell
element can have an optional discard
attribute which fine tunes the discard feature for given numa node as described under Memory Backing. Accepted values are yes
and no
. Since 4.4.0
This guest NUMA specification is currently available only for QEMU/KVM and Xen.
A NUMA hardware architecture supports the notion of distances between NUMA cells. Since 3.10.0 it is possible to define the distance between NUMA cells using the distances
element within a NUMA cell
description. The sibling
sub-element is used to specify the distance value between sibling NUMA cells. For more details, see the chapter explaining the system's SLIT (System Locality Information Table) within the ACPI (Advanced Configuration and Power Interface) specification.
...
<cpu>
...
<numa>
<cell id='0' cpus='0,4-7' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='10'/>
<sibling id='1' value='21'/>
<sibling id='2' value='31'/>
<sibling id='3' value='41'/>
</distances>
</cell>
<cell id='1' cpus='1,8-10,12-15' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='21'/>
<sibling id='1' value='10'/>
<sibling id='2' value='21'/>
<sibling id='3' value='31'/>
</distances>
</cell>
<cell id='2' cpus='2,11' memory='512000' unit='KiB' memAccess='shared'>
<distances>
<sibling id='0' value='31'/>
<sibling id='1' value='21'/>
<sibling id='2' value='10'/>
<sibling id='3' value='21'/>
</distances>
</cell>
<cell id='3' cpus='3' memory='512000' unit='KiB'>
<distances>
<sibling id='0' value='41'/>
<sibling id='1' value='31'/>
<sibling id='2' value='21'/>
<sibling id='3' value='10'/>
</distances>
</cell>
</numa>
...
</cpu>
...
Describing distances between NUMA cells is currently only supported by Xen and QEMU. If no distances
are given to describe the SLIT data between different cells, it will default to a scheme using 10 for local and 20 for remote distances.
ACPI Heterogeneous Memory Attribute Table
...
<cpu>
...
<numa>
<cell id='0' cpus='0-3' memory='2097152' unit='KiB' discard='yes'>
<cache level='1' associativity='direct' policy='writeback'>
<size value='10' unit='KiB'/>
<line value='8' unit='B'/>
</cache>
</cell>
<cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/>
<interconnects>
<latency initiator='0' target='0' type='access' value='5'/>
<latency initiator='0' target='0' cache='1' type='access' value='10'/>
<bandwidth initiator='0' target='0' type='access' value='204800' unit='KiB'/>
</interconnects>
</numa>
...
</cpu>
...
Since 6.6.0 the cell
element can have a cache
child element which describes memory side cache for memory proximity domains. The cache
element has a level
attribute describing the cache level and thus the element can be repeated multiple times to describe different levels of the cache.
The cache
element then has following mandatory attributes:
level
Level of the cache this description refers to.
associativity
Describes cache associativity (accepted values are
none
,direct
andfull
).policy
Describes cache write associativity (accepted values are
none
,writeback
andwritethrough
).
The cache
element has two mandatory child elements then: size
and line
which describe cache size and cache line size. Both elements accept two attributes: value
and unit
which set the value of corresponding cache attribute.
The NUMA description has an optional interconnects
element that describes the normalized memory read/write latency, read/write bandwidth between Initiator Proximity Domains (Processor or I/O) and Target Proximity Domains (Memory).
The interconnects
element can have zero or more latency
child elements to describe latency between two memory nodes and zero or more bandwidth
child elements to describe bandwidth between two memory nodes. Both these have the following mandatory attributes:
initiator
Refers to the source NUMA node
target
Refers to the target NUMA node
type
The type of the access. Accepted values:
access
,read
,write
value
The actual value. For latency this is delay in nanoseconds, for bandwidth this value is in kibibytes per second. Use additional
unit
attribute to change the units.
To describe latency from one NUMA node to a cache of another NUMA node the latency
element has optional cache
attribute which in combination with target
attribute creates full reference to distant NUMA node's cache level. For instance, target='0' cache='1'
refers to the first level cache of NUMA node 0.
Events configuration
It is sometimes necessary to override the default actions taken on various events. Not all hypervisors support all events and actions. The actions may be taken as a result of calls to libvirt APIs virDomainReboot , virDomainShutdown , or virDomainShutdownFlags . Using virsh reboot
or virsh shutdown
would also trigger the event.
...
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>restart</on_crash>
<on_lockfailure>poweroff</on_lockfailure>
...
The following collections of elements allow the actions to be specified when a guest OS triggers a lifecycle operation. A common use case is to force a reboot to be treated as a poweroff when doing the initial OS installation. This allows the VM to be re-configured for the first post-install bootup.
on_poweroff
The content of this element specifies the action to take when the guest requests a poweroff.
on_reboot
The content of this element specifies the action to take when the guest requests a reboot.
on_crash
The content of this element specifies the action to take when the guest crashes.
Each of these states allow for the same four possible actions.
destroy
The domain will be terminated completely and all resources released.
restart
The domain will be terminated and then restarted with the same configuration.
preserve
The domain will be terminated and its resource preserved to allow analysis.
rename-restart
The domain will be terminated and then restarted with a new name. (Only supported by the libxl hypervisor driver.)
QEMU/KVM/HVF supports the on_poweroff
and on_reboot
events handling the destroy
and restart
actions, but the combination of on_poweroff
set to restart
and on_reboot
set to destroy
is forbidden.
The on_crash
event supports these additional actions since 0.8.4 .
coredump-destroy
The crashed domain's core will be dumped, and then the domain will be terminated completely and all resources released
coredump-restart
The crashed domain's core will be dumped, and then the domain will be restarted with the same configuration
Since 3.9.0 , the lifecycle events can be configured via the virDomainSetLifecycleAction API.
The on_lockfailure
element ( since 1.0.0 ) may be used to configure what action should be taken when a lock manager loses resource locks. The following actions are recognized by libvirt, although not all of them need to be supported by individual lock managers. When no action is specified, each lock manager will take its default action.
poweroff
The domain will be forcefully powered off.
restart
The domain will be powered off and started up again to reacquire its locks.
pause
The domain will be paused so that it can be manually resumed when lock issues are solved.
ignore
Keep the domain running as if nothing happened.
Power Management
Since 0.10.2 it is possible to forcibly enable or disable BIOS advertisements to the guest OS. (NB: Only qemu driver support)
...
<pm>
<suspend-to-disk enabled='no'/>
<suspend-to-mem enabled='yes'/>
</pm>
...
pm
These elements enable ('yes') or disable ('no') BIOS support for S3 (suspend-to-mem) and S4 (suspend-to-disk) ACPI sleep states. If nothing is specified, then the hypervisor will be left with its default value. Note: This setting cannot prevent the guest OS from performing a suspend as the guest OS itself can choose to circumvent the unavailability of the sleep states (e.g. S4 by turning off completely).
Hypervisor features
Hypervisors may allow certain CPU / machine features to be toggled on/off.
...
<features>
<pae/>
<acpi/>
<apic/>
<hap/>
<privnet/>
<hyperv mode='custom'>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='4096'/>
<vpindex state='on'/>
<runtime state='on'/>
<synic state='on'/>
<stimer state='on'>
<direct state='on'/>
</stimer>
<reset state='on'/>
<vendor_id state='on' value='KVM Hv'/>
<frequencies state='on'/>
<reenlightenment state='on'/>
<tlbflush state='on'/>
<ipi state='on'/>
<evmcs state='on'/>
</hyperv>
<kvm>
<hidden state='on'/>
<hint-dedicated state='on'/>
<poll-control state='on'/>
<pv-ipi state='off'/>
<dirty-ring state='on' size='4096'/>
</kvm>
<xen>
<e820_host state='on'/>
<passthrough state='on' mode='share_pt'/>
</xen>
<pvspinlock state='on'/>
<gic version='2'/>
<ioapic driver='qemu'/>
<hpt resizing='required'>
<maxpagesize unit='MiB'>16</maxpagesize>
</hpt>
<vmcoreinfo state='on'/>
<smm state='on'>
<tseg unit='MiB'>48</tseg>
</smm>
<htm state='on'/>
<ccf-assist state='on'/>
<msrs unknown='ignore'/>
<cfpc value='workaround'/>
<sbbc value='workaround'/>
<ibs value='fixed-na'/>
<tcg>
<tb-cache unit='MiB'>128</tb-cache>
</tcg>
</features>
...
All features are listed within the features
element, omitting a togglable feature tag turns it off. The available features can be found by asking for the capabilities XML and domain capabilities XML, but a common set for fully virtualized domains are:
pae
Physical address extension mode allows 32-bit guests to address more than 4 GB of memory.
acpi
ACPI is useful for power management, for example, with KVM or HVF guests it is required for graceful shutdown to work.
apic
APIC allows the use of programmable IRQ management. Since 0.10.2 (QEMU only) there is an optional attribute
eoi
with valueson
andoff
which toggles the availability of EOI (End of Interrupt) for the guest.hap
Depending on the
state
attribute (valueson
,off
) enable or disable use of Hardware Assisted Paging. The default ison
if the hypervisor detects availability of Hardware Assisted Paging.viridian
Enable Viridian hypervisor extensions for paravirtualizing guest operating systems
privnet
Always create a private network namespace. This is automatically set if any interface devices are defined. This feature is only relevant for container based virtualization drivers, such as LXC.
hyperv
Enable various features improving behavior of guests running Microsoft Windows.
Feature Description Value Since relaxed Relax constraints on timers on, off 1.0.0 (QEMU 2.0) vapic Enable virtual APIC on, off 1.1.0 (QEMU 2.0) spinlocks Enable spinlock support on, off; retries - at least 4095 1.1.0 (QEMU 2.0) vpindex Virtual processor index on, off 1.3.3 (QEMU 2.5) runtime Processor time spent on running guest code and on behalf of guest code on, off 1.3.3 (QEMU 2.5) synic Enable Synthetic Interrupt Controller (SynIC) on, off 1.3.3 (QEMU 2.6) stimer Enable SynIC timers, optionally with Direct Mode support on, off; direct - on,off 1.3.3 (QEMU 2.6), direct mode 5.7.0 (QEMU 4.1) reset Enable hypervisor reset on, off 1.3.3 (QEMU 2.5) vendor_id Set hypervisor vendor id on, off; value - string, up to 12 characters 1.3.3 (QEMU 2.5) frequencies Expose frequency MSRs on, off 4.7.0 (QEMU 2.12) reenlightenment Enable re-enlightenment notification on migration on, off 4.7.0 (QEMU 3.0) tlbflush Enable PV TLB flush support on, off 4.7.0 (QEMU 3.0) ipi Enable PV IPI support on, off 4.10.0 (QEMU 3.1) evmcs Enable Enlightened VMCS on, off 4.10.0 (QEMU 3.1) Since 8.0.0 , the hypervisor can be configured further by setting the
mode
attribute to one of the following values:custom
Set exactly the specified features.
passthrough
Enable all features currently supported by the hypervisor, even those that libvirt does not understand. Migration of a guest using passthrough is dangerous if the source and destination hosts are not identical in both hardware, QEMU version, microcode version and configuration. If such a migration is attempted then the guest may hang or crash upon resuming execution on the destination host. Depending on hypervisor version the virtual CPU may or may not contain features which may block migration even to an identical host.
The
mode
attribute can be omitted and will default tocustom
.pvspinlock
Notify the guest that the host supports paravirtual spinlocks for example by exposing the pvticketlocks mechanism. This feature can be explicitly disabled by using
state='off'
attribute.kvm
Various features to change the behavior of the KVM hypervisor.
Feature Description Value Since hidden Hide the KVM hypervisor from standard MSR based discovery on, off 1.2.8 (QEMU 2.1.0) hint-dedicated Allows a guest to enable optimizations when running on dedicated vCPUs on, off 5.7.0 (QEMU 2.12.0) poll-control Decrease IO completion latency by introducing a grace period of busy waiting on, off 6.10.0 (QEMU 4.2) pv-ipi Paravirtualized send IPIs on, off 7.10.0 (QEMU 3.1) dirty-ring Enable dirty ring feature on, off; size - must be power of 2, range [1024,65536] 8.0.0 (QEMU 6.1) xen
Various features to change the behavior of the Xen hypervisor.
Feature Description Value Since e820_host Expose the host e820 to the guest (PV only) on, off 6.3.0 passthrough Enable IOMMU mappings allowing PCI passthrough on, off; mode - optional string sync_pt or share_pt 6.3.0 pmu
Depending on the
state
attribute (valueson
,off
, defaulton
) enable or disable the performance monitoring unit for the guest. Since 1.2.12vmport
Depending on the
state
attribute (valueson
,off
, defaulton
) enable or disable the emulation of VMware IO port, for vmmouse etc. Since 1.2.16gic
Enable for architectures using a General Interrupt Controller instead of APIC in order to handle interrupts. For example, the 'aarch64' architecture uses
gic
instead ofapic
. The optional attributeversion
specifies the GIC version; however, it may not be supported by all hypervisors. Accepted values are2
,3
andhost
. Since 1.2.16smm
Depending on the
state
attribute (valueson
,off
, defaulton
) enable or disable System Management Mode. Since 2.1.0Optional sub-element
tseg
can be used to specify the amount of memory dedicated to SMM's extended TSEG. That offers a fourth option size apart from the existing ones (1 MiB, 2 MiB and 8 MiB) that the guest OS (or rather loader) can choose from. The size can be specified as a value of that element, optional attributeunit
can be used to specify the unit of the aforementioned value (defaults to 'MiB'). If set to 0 the extended size is not advertised and only the default ones (see above) are available.If the VM is booting you should leave this option alone, unless you are very certain you know what you are doing.
This value is configurable due to the fact that the calculation cannot be done right with the guarantee that it will work correctly. In QEMU, the user-configurable extended TSEG feature was unavailable up to and including
pc-q35-2.9
. Starting withpc-q35-2.10
the feature is available, with default size 16 MiB. That should suffice for up to roughly 272 vCPUs, 5 GiB guest RAM in total, no hotplug memory range, and 32 GiB of 64-bit PCI MMIO aperture. Or for 48 vCPUs, with 1TB of guest RAM, no hotplug DIMM range, and 32GB of 64-bit PCI MMIO aperture. The values may also vary based on the loader the VM is using.Additional size might be needed for significantly higher vCPU counts or increased address space (that can be memory, maxMemory, 64-bit PCI MMIO aperture size; roughly 8 MiB of TSEG per 1 TiB of address space) which can also be rounded up.
Due to the nature of this setting being similar to "how much RAM should the guest have" users are advised to either consult the documentation of the guest OS or loader (if there is any), or test this by trial-and-error changing the value until the VM boots successfully. Yet another guiding value for users might be the fact that 48 MiB should be enough for pretty large guests (240 vCPUs and 4TB guest RAM), but it is on purpose not set as default as 48 MiB of unavailable RAM might be too much for small guests (e.g. with 512 MiB of RAM).
See Memory Allocation for more details about the
unit
attribute. Since 4.5.0 (QEMU only)ioapic
Tune the I/O APIC. Possible values for the
driver
attribute are:kvm
(default for KVM domains) andqemu
which puts I/O APIC in userspace which is also known as a split I/O APIC mode. Since 3.4.0 (QEMU/KVM only)hpt
Configure the HPT (Hash Page Table) of a pSeries guest. Possible values for the
resizing
attribute areenabled
, which causes HPT resizing to be enabled if both the guest and the host support it;disabled
, which causes HPT resizing to be disabled regardless of guest and host support; andrequired
, which prevents the guest from starting unless both the guest and the host support HPT resizing. If the attribute is not defined, the hypervisor default will be used. Since 3.10.0 (QEMU/KVM only).The optional
maxpagesize
subelement can be used to limit the usable page size for HPT guests. Common values are 64 KiB, 16 MiB and 16 GiB; when not specified, the hypervisor default will be used. Since 4.5.0 (QEMU/KVM only).vmcoreinfo
Enable QEMU vmcoreinfo device to let the guest kernel save debug details. Since 4.4.0 (QEMU only)
htm
Configure HTM (Hardware Transational Memory) availability for pSeries guests. Possible values for the
state
attribute areon
andoff
. If the attribute is not defined, the hypervisor default will be used. Since 4.6.0 (QEMU/KVM only)nested-hv
Configure nested HV availability for pSeries guests. This needs to be enabled from the host (L0) in order to be effective; having HV support in the (L1) guest is very desiderable if it's planned to run nested (L2) guests inside it, because it will result in those nested guests having much better performance than they would when using KVM PR or TCG. Possible values for the
state
attribute areon
andoff
. If the attribute is not defined, the hypervisor default will be used. Since 4.10.0 (QEMU/KVM only)msrs
Some guests might require ignoring unknown Model Specific Registers (MSRs) reads and writes. It's possible to switch this by setting
unknown
attribute ofmsrs
toignore
. If the attribute is not defined, or set tofault
, unknown reads and writes will not be ignored. Since 5.1.0 (bhyve only)ccf-assist
Configure ccf-assist (Count Cache Flush Assist) availability for pSeries guests. Possible values for the
state
attribute areon
andoff
. If the attribute is not defined, the hypervisor default will be used. Since 5.9.0 (QEMU/KVM only)cfpc
Configure cfpc (Cache Flush on Privilege Change) availability for pSeries guests. Possible values for the
value
attribute arebroken
(no protection),workaround
(software workaround available) andfixed
(fixed in hardware). If the attribute is not defined, the hypervisor default will be used. Since 6.3.0 (QEMU/KVM only)sbbc
Configure sbbc (Speculation Barrier Bounds Checking) availability for pSeries guests. Possible values for the
value
attribute arebroken
(no protection),workaround
(software workaround available) andfixed
(fixed in hardware). If the attribute is not defined, the hypervisor default will be used. Since 6.3.0 (QEMU/KVM only)ibs
Configure ibs (Indirect Branch Speculation) availability for pSeries guests. Possible values for the
value
attribute arebroken
(no protection),workaround
(count cache flush),fixed-ibs
(fixed by serializing indirect branches),fixed-ccd
(fixed by disabling the cache count) andfixed-na (fixed in hardware - no longer applicable)
. If the attribute is not defined, the hypervisor default will be used. Since 6.3.0 (QEMU/KVM only)tcg
Various features to change the behavior of the TCG accelerator.
Feature Description Value Since tb-cache The size of translation block cache size an integer (a multiple of MiB) 8.0.0
Time keeping
The guest clock is typically initialized from the host clock. Most operating systems expect the hardware clock to be kept in UTC, and this is the default. Windows, however, expects it to be in so called 'localtime'.
...
<clock offset='localtime'>
<timer name='rtc' tickpolicy='catchup' track='guest'>
<catchup threshold='123' slew='120' limit='10000'/>
</timer>
<timer name='pit' tickpolicy='delay'/>
</clock>
...
clock
The
offset
attribute takes four possible values, allowing fine grained control over how the guest clock is synchronized to the host. NB, not all hypervisors support all modes.utc
The guest clock will always be synchronized to UTC when booted. Since 0.9.11 'utc' mode can be converted to 'variable' mode, which can be controlled by using the
adjustment
attribute. If the value is 'reset', the conversion is never done (not all hypervisors can synchronize to UTC on each boot; use of 'reset' will cause an error on those hypervisors). A numeric value forces the conversion to 'variable' mode using the value as the initial adjustment. The defaultadjustment
is hypervisor specific.localtime
The guest clock will be synchronized to the host's configured timezone when booted, if any. Since 0.9.11, the
adjustment
attribute behaves the same as in 'utc' mode.timezone
The guest clock will be synchronized to the requested timezone using the
timezone
attribute. Since 0.7.7variable
The guest clock will have an arbitrary offset applied relative to UTC or localtime, depending on the
basis
attribute. The delta relative to UTC (or localtime) is specified in seconds, using theadjustment
attribute. The guest is free to adjust the RTC over time and expect that it will be honored at next reboot. This is in contrast to 'utc' and 'localtime' mode (with the optional attribute adjustment='reset'), where the RTC adjustments are lost at each reboot. Since 0.7.7 Since 0.9.11 thebasis
attribute can be either 'utc' (default) or 'localtime'.absolute
The guest clock will be always set to the value of the
start
attribute at startup of the domain. Thestart
attribute takes an epoch timestamp. Since 8.4.0.
A
clock
may have zero or moretimer
sub-elements. Since 0.8.0timer
Each timer element requires a
name
attribute, and has other optional attributes that depend on thename
specified. Various hypervisors support different combinations of attributes.name
The
name
attribute selects which timer is being modified, and can be one of "platform" (currently unsupported), "hpet" (xen, qemu, lxc), "kvmclock" (qemu), "pit" (qemu), "rtc" (qemu, lxc), "tsc" (xen, qemu -since 3.2.0 ), "hypervclock" (qemu - since 1.2.2 ) or "armvtimer" (qemu - since 6.1.0 ). Thehypervclock
timer adds support for the reference time counter and the reference page for iTSC feature for guests running the Microsoft Windows operating system.track
The
track
attribute specifies what the timer tracks, and can be "boot", "guest", or "wall", or "realtime". Only valid forname="rtc"
orname="platform"
.tickpolicy
The
tickpolicy
attribute determines what happens when QEMU misses a deadline for injecting a tick to the guest. This can happen, for example, because the guest was paused.delay
Continue to deliver ticks at the normal rate. The guest OS will not notice anything is amiss, as from its point of view time will have continued to flow normally. The time in the guest should now be behind the time in the host by exactly the amount of time during which ticks have been missed.
catchup
Deliver ticks at a higher rate to catch up with the missed ticks. The guest OS will not notice anything is amiss, as from its point of view time will have continued to flow normally. Once the timer has managed to catch up with all the missing ticks, the time in the guest and in the host should match.
merge
Merge the missed tick(s) into one tick and inject. The guest time may be delayed, depending on how the OS reacts to the merging of ticks
discard
Throw away the missed ticks and continue with future injection normally. The guest OS will see the timer jump ahead by a potentially quite significant amount all at once, as if the intervening chunk of time had simply not existed; needless to say, such a sudden jump can easily confuse a guest OS which is not specifically prepared to deal with it. Assuming the guest OS can deal correctly with the time jump, the time in the guest and in the host should now match.
If the policy is "catchup", there can be further details in the
catchup
sub-element.catchup
The
catchup
element has three optional attributes, each a positive integer. The attributes arethreshold
,slew
, andlimit
.
Note that hypervisors are not required to support all policies across all time sources
frequency
The
frequency
attribute is an unsigned integer specifying the frequency at whichname="tsc"
runs.mode
The
mode
attribute controls how thename="tsc"
timer is managed, and can be "auto", "native", "emulate", "paravirt", or "smpsafe". Other timers are always emulated.present
The
present
attribute can be "yes" or "no" to specify whether a particular timer is available to the guest.
Performance monitoring events
Some platforms allow monitoring of performance of the virtual machine and the code executed inside. To enable the performance monitoring events you can either specify them in the perf
element or enable them via virDomainSetPerfEvents
API. The performance values are then retrieved using the virConnectGetAllDomainStats API. Since 2.0.0
...
<perf>
<event name='cmt' enabled='yes'/>
<event name='mbmt' enabled='no'/>
<event name='mbml' enabled='yes'/>
<event name='cpu_cycles' enabled='no'/>
<event name='instructions' enabled='yes'/>
<event name='cache_references' enabled='no'/>
<event name='cache_misses' enabled='no'/>
<event name='branch_instructions' enabled='no'/>
<event name='branch_misses' enabled='no'/>
<event name='bus_cycles' enabled='no'/>
<event name='stalled_cycles_frontend' enabled='no'/>
<event name='stalled_cycles_backend' enabled='no'/>
<event name='ref_cpu_cycles' enabled='no'/>
<event name='cpu_clock' enabled='no'/>
<event name='task_clock' enabled='no'/>
<event name='page_faults' enabled='no'/>
<event name='context_switches' enabled='no'/>
<event name='cpu_migrations' enabled='no'/>
<event name='page_faults_min' enabled='no'/>
<event name='page_faults_maj' enabled='no'/>
<event name='alignment_faults' enabled='no'/>
<event name='emulation_faults' enabled='no'/>
</perf>
...
event name | Description | stats parameter name |
---|---|---|
cmt |
usage of l3 cache in bytes by applications running on the platform | perf.cmt |
mbmt |
total system bandwidth from one level of cache | perf.mbmt |
mbml |
bandwidth of memory traffic for a memory controller | perf.mbml |
cpu_cycles |
the count of CPU cycles (total/elapsed) | perf.cpu_cycles |
instructions |
the count of instructions by applications running on the platform | perf.instructions |
cache_references |
the count of cache hits by applications running on the platform | perf.cache_references |
cache_misses |
the count of cache misses by applications running on the platform | perf.cache_misses |
branch_instructions |
the count of branch instructions by applications running on the platform | perf.branch_instructions |
branch_misses |
the count of branch misses by applications running on the platform | perf.branch_misses |
bus_cycles |
the count of bus cycles by applications running on the platform | perf.bus_cycles |
stalled_cycles_frontend |
the count of stalled CPU cycles in the frontend of the instruction processor pipeline by applications running on the platform | perf.stalled_cycles_frontend |
stalled_cycles_backend |
the count of stalled CPU cycles in the backend of the instruction processor pipeline by applications running on the platform | perf.stalled_cycles_backend |
ref_cpu_cycles |
the count of total CPU cycles not affected by CPU frequency scaling by applications running on the platform | perf.ref_cpu_cycles |
cpu_clock |
the count of CPU clock time, as measured by a monotonic high-resolution per-CPU timer, by applications running on the platform | perf.cpu_clock |
task_clock |
the count of task clock time, as measured by a monotonic high-resolution CPU timer, specific to the task that is run by applications running on the platform | perf.task_clock |
page_faults |
the count of page faults by applications running on the platform. This includes minor, major, invalid and other types of page faults | perf.page_faults |
context_switches |
the count of context switches by applications running on the platform | perf.context_switches |
cpu_migrations |
the count of CPU migrations, that is, where the process moved from one logical processor to another, by applications running on the platform | perf.cpu_migrations |
page_faults_min |
the count of minor page faults, that is, where the page was present in the page cache, and therefore the fault avoided loading it from storage, by applications running on the platform | perf.page_faults_min |
page_faults_maj |
the count of major page faults, that is, where the page was not present in the page cache, and therefore had to be fetched from storage, by applications running on the platform | perf.page_faults_maj |
alignment_faults |
the count of alignment faults, that is when the load or store is not aligned properly, by applications running on the platform | perf.alignment_faults |
emulation_faults |
the count of emulation faults, that is when the kernel traps on unimplemented instrucions and emulates them for user space, by applications running on the platform | perf.emulation_faults |
Devices
The final set of XML elements are all used to describe devices provided to the guest domain. All devices occur as children of the main devices
element. Since 0.1.3
...
<devices>
<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
</devices>
...
emulator
The contents of the
emulator
element specify the fully qualified path to the device model emulator binary. The capabilities XML specifies the recommended default emulator to use for each particular domain type / architecture combination.
To help users identifying devices they care about, every device can have direct child alias
element which then has name
attribute where users can store identifier for the device. The identifier has to have "ua-" prefix and must be unique within the domain. Additionally, the identifier must consist only of the following characters: [a-zA-Z0-9_-]
. Since 3.9.0
<devices>
<disk type='file'>
<alias name='ua-myDisk'/>
</disk>
<interface type='network' trustGuestRxFilters='yes'>
<alias name='ua-myNIC'/>
</interface>
...
</devices>
Hard drives, floppy disks, CDROMs
Any device that looks like a disk, be it a floppy, harddisk, cdrom, or paravirtualized driver is specified via the disk
element.
...
<devices>
<disk type='file' snapshot='external'>
<driver name="tap" type="aio" cache="default"/>
<source file='/var/lib/xen/images/fv0' startupPolicy='optional'>
<seclabel relabel='no'/>
</source>
<target dev='hda' bus='ide'/>
<iotune>
<total_bytes_sec>10000000</total_bytes_sec>
<read_iops_sec>400000</read_iops_sec>
<write_iops_sec>100000</write_iops_sec>
</iotune>
<boot order='2'/>
<encryption type='...'>
...
</encryption>
<shareable/>
<serial>
...
</serial>
</disk>
...
<disk type='network'>
<driver name="qemu" type="raw" io="threads" ioeventfd="on" event_idx="off"/>
<source protocol="sheepdog" name="image_name">
<host name="hostname" port="7000"/>
</source>
<target dev="hdb" bus="ide"/>
<boot order='1'/>
<transient/>
<address type='drive' controller='0' bus='1' unit='0'/>
</disk>
<disk type='network'>
<driver name="qemu" type="raw"/>
<source protocol="rbd" name="image_name2">
<host name="hostname" port="7000"/>
<snapshot name="snapname"/>
<config file="/path/to/file"/>
<auth username='myuser'>
<secret type='ceph' usage='mypassid'/>
</auth>
</source>
<target dev="hdc" bus="ide"/>
</disk>
<disk type='block' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdd' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="http" name="url_path" query="foo=bar&baz=flurb>
<host name="hostname" port="80"/>
<cookies>
<cookie name="test">somevalue</cookie>
</cookies>
<readahead size='65536'/>
<timeout seconds='6'/>
</source>
<target dev='hde' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="https" name="url_path">
<host name="hostname" port="443"/>
<ssl verify="no"/>
</source>
<target dev='hdf' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftp" name="url_path">
<host name="hostname" port="21"/>
</source>
<target dev='hdg' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="ftps" name="url_path">
<host name="hostname" port="990"/>
</source>
<target dev='hdh' bus='ide' tray='open'/>
<readonly/>
</disk>
<disk type='network' device='cdrom'>
<driver name='qemu' type='raw'/>
<source protocol="tftp" name="url_path">
<host name="hostname" port="69"/>
</source>
<target dev='hdi' bus='ide' tray='open' rotation_rate='7200'/>
<readonly/>
</disk>
<disk type='block' device='lun'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'>
<slices>
<slice type='storage' offset='12345' size='123'/>
</slices>
<reservations managed='no'>
<source type='unix' path='/path/to/qemu-pr-helper' mode='client'/>
</reservations>
</source>
<target dev='sda' bus='scsi' rotation_rate='1'/>
<address type='drive' controller='0' bus='0' target='3' unit='0'/>
</disk>
<disk type='block' device='disk'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'/>
<geometry cyls='16383' heads='16' secs='63' trans='lba'/>
<blockio logical_block_size='512' physical_block_size='4096'/>
<target dev='hdj' bus='ide'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='blk-pool0' volume='blk-pool0-vol0'/>
<target dev='hdk' bus='ide'/>
</disk>
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/2'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='network' device='lun'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
</source>
<target dev='sdb' bus='scsi'/>
</disk>
<disk type='network' device='disk'>
<driver name='qemu' type='raw'/>
<source protocol='nfs' name='PATH'>
<host name='example.com'/>
<identity user='USER' group='GROUP'/>
</source>
<target dev='vda' bus='virtio'/>
</disk>
<disk type='network' device='lun'>
<driver name='qemu' type='raw'/>
<source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/0'>
<host name='example.com' port='3260'/>
<initiator>
<iqn name='iqn.2013-07.com.example:client'/>
</initiator>
</source>
<target dev='sdb' bus='scsi'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:1' mode='host'/>
<target dev='vdb' bus='virtio'/>
</disk>
<disk type='volume' device='disk'>
<driver name='qemu' type='raw'/>
<source pool='iscsi-pool' volume='unit:0:0:2' mode='direct'/>
<target dev='vdc' bus='virtio'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' queues='4' queue_size='256' />
<source file='/var/lib/libvirt/images/domain.qcow'/>
<backingStore type='file'>
<format type='qcow2'/>
<source file='/var/lib/libvirt/images/snapshot.qcow'/>
<backingStore type='block'>
<format type='raw'/>
<source dev='/dev/mapper/base'/>
<backingStore/>
</backingStore>
</backingStore>
<target dev='vdd' bus='virtio'/>
</disk>
<disk type='nvme' device='disk'>
<driver name='qemu' type='raw'/>
<source type='pci' managed='yes' namespace='1'>
<address domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</source>
<target dev='vde' bus='virtio'/>
</disk>
<disk type='vhostuser' device='disk'>
<driver name='qemu' type='raw'/>
<source type='unix' path='/tmp/vhost-blk.sock'>
<reconnect enabled='yes' timeout='10'/>
</source>
<target dev='vdf' bus='virtio'/>
</disk>
</devices>
...
disk
The
disk
element is the main container for describing disks and supports the following attributes:type
Valid values are "file", "block", "dir" ( since 0.7.5 ), "network" ( since 0.8.7 ), or "volume" ( since 1.0.5 ), or "nvme" ( since 6.0.0 ), or "vhostuser" ( since 7.1.0 ) and refer to the underlying source for the disk. Since 0.0.3
device
Indicates how the disk is to be exposed to the guest OS. Possible values for this attribute are "floppy", "disk", "cdrom", and "lun", defaulting to "disk".
Using "lun" ( since 0.9.10 ) is only valid when the
type
is "block" or "network" forprotocol='iscsi'
or when thetype
is "volume" when using an iSCSI sourcepool
formode
"host" or as an NPIV virtual Host Bus Adapter (vHBA) using a Fibre Channel storage pool. Configured in this manner, the LUN behaves identically to "disk", except that generic SCSI commands from the guest are accepted and passed through to the physical device. Also note that device='lun' will only be recognized for actual raw devices, but never for individual partitions or LVM partitions (in those cases, the kernel will reject the generic SCSI commands, making it identical to device='disk'). Since 0.1.4model
Indicates the emulated device model of the disk. Typically this is indicated solely by the
bus
property but forbus
"virtio" the model can be specified further with "virtio-transitional", "virtio-non-transitional", or "virtio". See Virtio transitional devices for more details. Since 5.2.0rawio
Indicates whether the disk needs rawio capability. Valid settings are "yes" or "no" (default is "no"). If any one disk in a domain has rawio='yes', rawio capability will be enabled for all disks in the domain (because, in the case of QEMU, this capability can only be set on a per-process basis). This attribute is only valid when device is "lun". NB,
rawio
intends to confine the capability per-device, however, current QEMU implementation gives the domain process broader capability than that (per-process basis, affects all the domain disks). To confine the capability as much as possible for QEMU driver as this stage,sgio
is recommended, it's more secure thanrawio
. Since 0.9.10sgio
If supported by the hypervisor and OS, indicates whether unprivileged SG_IO commands are filtered for the disk. Valid settings are "filtered" or "unfiltered" where the default is "filtered". Only available when the
device
is 'lun'. Since 1.0.2snapshot
Indicates the default behavior of the disk during disk snapshots: "
internal
" requires a file format such as qcow2 that can store both the snapshot and the data changes since the snapshot; "external
" will separate the snapshot from the live data; "no
" means the disk will not participate in snapshots; andmanual
allows snapshotting done via an unmanaged storage provider. Read-only disks default to "no
", while the default for other disks depends on the hypervisor's capabilities. Some hypervisors allow a per-snapshot choice as well, during domain snapshot creation. Not all snapshot modes are supported; for example, enabling snapshots with a transient disk generally does not make sense. Since 0.9.5
source
Representation of the disk
source
depends on the disktype
attribute value as follows:file
The
file
attribute specifies the fully-qualified path to the file holding the disk. Since 0.0.3block
The
dev
attribute specifies the fully-qualified path to the host device to serve as the disk. Since 0.0.3dir
The
dir
attribute specifies the fully-qualified path to the directory to use as the disk. Since 0.7.5network
The
protocol
attribute specifies the protocol to access to the requested image. Possible values are "nbd", "iscsi", "rbd", "sheepdog", "gluster", "vxhs", "nfs", "http", "https", "ftp", ftps", or "tftp".For any
protocol
other thannbd
an additional attributename
is mandatory to specify which volume/image will be used.For "nbd", the
name
attribute is optional. TLS transport for NBD can be enabled by setting thetls
attribute toyes
. For the QEMU hypervisor, usage of a TLS environment can also be globally controlled on the host by thenbd_tls
andnbd_tls_x509_cert_dir
in /etc/libvirt/qemu.conf. ('tls' Since 4.5.0 ) Since 8.2.0 the optional attributetlsHostname
can be used to override the expected host name of the NBD server used for TLS certificate verification.For protocols
http
andhttps
an optional attributequery
specifies the query string. ( Since 6.2.0 )For "iscsi" ( since 1.0.4 ), the
name
attribute may include a logical unit number, separated from the target's name by a slash (e.g.,iqn.2013-07.com.example:iscsi-pool/1
). If not specified, the default LUN is zero.For "vxhs" ( since 3.8.0 ), the
name
is the UUID of the volume, assigned by the HyperScale server. Additionally, an optional attributetls
(QEMU only) can be used to control whether a VxHS block device would utilize a hypervisor configured TLS X.509 certificate environment in order to encrypt the data channel. For the QEMU hypervisor, usage of a TLS environment can also be globally controlled on the host by thevxhs_tls
andvxhs_tls_x509_cert_dir
ordefault_tls_x509_cert_dir
settings in the file /etc/libvirt/qemu.conf. Ifvxhs_tls
is enabled, then unless the domaintls
attribute is set to "no", libvirt will use the host configured TLS environment. If thetls
attribute is set to "yes", then regardless of the qemu.conf setting, TLS authentication will be attempted.Since 0.8.7
volume
The underlying disk source is represented by attributes
pool
andvolume
. Attributepool
specifies the name of the storage pool (managed by libvirt) where the disk source resides. Attributevolume
specifies the name of storage volume (managed by libvirt) used as the disk source. The value for thevolume
attribute will be the output from the "Name" column of avirsh vol-list [pool-name]
command.Use the attribute
mode
( since 1.1.1 ) to indicate how to represent the LUN as the disk source. Valid values are "direct" and "host". Ifmode
is not specified, the default is to use "host". Using "direct" as themode
value indicates to use the storage pool'ssource
elementhost
attribute as the disk source to generate the libiscsi URI (e.g. 'file=iscsi://example.com:3260/iqn.2013-07.com.example:iscsi-pool/1'). Using "host" as themode
value indicates to use the LUN's path as it shows up on host (e.g. 'file=/dev/disk/by-path/ip-example.com:3260-iscsi-iqn.2013-07.com.example:iscsi-pool-lun-1'). Using a LUN from an iSCSI source pool provides the same features as adisk
configured usingtype
'block' or 'network' anddevice
of 'lun' with respect to how the LUN is presented to and may be used by the guest. Since 1.0.5nvme
To specify disk source for NVMe disk the
source
element has the following attributes:type
The type of address specified in
address
sub-element. Currently, onlypci
value is accepted.managed
This attribute instructs libvirt to detach NVMe controller automatically on domain startup (
yes
) or expect the controller to be detached by system administrator (no
).namespace
The namespace ID which should be assigned to the domain. According to NVMe standard, namespace numbers start from 1, including.
The difference between
<disk type='nvme'>
and<hostdev/>
is that the latter is plain host device assignment with all its limitations (e.g. no live migration), while the former makes hypervisor to run the NVMe disk through hypervisor's block layer thus enabling all features provided by the layer (e.g. snapshots, domain migration, etc.). Moreover, since the NVMe disk is unbinded from its PCI driver, the host kernel storage stack is not involved (compared to passing say/dev/nvme0n1
via<disk type='block'>
and therefore lower latencies can be achieved.vhostuser
Enables the hypervisor to connect to another process using vhost-user protocol. Requires shared memory configured for the VM, for more details see
access
mode formemoryBacking
element (See Memory Backing).The
source
element has following mandatory attributes:type
The type of char device. Currently only
unix
type is supported.path
Path to the unix socket to be used as disk source.
Note that the vhost server replaces both the disk frontend and backend thus almost all of the disk properties can't be configured via the
<disk>
XML for this disk type. Additionally features such as blockjobs, incremental backups and snapshots are not supported for this disk type.
With "file", "block", and "volume", one or more optional sub-elements
seclabel
, described below (and since 0.9.9 ), can be used to override the domain security labeling policy for just that source file. (NB, for "volume" type disk,seclabel
is only valid when the specified storage volume is of 'file' or 'block' type).The
source
element may also have theindex
attribute with same semantics theindex
attribute ofbackingStore
.The
source
element may contain the following sub elements:host
When the disk
type
is "network", thesource
may have zero or morehost
sub-elements used to specify the hosts to connect. Thehost
element supports 4 attributes, viz. "name", "port", "transport" and "socket", which specify the hostname, the port number, transport type and path to socket, respectively. The meaning of this element and the number of the elements depend on the protocol attribute.Protocol Meaning Number of hosts Default port nbd a server running nbd-server only one 10809 iscsi an iSCSI server only one 3260 rbd monitor servers of RBD one or more librados default sheepdog one of the sheepdog servers (default is localhost:7000) zero or one 7000 gluster a server running glusterd daemon one or more ( Since 2.1.0 ), just one prior to that 24007 vxhs a server running Veritas HyperScale daemon only one 9999 nfs a server running Network File System only one ( Since 7.0.0 ) must be omitted gluster supports "tcp", "rdma", "unix" as valid values for the transport attribute. nbd supports "tcp" and "unix". Others only support "tcp". If nothing is specified, "tcp" is assumed. If the transport is "unix", the socket attribute specifies the path to an AF_UNIX socket. nfs only supports the use of a "tcp" transport, and does not support using a port at all so it must be omitted.
snapshot
The
name
attribute ofsnapshot
element can optionally specify an internal snapshot name to be used as the source for storage protocols. Supported for 'rbd' since 1.2.11 (QEMU only).config
The
file
attribute for theconfig
element provides a fully qualified path to a configuration file to be provided as a parameter to the client of a networked storage protocol. Supported for 'rbd' since 1.2.11 (QEMU only).auth
Since libvirt 3.9.0 , the
auth
element is supported for a disktype
"network" that is using asource
element with theprotocol
attributes "rbd" or "iscsi". If present, theauth
element provides the authentication credentials needed to access the source. It includes a mandatory attributeusername
, which identifies the username to use during authentication, as well as a sub-elementsecret
with mandatory attributetype
, to tie back to a libvirt secret object that holds the actual password or other credentials (the domain XML intentionally does not expose the password, only the reference to the object that does manage the password). Known secret types are "ceph" for Ceph RBD network sources and "iscsi" for CHAP authentication of iSCSI targets. Both will require either auuid
attribute with the UUID of the secret object or ausage
attribute matching the key that was specified in the secret object.encryption
Since libvirt 3.9.0 , the
encryption
can be a sub-element of thesource
element for encrypted storage sources. If present, specifies how the storage source is encrypted See the Storage Encryption page for more information. Note that the 'qcow' format of encryption is broken and thus is no longer supported for use with disk images. ( Since libvirt 4.5.0 )reservations
Since libvirt 4.4.0 , the
reservations
can be a sub-element of thesource
element for storage sources (QEMU driver only). If present it enables persistent reservations for SCSI based disks. The element has one mandatory attributemanaged
with accepted valuesyes
andno
. Ifmanaged
is enabled libvirt prepares and manages any resources needed. When the persistent reservations are unmanaged, then the hypervisor acts as a client and the path to the server socket must be provided in the child elementsource
, which currently accepts only the following attributes:type
with one valueunix
,path
path to the socket, and finallymode
which accepts one valueclient
specifying the role of hypervisor. It's recommended to allow libvirt manage the persistent reservations.initiator
Since libvirt 4.7.0 , the
initiator
element is supported for a disktype
"network" that is using asource
element with theprotocol
attribute "iscsi". If present, theinitiator
element provides the initiator IQN needed to access the source via mandatory attributename
.address
For disk of type
nvme
this element specifies the PCI address of the host NVMe controller. Since 6.0.0slices
The
slices
element using itsslice
sub-elements allows configuring offset and size of either the location of the image format (slice type='storage'
) inside the storage source or the guest data inside the image format container (future expansion). Theoffset
andsize
values are in bytes. Since 6.1.0ssl
For
https
andftps
accessed storage it's possible to tweak the SSL transport parameters with this element. Theverify
attribute allows to turn on or off SSL certificate validation. Supported values areyes
andno
. Since 6.2.0cookies
For
http
andhttps
accessed storage it's possible to pass one or more cookies. The cookie name and value must conform to the HTTP specification. Since 6.2.0readahead
Specifies the size of the readahead buffer for protocols which support it. (all 'curl' based drivers in qemu). The size is in bytes. Note that '0' is considered as if the value is not provided. Since 6.2.0
timeout
Specifies the connection timeout for protocols which support it. Note that '0' is considered as if the value is not provided. Since 6.2.0
identity
When using an
nfs
protocol, this is used to provide information on the configuration of the user and group. The element has two attributes,user
andgroup
. The user can provide these elements as user or group strings, or as user and group ID numbers directly if the string is formatted using a "+" at the beginning of the ID number. If either of these attributes is omitted, then that field is assumed to be the default value for the current system. If bothuser
andgroup
are intended to be default, then the entire element may be omitted.reconnect
For disk type
vhostuser
configures reconnect timeout if the connection is lost. It has two mandatory attributes:enabled
If the reconnect feature is enabled, accepts
yes
andno
timeout
The amount of seconds after which hypervisor tries to reconnect.
For a "file" or "volume" disk type which represents a cdrom or floppy (the
device
attribute), it is possible to define policy what to do with the disk if the source file is not accessible. (NB,startupPolicy
is not valid for "volume" disk unless the specified storage volume is of "file" type). This is done by thestartupPolicy
attribute ( since 0.9.7 ), accepting these values:mandatory fail if missing for any reason (the default) requisite fail if missing on boot up, drop if missing on migrate/restore/revert optional drop if missing at any start attempt Since 1.1.2 the
startupPolicy
is extended to support hard disks besides cdrom and floppy. On guest cold bootup, if a certain disk is not accessible or its disk chain is broken, with startupPolicy 'optional' the guest will drop this disk. This feature doesn't support migration currently.backingStore
This element describes the backing store used by the disk specified by sibling
source
element. Since 1.2.4. If the hypervisor driver does not support the backingStoreInput ( Since 5.10.0 ) domain feature thebackingStore
is ignored on input and only used for output to describe the detected backing chains of running domains. IfbackingStoreInput
is supported thebackingStore
is used as the backing image ofsource
or otherbackingStore
overriding any backing image information recorded in the image metadata. An emptybackingStore
element means the sibling source is self-contained and is not based on any backing store. For the detected backing chain information to be accurate, the backing format must be correctly specified in the metadata of each file of the chain (files created by libvirt satisfy this property, but using existing external files for snapshot or block copy operations requires the end user to pre-create the file correctly). The following attributes are supported inbackingStore
:type
The
type
attribute represents the type of disk used by the backing store, see disk type attribute above for more details and possible values.index
This attribute is only valid in output (and ignored on input) and it can be used to refer to a specific part of the disk chain when doing block operations (such as via the
virDomainBlockRebase
API). For example,vda[2]
refers to the backing store withindex='2'
of the disk withvda
target.
Moreover,
backingStore
supports the following sub-elements:format
The
format
element containstype
attribute which specifies the internal format of the backing store, such asraw
orqcow2
.The
format
element can containmetadata_cache
subelement, which has identical semantics to the identically named subelement ofdriver
of adisk
.source
This element has the same structure as the
source
element indisk
. It specifies which file, device, or network location contains the data of the described backing store.backingStore
If the backing store is not self-contained, the next element in the chain is described by nested
backingStore
element.
mirror
This element is present if the hypervisor has started a long-running block job operation, where the mirror location in the
source
sub-element will eventually have the same contents as the source, and with the file format in the sub-elementformat
(which might differ from the format of the source). The details of thesource
sub-element are determined by thetype
attribute of the mirror, similar to what is done for the overalldisk
device element. Thejob
attribute mentions which API started the operation ("copy" for thevirDomainBlockRebase
API, or "active-commit" for thevirDomainBlockCommit
API), since 1.2.7 . The attributeready
, if present, tracks progress of the job:yes
if the disk is known to be ready to pivot, or, since 1.2.7 ,abort
orpivot
if the job is in the process of completing. Ifready
is not present, the disk is probably still copying. For now, this element only valid in output; it is ignored on input. Thesource
sub-element exists for all two-phase jobs since 1.2.6 . Older libvirt supported only block copy to a file, since 0.9.12 ; for compatibility with older clients, such jobs include redundant information in the attributesfile
andformat
in themirror
element.target
The
target
element controls the bus / device under which the disk is exposed to the guest OS. Thedev
attribute indicates the "logical" device name. The actual device name specified is not guaranteed to map to the device name in the guest OS. Treat it as a device ordering hint. The optionalbus
attribute specifies the type of disk device to emulate; possible values are driver specific, with typical values being "ide", "scsi", "virtio", "xen", "usb", "sata", or "sd" "sd" since 1.1.2 . If omitted, the bus type is inferred from the style of the device name (e.g. a device named 'sda' will typically be exported using a SCSI bus). The optional attributetray
indicates the tray status of the removable disks (i.e. CDROM or Floppy disk), the value can be either "open" or "closed", defaults to "closed". NB, the value oftray
could be updated while the domain is running. The optional attributeremovable
sets the removable flag for USB disks, and its value can be either "on" or "off", defaulting to "off". The optional attributerotation_rate
sets the rotation rate of the storage for disks on a SCSI, IDE, or SATA bus. Values in the range 1025 to 65534 are used to indicate rotational media speed in revolutions per minute. A value of one is used to indicate solid state, or otherwise non-rotational, storage. These values are not required to match the values of the underlying host storage. Since 0.0.3;bus
attribute since 0.4.3;tray
attribute since 0.9.11; "usb" attribute value since after 0.4.4; "sata" attribute value since 0.9.7; "removable" attribute value since 1.1.3; "rotation_rate" attribute value since 7.3.0iotune
The optional
iotune
element provides the ability to provide additional per-device I/O tuning, with values that can vary for each device (contrast this to theblkiotune
element (See Block I/O Tuning), which applies globally to the domain). Currently, the only tuning available is Block I/O throttling for qemu. This element has optional sub-elements; any sub-element not specified or given with a value of 0 implies no limit. Since 0.9.8total_bytes_sec
The optional
total_bytes_sec
element is the total throughput limit in bytes per second. This cannot appear withread_bytes_sec
orwrite_bytes_sec
.read_bytes_sec
The optional
read_bytes_sec
element is the read throughput limit in bytes per second.write_bytes_sec
The optional
write_bytes_sec
element is the write throughput limit in bytes per second.total_iops_sec
The optional
total_iops_sec
element is the total I/O operations per second. This cannot appear withread_iops_sec
orwrite_iops_sec
.read_iops_sec
The optional
read_iops_sec
element is the read I/O operations per second.write_iops_sec
The optional
write_iops_sec
element is the write I/O operations per second.total_bytes_sec_max
The optional
total_bytes_sec_max
element is the maximum total throughput limit in bytes per second. This cannot appear withread_bytes_sec_max
orwrite_bytes_sec_max
.read_bytes_sec_max
The optional
read_bytes_sec_max
element is the maximum read throughput limit in bytes per second.write_bytes_sec_max
The optional
write_bytes_sec_max
element is the maximum write throughput limit in bytes per second.total_iops_sec_max
The optional
total_iops_sec_max
element is the maximum total I/O operations per second. This cannot appear withread_iops_sec_max
orwrite_iops_sec_max
.read_iops_sec_max
The optional
read_iops_sec_max
element is the maximum read I/O operations per second.write_iops_sec_max
The optional
write_iops_sec_max
element is the maximum write I/O operations per second.size_iops_sec
The optional
size_iops_sec
element is the size of I/O operations per second.Throughput limits since 1.2.11 and QEMU 1.7
group_name
The optional
group_name
provides the cability to share I/O throttling quota between multiple drives. This prevents end-users from circumventing a hosting provider's throttling policy by splitting 1 large drive in N small drives and getting N times the normal throttling quota. Any name may be used.group_name since 3.0.0 and QEMU 2.4
total_bytes_sec_max_length
The optional
total_bytes_sec_max_length
element is the maximum duration in seconds for thetotal_bytes_sec_max
burst period. Only valid when thetotal_bytes_sec_max
is set.read_bytes_sec_max_length
The optional
read_bytes_sec_max_length
element is the maximum duration in seconds for theread_bytes_sec_max
burst period. Only valid when theread_bytes_sec_max
is set.write_bytes_sec_max
The optional
write_bytes_sec_max_length
element is the maximum duration in seconds for thewrite_bytes_sec_max
burst period. Only valid when thewrite_bytes_sec_max
is set.total_iops_sec_max_length
The optional
total_iops_sec_max_length
element is the maximum duration in seconds for thetotal_iops_sec_max
burst period. Only valid when thetotal_iops_sec_max
is set.read_iops_sec_max_length
The optional
read_iops_sec_max_length
element is the maximum duration in seconds for theread_iops_sec_max
burst period. Only valid when theread_iops_sec_max
is set.write_iops_sec_max
The optional
write_iops_sec_max_length
element is the maximum duration in seconds for thewrite_iops_sec_max
burst period. Only valid when thewrite_iops_sec_max
is set.Throughput length since 2.4.0 and QEMU 2.6
driver
The optional driver element allows specifying further details related to the hypervisor driver used to provide the disk. Since 0.1.8
If the hypervisor supports multiple backend drivers, then the
name
attribute selects the primary backend driver name, while the optionaltype
attribute provides the sub-type. For example, xen supports a name of "tap", "tap2", "phy", or "file", with a type of "aio", while qemu only supports a name of "qemu", but multiple types including "raw", "bochs", "qcow2", and "qed".The optional
cache
attribute controls the cache mechanism, possible values are "default", "none", "writethrough", "writeback", "directsync" (like "writethrough", but it bypasses the host page cache) and "unsafe" (host may cache all disk io, and sync requests from guest are ignored). Since 0.6.0, "directsync" since 0.9.5, "unsafe" since 0.9.7The optional
error_policy
attribute controls how the hypervisor will behave on a disk read or write error, possible values are "stop", "report", "ignore", and "enospace". Since 0.8.0, "report" since 0.9.7 The default is left to the discretion of the hypervisor. There is also an optionalrerror_policy
that controls behavior for read errors only. Since 0.9.7 . If no rerror_policy is given, error_policy is used for both read and write errors. If rerror_policy is given, it overrides theerror_policy
for read errors. Also note that "enospace" is not a valid policy for read errors, so iferror_policy
is set to "enospace" and norerror_policy
is given, the read error policy will be left at its default.The optional
io
attribute controls specific policies on I/O; qemu guests support "threads" and "native" Since 0.8.8 , io_uring Since 6.3.0 (QEMU 5.0) .The optional
ioeventfd
attribute allows users to set domain I/O asynchronous handling for disk device. The default is left to the discretion of the hypervisor. Accepted values are "on" and "off". Enabling this allows qemu to execute VM while a separate thread handles I/O. Typically guests experiencing high system CPU utilization during I/O will benefit from this. On the other hand, on overloaded host it could increase guest I/O latency. Since 0.9.3 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.The optional
event_idx
attribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interrupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.The optional
copy_on_read
attribute controls whether to copy read backing file into the image file. The value can be either "on" or "off". Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the backing file is over a slow network. By default copy-on-read is off. Since 0.9.10 (QEMU and KVM only)The optional
discard
attribute controls whether discard requests (also known as "trim" or "unmap") are ignored or passed to the filesystem. The value can be either "unmap" (allow the discard request to be passed) or "ignore" (ignore the discard request). Since 1.0.6 (QEMU and KVM only)The optional
detect_zeroes
attribute controls whether to detect zero write requests. The value can be "off", "on" or "unmap". First two values turn the detection off and on, respectively. The third value ("unmap") turns the detection on and additionally tries to discard such areas from the image based on the value ofdiscard
above (it will act as "on" ifdiscard
is set to "ignore"). NB enabling the detection is a compute intensive operation, but can save file space and/or time on slow media. Since 2.0.0The optional
iothread
attribute assigns the disk to an IOThread as defined by the range for the domainiothreads
value. (See IOThreads Allocation). Multiple disks may be assigned to the same IOThread and are numbered from 1 to the domain iothreads value. Available for a disk devicetarget
configured to use "virtio"bus
and "pci" or "ccw"address
types. Since 1.2.8 (QEMU 2.1)The optional
queues
attribute specifies the number of virt queues for virtio-blk. ( Since 3.9.0 )The optional
queue_size
attribute specifies the size of each virt queue for virtio-blk. ( Since 7.8.0 )For virtio disks, Virtio-related options can also be set. ( Since 3.5.0 )
The optional
metadata_cache
subelement controls aspects related to the format specific caching of storage image metadata. Note that this setting applies only on the top level image; the identically named subelement ofbackingStore
'sformat
element can be used to specify cache settings for the backing image.Since 7.0.0 the maximum size of the metadata cache of
qcow2
format driver of theqemu
hypervisor can be controlled via themax_size
subelement (see example below).In the majority of cases the default configuration used by the hypervisor is sufficient so modifying this setting should not be necessary. For specifics on how the metadata cache of
qcow2
inqemu
behaves refer to theqemu
qcow2 cache docsExample:
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'>
<metadata_cache>
<max_size unit='bytes'>1234</max_size>
</metadata_cache>
</driver>
<source file='/var/lib/libvirt/images/domain.qcow'/>
<backingStore type='file'>
<format type='qcow2'>
<metadata_cache>
<max_size unit='bytes'>1234</max_size>
</metadata_cache>
</format>
<source file='/var/lib/libvirt/images/snapshot.qcow'/>
<backingStore/>
</backingStore>
<target dev='vdd' bus='virtio'/>
</disk>
backenddomain
The optional
backenddomain
element allows specifying a backend domain (aka driver domain) hosting the disk. Use thename
attribute to specify the backend domain name. Since 1.2.13 (Xen only)boot
Specifies that the disk is bootable. The
order
attribute determines the order in which devices will be tried during boot sequence. On the S390 architecture only the first boot device is used. The optionalloadparm
attribute is an 8 character string which can be queried by guests on S390 via sclp or diag 308. Linux guests on S390 can useloadparm
to select a boot entry. Since 3.5.0 The per-deviceboot
elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8encryption
Starting with libvirt 3.9.0 the
encryption
element is preferred to be a sub-element of thesource
element. If present, specifies how the volume is encrypted using "qcow". See the Storage Encryption page for more information.readonly
If present, this indicates the device cannot be modified by the guest. For now, this is the default for disks with attribute
device='cdrom'
.shareable
If present, this indicates the device is expected to be shared between domains (assuming the hypervisor and OS support this), which means that caching should be deactivated for that device.
transient
If present, this indicates that changes to the device contents should be reverted automatically when the guest exits. With some hypervisors, marking a disk transient prevents the domain from participating in migration, snapshots, or blockjobs. Only supported in vmx hypervisor (Since 0.9.5) and
qemu
hypervisor (Since 6.9.0).In cases where the source image of the
<transient/>
disk is supposed to be shared between multiple concurrently running VMs the optionalshareBacking
attribute should be set toyes
. Note that hypervisor drivers may need to hotplug such disk and thus it works only with configurations supporting hotplug. Since 7.4.0serial
If present, this specify serial number of virtual hard drive. For example, it may look like
<serial>WD-WMAP9A966149</serial>
. Not supported for scsi-block devices, that is those using disktype
'block' usingdevice
'lun' onbus
'scsi'. Since 0.7.1Note that depending on hypervisor and device type the serial number may be truncated silently. IDE/SATA devices are commonly limited to 20 characters. SCSI devices depending on hypervisor version are limited to 20, 36 or 247 characters.
Hypervisors may also start rejecting overly long serials instead of truncating them in the future so it's advised to avoid the implicit truncation by testing the desired serial length range with the desired device and hypervisor combination.
wwn
If present, this element specifies the WWN (World Wide Name) of a virtual hard disk or CD-ROM drive. It must be composed of 16 hexadecimal digits. Since 0.10.1
vendor
If present, this element specifies the vendor of a virtual hard disk or CD-ROM device. It must not be longer than 8 printable characters. Since 1.0.1
product
If present, this element specifies the product of a virtual hard disk or CD-ROM device. It must not be longer than 16 printable characters. Since 1.0.1
address
If present, the
address
element ties the disk to a given slot of a controller (the actual<controller>
device can often be inferred by libvirt, although it can be be explicitly specified. See Controllers). Thetype
attribute is mandatory, and is typically "pci" or "drive". For a "pci" controller, additional attributes forbus
,slot
, andfunction
must be present, as well as optionaldomain
andmultifunction
. Multifunction defaults to 'off'; any other value requires QEMU 0.1.3 and libvirt 0.9.7 . For a "drive" controller, additional attributescontroller
,bus
,target
( libvirt 0.9.11 ), andunit
are available, each defaulting to 0.auth
Starting with libvirt 3.9.0 the
auth
element is preferred to be a sub-element of thesource
element. The element is still read and managed as adisk
sub-element. It is invalid to useauth
as both a sub-element ofdisk
andsource
. Theauth
element was introduced as adisk
sub-element in libvirt 0.9.7.geometry
The optional
geometry
element provides the ability to override geometry settings. This mostly useful for S390 DASD-disks or older DOS-disks. 0.10.0cyls
The
cyls
attribute is the number of cylinders.heads
The
heads
attribute is the number of heads.secs
The
secs
attribute is the number of sectors per track.trans
The optional
trans
attribute is the BIOS-Translation-Modus (none, lba or auto)
blockio
If present, the
blockio
element allows to override any of the block device properties listed below. Since 0.10.2 (QEMU and KVM)logical_block_size
The logical block size the disk will report to the guest OS. For Linux this would be the value returned by the BLKSSZGET ioctl and describes the smallest units for disk I/O.
physical_block_size
The physical block size the disk will report to the guest OS. For Linux this would be the value returned by the BLKPBSZGET ioctl and describes the disk's hardware sector size which can be relevant for the alignment of disk data.
Filesystems
A directory on the host that can be accessed directly from the guest. since 0.3.3, since 0.8.5 for QEMU/KVM
...
<devices>
<filesystem type='template'>
<source name='my-vm-template'/>
<target dir='/'/>
</filesystem>
<filesystem type='mount' accessmode='passthrough' multidevs='remap'>
<driver type='path' wrpolicy='immediate'/>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='mount' accessmode='mapped' fmode='644' dmode='755'>
<driver type='path'/>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='file' accessmode='passthrough'>
<driver type='loop' format='raw'/>
<source file='/export/to/guest.img'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='mount' accessmode='passthrough'>
<driver type='virtiofs' queue='1024'/>
<binary path='/usr/libexec/virtiofsd' xattr='on'>
<cache mode='always'/>
<sandbox mode='namespace'/>
<lock posix='on' flock='on'/>
</binary>
<source dir='/path'/>
<target dir='mount_tag'/>
</filesystem>
<filesystem type='mount'>
<driver type='virtiofs' queue='1024'/>
<source socket='/tmp/sock'/>
<target dir='tag'/>
</filesystem>
...
</devices>
...
filesystem
The filesystem attribute
type
specifies the type of thesource
. The possible values are:mount
A host directory to mount in the guest. Used by LXC, OpenVZ (since 0.6.2) and QEMU/KVM (since 0.8.5) . This is the default
type
if one is not specified. This mode also has an optional sub-elementdriver
, with an attributetype='path'
ortype='handle'
(since 0.9.7) . The driver block has an optional attributewrpolicy
that further controls interaction with the host page cache; omitting the attribute gives default behavior, while the valueimmediate
means that a host writeback is immediately triggered for all pages touched during a guest file write operation (since 0.9.10) . Since 6.2.0 ,type='virtiofs'
is also supported. Using virtiofs requires setting up shared memory, see the guide: Virtiofstemplate
OpenVZ filesystem template. Only used by OpenVZ driver.
file
A host file will be treated as an image and mounted in the guest. The filesystem format will be autodetected. Only used by LXC driver.
block
A host block device to mount in the guest. The filesystem format will be autodetected. Only used by LXC driver (since 0.9.5) .
ram
An in-memory filesystem, using memory from the host OS. The source element has a single attribute
usage
which gives the memory usage limit in KiB, unless units are specified by theunits
attribute. Only used by LXC driver. (since 0.9.13)bind
A directory inside the guest will be bound to another directory inside the guest. Only used by LXC driver (since 0.9.13)
The filesystem element has an optional attribute
accessmode
which specifies the security mode for accessing the source (since 0.8.5) . Currently this only works withtype='mount'
for the QEMU/KVM driver. For driver typevirtiofs
, onlypassthrough
is supported. For other driver types, the possible values are:passthrough
The
source
is accessed with the permissions of the user inside the guest. This is the defaultaccessmode
if one is not specified. More infomapped
The
source
is accessed with the permissions of the hypervisor (QEMU process). More infosquash
Similar to 'passthrough', the exception is that failure of privileged operations like 'chown' are ignored. This makes a passthrough-like mode usable for people who run the hypervisor as non-root. More info
Since 5.2.0 , the filesystem element has an optional attribute
model
with supported values "virtio-transitional", "virtio-non-transitional", or "virtio". See Virtio transitional devices for more details.The filesystem element has optional attributes
fmode
anddmode
. These two attributes control the creation mode for files and directories when used with themapped
value foraccessmode
(since 6.10.0, requires QEMU 2.10 ). If not specified, QEMU creates files with mode600
and directories with mode700
. The setuid, setgid, and sticky bit are unsupported.The filesystem element has an optional attribute
multidevs
which specifies how to deal with a filesystem export containing more than one device, in order to avoid file ID collisions on guest when using 9pfs ( since 6.3.0, requires QEMU 4.2 ). This attribute is not available for virtiofs. The possible values are:default
Use QEMU's default setting (which currently is
warn
).remap
This setting allows guest to access multiple devices per export without encountering misbehaviours. Inode numbers from host are automatically remapped on guest to actively prevent file ID collisions if guest accesses one export containing multiple devices.
forbid
Only allow to access one device per export by guest. Attempts to access additional devices on the same export will cause the individual filesystem access by guest to fail with an error and being logged (once) as error on host side.
warn
This setting resembles the behaviour of 9pfs prior to QEMU 4.2, that is no action is performed to prevent any potential file ID collisions if an export contains multiple devices, with the only exception: a warning is logged (once) on host side now. This setting may lead to misbehaviours on guest side if more than one device is exported per export, due to the potential file ID collisions this may cause on guest side in that case.
driver
The optional driver element allows specifying further details related to the hypervisor driver used to provide the filesystem. Since 1.0.6
- If the hypervisor supports multiple backend drivers, then the
type
attribute selects the primary backend driver name, while theformat
attribute provides the format type. For example, LXC supports a type of "loop", with a format of "raw" or "nbd" with any format. QEMU supports a type of "path" or "handle", but no formats. Virtuozzo driver supports a type of "ploop" with a format of "ploop". - For virtio-backed devices, Virtio-related options can also be set. ( Since 3.5.0 )
- For
virtiofs
, thequeue
attribute can be used to specify the queue size (i.e. how many requests can the queue fit). ( Since 6.2.0 )
- If the hypervisor supports multiple backend drivers, then the
binary
The optional
binary
element can tune the options for virtiofsd. All of the following attributes and elements are optional. The attributepath
can be used to override the path to the daemon. Attributexattr
enables the use of filesystem extended attributes. Caching can be tuned via thecache
element, possiblemode
values beingnone
andalways
. Locking can be controlled via thelock
element - attributesposix
andflock
both accepting valueson
oroff
. ( Since 6.2.0 ) The sandboxing method used by virtiofsd can be configured with thesandbox
element, possiblemode
values beingnamespace
andchroot
, see the virtiofsd documentation for more details. ( Since 7.2.0 )source
The resource on the host that is being accessed in the guest. The
name
attribute must be used withtype='template'
, and thedir
attribute must be used withtype='mount'
. Forvirtiofs
, thesocket
attribute can be used to connect to a virtiofsd daemon launched outside of libvirt. In that case, thetarget
element does not apply and neither do most virtiofs-related options, since they are controlled by virtiofsd, not libvirtd. Theusage
attribute is used withtype='ram'
to set the memory limit in KiB, unless units are specified by theunits
attribute.target
Where the
source
can be accessed in the guest. For most drivers this is an automatic mount point, but for QEMU/KVM this is merely an arbitrary string tag that is exported to the guest as a hint for where to mount.readonly
Enables exporting filesystem as a readonly mount for guest, by default read-write access is given (currently only works for QEMU/KVM driver).
space_hard_limit
Maximum space available to this guest's filesystem. Since 0.9.13
space_soft_limit
Maximum space available to this guest's filesystem. The container is permitted to exceed its soft limits for a grace period of time. Afterwards the hard limit is enforced. Since 0.9.13
Device Addresses
Many devices have an optional <address>
sub-element to describe where the device is placed on the virtual bus presented to the guest. If an address (or any optional attribute within an address) is omitted on input, libvirt will generate an appropriate address; but an explicit address is required if more control over layout is required. See below for device examples including an address element.
Every address has a mandatory attribute type
that describes which bus the device is on. The choice of which address to use for a given device is constrained in part by the device and the architecture of the guest. For example, a <disk>
device uses type='drive'
, while a <console>
device would use type='pci'
on i686 or x86_64 guests, or type='spapr-vio'
on PowerPC64 pseries guests. Each address type has further optional attributes that control where on the bus the device will be placed:
pci
PCI addresses have the following additional attributes:
domain
(a 2-byte hex integer, not currently used by qemu),bus
(a hex value between 0 and 0xff, inclusive),slot
(a hex value between 0x0 and 0x1f, inclusive), andfunction
(a value between 0 and 7, inclusive). Also available is themultifunction
attribute, which controls turning on the multifunction bit for a particular slot/function in the PCI control register ( since 0.9.7, requires QEMU 0.13 ).multifunction
defaults to 'off', but should be set to 'on' for function 0 of a slot that will have multiple functions used. ( Since 4.10.0 ), PCI address extensions depending on the architecture are supported. For example, PCI addresses for S390 guests will have azpci
child element, with two attributes:uid
(a hex value between 0x0001 and 0xffff, inclusive), andfid
(a hex value between 0x00000000 and 0xffffffff, inclusive) used by PCI devices on S390 for User-defined Identifiers and Function Identifiers. Since 1.3.5 , some hypervisor drivers may accept an<address type='pci'/>
element with no other attributes as an explicit request to assign a PCI address for the device rather than some other type of address that may also be appropriate for that same device (e.g. virtio-mmio). The relationship between the PCI addresses configured in the domain XML and those seen by the guest OS can sometime seem confusing: a separate document describes how PCI addresses work in more detail.drive
Drive addresses have the following additional attributes:
controller
(a 2-digit controller number),bus
(a 2-digit bus number),target
(a 2-digit target number), andunit
(a 2-digit unit number on the bus).virtio-serial
Each virtio-serial address has the following additional attributes:
controller
(a 2-digit controller number),bus
(a 2-digit bus number), andslot
(a 2-digit slot within the bus).ccid
A CCID address, for smart-cards, has the following additional attributes:
bus
(a 2-digit bus number), andslot
attribute (a 2-digit slot within the bus). Since 0.8.8.usb
USB addresses have the following additional attributes:
bus
(a hex value between 0 and 0xfff, inclusive), andport
(a dotted notation of up to four octets, such as 1.2 or 2.1.3.1).spapr-vio
On PowerPC pseries guests, devices can be assigned to the SPAPR-VIO bus. It has a flat 32-bit address space; by convention, devices are generally assigned at a non-zero multiple of 0x00001000, but other addresses are valid and permitted by libvirt. Each address has the following additional attribute:
reg
(the hex value address of the starting register). Since 0.9.9.ccw
S390 guests with a
machine
value of s390-ccw-virtio use the native CCW bus for I/O devices. CCW bus addresses have the following additional attributes:cssid
(a hex value between 0 and 0xfe, inclusive),ssid
(a value between 0 and 3, inclusive) anddevno
(a hex value between 0 and 0xffff, inclusive). Partially specified bus addresses are not allowed. If omitted, libvirt will assign a free bus address with cssid=0xfe and ssid=0. Virtio-ccw devices must have their cssid set to 0xfe. Since 1.0.4virtio-mmio
This places the device on the virtio-mmio transport, which is currently only available for some
armv7l
andaarch64
virtual machines. virtio-mmio addresses do not have any additional attributes. Since 1.1.3 If the guest architecture isaarch64
and the machine type isvirt
, libvirt will automatically assign PCI addresses to devices; however, the presence of a single device with virtio-mmio address in the guest configuration will cause libvirt to assign virtio-mmio addresses to all further devices. Since 3.0.0isa
ISA addresses have the following additional attributes:
iobase
andirq
. Since 1.2.1unassigned
For PCI hostdevs,
<address type='unassigned'/>
allows the admin to include a PCI hostdev in the domain XML definition, without making it available for the guest. This allows for configurations in which Libvirt manages the device as a regular PCI hostdev, regardless of whether the guest will have access to it.<address type='unassigned'/>
is an invalid address type for all other device types. Since 6.0.0
Virtio-related options
QEMU's virtio devices have some attributes related to the virtio transport under the driver
element: The iommu
attribute enables the use of emulated IOMMU by the device. The attribute ats
controls the Address Translation Service support for PCIe devices. This is needed to make use of IOTLB support (see IOMMU device). Possible values are on
or off
. Since 3.5.0
The attribute packed
controls if QEMU should try to use packed virtqueues. Compared to regular split queues, packed queues consist of only a single descriptor ring replacing available and used ring, index and descriptor buffer. This can result in better cache utilization and performance. If packed virtqueues are actually used depends on the feature negotiation between QEMU, vhost backends and guest drivers. Possible values are on
or off
. Since 6.3.0 (QEMU and KVM only)
This optional attribute page_per_vq
controls the layout of the notification capabilities exposed to the guest. When enabled, each virtio queue will have a dedicated page on the device BAR exposed to the guest. It is recommended to be used when vDPA is enabled on the hypervisor, as it enables mapping the notification area to the physical device, which is only supported in page granularity. The default is determined by QEMU. Since 7.9.0 (QEMU 2.8) Note: In general you should leave this option alone, unless you are very certain you know what you are doing.
Virtio transitional devices
Since 5.2.0 , some of QEMU's virtio devices, when used with PCI/PCIe machine types, accept the following model
values:
virtio-transitional
This device can work both with virtio 0.9 and virtio 1.0 guest drivers, so it's the best choice when compatibility with older guest operating systems is desired. libvirt will plug the device into a conventional PCI slot.
virtio-non-transitional
This device can only work with virtio 1.0 guest drivers, and it's the recommended option unless compatibility with older guest operating systems is necessary. libvirt will plug the device into either a PCI Express slot or a conventional PCI slot based on the machine type, resulting in a more optimized PCI topology.
virtio
This device will work like a
virtio-non-transitional
device when plugged into a PCI Express slot, and like avirtio-transitional
device otherwise; libvirt will pick one or the other based on the machine type. This is the best choice when compatibility with libvirt versions older than 5.2.0 is necessary, but it's otherwise not recommended to use it.
While the information outlined above applies to most virtio devices, there are a few exceptions:
- for SCSI controllers, there is no
virtio
model available due to historical reasons: usevirtio-scsi
instead, which behaves the same asvirtio
does for other devices. Bothvirtio-transitional
andvirtio-non-transitional
work with SCSI controllers; - some devices, such as GPUs and input devices (keyboard, tablet and mouse), are only defined in the virtio 1.0 spec and as such don't have a transitional variant: the only accepted model is
virtio
, which will result in a non-transitional device.
For more details see the qemu patch posting and the virtio-1.0 spec.
Controllers
Depending on the guest architecture, some device buses can appear more than once, with a group of virtual devices tied to a virtual controller. Normally, libvirt can automatically infer such controllers without requiring explicit XML markup, but sometimes it is necessary to provide an explicit controller element, notably when planning the PCI topology for guests where device hotplug is expected.
...
<devices>
<controller type='ide' index='0'/>
<controller type='virtio-serial' index='0' ports='16' vectors='4'/>
<controller type='virtio-serial' index='1'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
</controller>
<controller type='scsi' index='0' model='virtio-scsi'>
<driver iothread='4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
</controller>
<controller type='xenbus' maxGrantFrames='64' maxEventChannels='2047'/>
...
</devices>
...
Each controller has a mandatory attribute type
, which must be one of 'ide', 'fdc', 'scsi', 'sata', 'usb', 'ccid', 'virtio-serial' or 'pci', and a mandatory attribute index
which is the decimal integer describing in which order the bus controller is encountered (for use in controller
attributes of <address>
elements). Since 1.3.5 the index is optional; if not specified, it will be auto-assigned to be the lowest unused index for the given controller type. Some controller types have additional attributes that control specific features, such as:
virtio-serial
The
virtio-serial
controller has two additional optional attributesports
andvectors
, which control how many devices can be connected through the controller. Since 5.2.0 , it supports an optional attributemodel
which can be 'virtio', 'virtio-transitional', or 'virtio-non-transitional'. See Virtio transitional devices for more details.scsi
A
scsi
controller has an optional attributemodel
, which is one of 'auto', 'buslogic', 'ibmvscsi', 'lsilogic', 'lsisas1068', 'lsisas1078', 'virtio-scsi', 'vmpvscsi', 'virtio-transitional', 'virtio-non-transitional', 'ncr53c90' (as builtin implicit controller only), 'am53c974', 'dc390'. See Virtio transitional devices for more details.usb
A
usb
controller has an optional attributemodel
, which is one of "piix3-uhci", "piix4-uhci", "ehci", "ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3", "vt82c686b-uhci", "pci-ohci", "nec-xhci", "qusb1" (xen pvusb with qemu backend, version 1.1), "qusb2" (xen pvusb with qemu backend, version 2.0) or "qemu-xhci". Additionally, since 0.10.0 , if the USB bus needs to be explicitly disabled for the guest,model='none'
may be used. Since 1.0.5 , no default USB controller will be built on s390. Since 1.3.5 , USB controllers accept aports
attribute to configure how many devices can be connected to the controller.ide
Since 3.10.0 for the vbox driver, the
ide
controller has an optional attributemodel
, which is one of "piix3", "piix4" or "ich6".xenbus
Since 5.2.0 , the
xenbus
controller has an optional attributemaxGrantFrames
, which specifies the maximum number of grant frames the controller makes available for connected devices. Since 6.3.0 , the xenbus controller supports the optionalmaxEventChannels
attribute, which specifies maximum number of event channels (PV interrupts) that can be used by the guest.
Note: The PowerPC64 "spapr-vio" addresses do not have an associated controller.
For controllers that are themselves devices on a PCI or USB bus, an optional sub-element <address>
can specify the exact relationship of the controller to its master bus, with semantics described in the Device Addresses section.
An optional sub-element driver
can specify the driver specific options:
queues
The optional
queues
attribute specifies the number of queues for the controller. For best performance, it's recommended to specify a value matching the number of vCPUs. Since 1.0.5 (QEMU and KVM only)cmd_per_lun
The optional
cmd_per_lun
attribute specifies the maximum number of commands that can be queued on devices controlled by the host. Since 1.2.7 (QEMU and KVM only)max_sectors
The optional
max_sectors
attribute specifies the maximum amount of data in bytes that will be transferred to or from the device in a single command. The transfer length is measured in sectors, where a sector is 512 bytes. Since 1.2.7 (QEMU and KVM only)ioeventfd
The optional
ioeventfd
attribute specifies whether the controller should use I/O asynchronous handling or not. Accepted values are "on" and "off". Since 1.2.18iothread
Supported for controller type
scsi
using modelvirtio-scsi
foraddress
typespci
andccw
since 1.3.5 (QEMU 2.4) . The optionaliothread
attribute assigns the controller to an IOThread as defined by the range for the domainiothreads
(See IOThreads Allocation). Each SCSIdisk
assigned to use the specifiedcontroller
will utilize the same IOThread. If a specific IOThread is desired for a specific SCSIdisk
, then multiple controllers must be defined each having a specificiothread
value. Theiothread
value must be within the range 1 to the domain iothreads value.- virtio options
For virtio controllers, Virtio-related options can also be set. ( Since 3.5.0 )
USB companion controllers have an optional sub-element <master>
to specify the exact relationship of the companion to its master controller. A companion controller is on the same bus as its master, so the companion index
value should be equal. Not all controller models can be used as companion controllers and libvirt might provide some sensible defaults (settings of master startport
and function
of an address) for some particular models. Preferred companion controllers are ich-uhci[123]
.
...
<devices>
<controller type='usb' index='0' model='ich9-ehci1'>
<address type='pci' domain='0' bus='0' slot='4' function='7'/>
</controller>
<controller type='usb' index='0' model='ich9-uhci1'>
<master startport='0'/>
<address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/>
</controller>
...
</devices>
...
PCI controllers have an optional model
attribute; possible values for this attribute are
pci-root
,pci-bridge
( since 1.0.5 )pcie-root
,dmi-to-pci-bridge
( since 1.1.2 )pcie-root-port
,pcie-switch-upstream-port
,pcie-switch-downstream-port
( since 1.2.19 )pci-expander-bus
,pcie-expander-bus
( since 1.3.4 )pcie-to-pci-bridge
( since 4.3.0 )
The root controllers (pci-root
and pcie-root
) have an optional pcihole64
element specifying how big (in kilobytes, or in the unit specified by pcihole64
's unit
attribute) the 64-bit PCI hole should be. Some guests (like Windows XP or Windows Server 2003) might crash when QEMU and Seabios are recent enough to support 64-bit PCI holes, unless this is disabled (set to 0). Since 1.1.2 (QEMU only)
PCI controllers also have an optional subelement <model>
with an attribute name
. The name attribute holds the name of the specific device that qemu is emulating (e.g. "i82801b11-bridge") rather than simply the class of device ("pcie-to-pci-bridge", "pci-bridge"), which is set in the controller element's model attribute. In almost all cases, you should not manually add a <model>
subelement to a controller, nor should you modify one that is automatically generated by libvirt. Since 1.2.19 (QEMU only).
PCI controllers also have an optional subelement <target>
with the attributes and subelements listed below. These are configurable items that 1) are visible to the guest OS so must be preserved for guest ABI compatibility, and 2) are usually left to default values or derived automatically by libvirt. In almost all cases, you should not manually add a <target>
subelement to a controller, nor should you modify the values in the those that are automatically generated by libvirt. Since 1.2.19 (QEMU only).
chassisNr
PCI controllers that have attribute model="pci-bridge", can also have a
chassisNr
attribute in the<target>
subelement, which is used to control QEMU's "chassis_nr" option for the pci-bridge device (normally libvirt automatically sets this to the same value as the index attribute of the pci controller). If set, chassisNr must be between 1 and 255.chassis
pcie-root-port and pcie-switch-downstream-port controllers can also have a
chassis
attribute in the<target>
subelement, which is used to set the controller's "chassis" configuration value, which is visible to the virtual machine. If set, chassis must be between 0 and 255.port
pcie-root-port and pcie-switch-downstream-port controllers can also have a
port
attribute in the<target>
subelement, which is used to set the controller's "port" configuration value, which is visible to the virtual machine. If set, port must be between 0 and 255.hotplug
pci-root (Since 7.9.0), pcie-root-port (Since 6.3.0) and pcie-switch-downstream-port controllers (Since 6.3.0) can also have a
hotplug
attribute in the<target>
subelement, which is used to disable hotplug/unplug of devices on a particular controller. For the pci-root controller, the setting affects the ACPI based hotplug. For the rest, the setting affects both ACPI based hotplug as well as PCIE native hotplug. The default setting ofhotplug
ison
; it should be set tooff
to disable hotplug/unplug of devices on a particular controller.busNr
pci-expander-bus and pcie-expander-bus controllers can have an optional
busNr
attribute (1-254). This will be the bus number of the new bus; All bus numbers between that specified and 255 will be available only for assignment to PCI/PCIe controllers plugged into the hierarchy starting with this expander bus, and bus numbers less than the specified value will be available to the next lower expander-bus (or the root-bus if there are no lower expander buses). If you do not specify a busNumber, libvirt will find the lowest existing busNumber in all other expander buses (or use 256 if there are no others) and auto-assign the busNr of that found bus - 2, which provides one bus number for the pci-expander-bus and one for the pci-bridge that is automatically attached to it (if you plan on adding more pci-bridges to the hierarchy of the bus, you should manually set busNr to a lower value).A similar algorithm is used for automatically determining the busNr attribute for pcie-expander-bus, but since the pcie-expander-bus doesn't have any built-in pci-bridge, the 2nd bus-number is just being reserved for the pcie-root-port that must necessarily be connected to the bus in order to actually plug in an endpoint device. If you intend to plug multiple devices into a pcie-expander-bus, you must connect a pcie-switch-upstream-port to the pcie-root-port that is plugged into the pcie-expander-bus, and multiple pcie-switch-downstream-ports to the pcie-switch-upstream-port, and of course for this to work properly, you will need to decrease the pcie-expander-bus' busNr accordingly so that there are enough unused bus numbers above it to accommodate giving out one bus number for the upstream-port and one for each downstream-port (in addition to the pcie-root-port and the pcie-expander-bus itself).
node
Some PCI controllers (
pci-expander-bus
for the pc machine type,pcie-expander-bus
for the q35 machine type and, since 3.6.0 ,pci-root
for the pseries machine type) can have an optional<node>
subelement within the<target>
subelement, which is used to set the NUMA node reported to the guest OS for that bus - the guest OS will then know that all devices on that bus are a part of the specified NUMA node (it is up to the user of the libvirt API to attach host devices to the correct pci-expander-bus when assigning them to the domain).index
pci-root controllers for pSeries guests use this attribute to record the order they will show up in the guest. Since 3.6.0
For machine types which provide an implicit PCI bus, the pci-root controller with index=0 is auto-added and required to use PCI devices. pci-root has no address. PCI bridges are auto-added if there are too many devices to fit on the one bus provided by pci-root, or a PCI bus number greater than zero was specified. PCI bridges can also be specified manually, but their addresses should only refer to PCI buses provided by already specified PCI controllers. Leaving gaps in the PCI controller indexes might lead to an invalid configuration.
...
<devices>
<controller type='pci' index='0' model='pci-root'/>
<controller type='pci' index='1' model='pci-bridge'>
<address type='pci' domain='0' bus='0' slot='5' function='0' multifunction='off'/>
</controller>
</devices>
...
For machine types which provide an implicit PCI Express (PCIe) bus (for example, the machine types based on the Q35 chipset), the pcie-root controller with index=0 is auto-added to the domain's configuration. pcie-root has also no address, provides 31 slots (numbered 1-31) that can be used to attach PCIe or PCI devices (although libvirt will never auto-assign a PCI device to a PCIe slot, it will allow manual specification of such an assignment). Devices connected to pcie-root cannot be hotplugged. If traditional PCI devices are present in the guest configuration, a pcie-to-pci-bridge
controller will automatically be added: this controller, which plugs into a pcie-root-port
, provides 31 usable PCI slots (1-31) with hotplug support ( since 4.3.0 ). If the QEMU binary doesn't support the corresponding device, then a dmi-to-pci-bridge
controller will be added instead, usually at the defacto standard location of slot=0x1e. A dmi-to-pci-bridge controller plugs into a PCIe slot (as provided by pcie-root), and itself provides 31 standard PCI slots (which also do not support device hotplug). In order to have hot-pluggable PCI slots in the guest system, a pci-bridge controller will also be automatically created and connected to one of the slots of the auto-created dmi-to-pci-bridge controller; all guest PCI devices with addresses that are auto-determined by libvirt will be placed on this pci-bridge device. ( since 1.1.2 ).
Domains with an implicit pcie-root can also add controllers with model='pcie-root-port'
, model='pcie-switch-upstream-port'
, and model='pcie-switch-downstream-port'
. pcie-root-port is a simple type of bridge device that can connect only to one of the 31 slots on the pcie-root bus on its upstream side, and makes a single (PCIe, hotpluggable) port available on the downstream side (at slot='0'). pcie-root-port can be used to provide a single slot to later hotplug a PCIe device (but is not itself hotpluggable - it must be in the configuration when the domain is started). ( since 1.2.19 )
pcie-switch-upstream-port is a more flexible (but also more complex) device that can only plug into a pcie-root-port or pcie-switch-downstream-port on the upstream side (and only before the domain is started - it is not hot-pluggable), and provides 32 ports on the downstream side (slot='0' - slot='31') that accept only pcie-switch-downstream-port devices; each pcie-switch-downstream-port device can only plug into a pcie-switch-upstream-port on its upstream side (again, not hot-pluggable), and on its downstream side provides a single hotpluggable pcie port that can accept any standard pci or pcie device (or another pcie-switch-upstream-port), i.e. identical in function to a pcie-root-port. ( since 1.2.19 )
...
<devices>
<controller type='pci' index='0' model='pcie-root'/>
<controller type='pci' index='1' model='pcie-root-port'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
</controller>
<controller type='pci' index='2' model='pcie-to-pci-bridge'>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</controller>
</devices>
...
Device leases
When using a lock manager, it may be desirable to record device leases against a VM. The lock manager will ensure the VM won't start unless the leases can be acquired.
...
<devices>
...
<lease>
<lockspace>somearea</lockspace>
<key>somekey</key>
<target path='/some/lease/path' offset='1024'/>
</lease>
...
</devices>
...
lockspace
This is an arbitrary string, identifying the lockspace within which the key is held. Lock managers may impose extra restrictions on the format, or length of the lockspace name.
key
This is an arbitrary string, uniquely identifying the lease to be acquired. Lock managers may impose extra restrictions on the format, or length of the key.
target
This is the fully qualified path of the file associated with the lockspace. The offset specifies where the lease is stored within the file. If the lock manager does not require an offset, just pass 0.
Host device assignment
USB / PCI / SCSI devices
USB, PCI and SCSI devices attached to the host can be passed through to the guest using the hostdev
element. since after 0.4.4 for USB, 0.6.0 for PCI (KVM only) and 1.0.6 for SCSI (KVM only) :
...
<devices>
<hostdev mode='subsystem' type='usb'>
<source startupPolicy='optional'>
<vendor id='0x1234'/>
<product id='0xbeef'/>
</source>
<boot order='2'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='pci' managed='yes'>
<source writeFiltering='no'>
<address domain='0x0000' bus='0x06' slot='0x02' function='0x0'/>
</source>
<boot order='1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi' sgio='filtered' rawio='yes'>
<source>
<adapter name='scsi_host0'/>
<address bus='0' target='0' unit='0'/>
</source>
<readonly/>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi'>
<source protocol='iscsi' name='iqn.2014-08.com.example:iscsi-nopool/1'>
<host name='example.com' port='3260'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
<initiator>
<iqn name='iqn.2020-07.com.example:test'/>
</initiator>
</source>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='scsi_host'>
<source protocol='vhost' wwpn='naa.50014057667280d8'/>
</hostdev>
</devices>
...
or:
...
<devices>
<hostdev mode='subsystem' type='mdev' model='vfio-pci'>
<source>
<address uuid='c2177883-f1bb-47f0-914d-32a22e3a8804'/>
</source>
</hostdev>
<hostdev mode='subsystem' type='mdev' model='vfio-ccw'>
<source>
<address uuid='9063cba3-ecef-47b6-abcf-3fef4fdcad85'/>
</source>
<address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0001'/>
</hostdev>
</devices>
...
hostdev
The
hostdev
element is the main container for describing host devices. For each device, themode
is always "subsystem" and thetype
is one of the following values with additional attributes noted.usb
USB devices are detached from the host on guest startup and reattached after the guest exits or the device is hot-unplugged.
pci
For PCI devices, when
managed
is "yes" it is detached from the host before being passed on to the guest and reattached to the host after the guest exits. Ifmanaged
is omitted or "no", the user is responsible to callvirNodeDeviceDetachFlags
(orvirsh nodedev-detach
before starting the guest or hot-plugging the device andvirNodeDeviceReAttach
(orvirsh nodedev-reattach
) after hot-unplug or stopping the guest.scsi
For SCSI devices, user is responsible to make sure the device is not used by host. If supported by the hypervisor and OS, the optional
sgio
( since 1.0.6 ) attribute indicates whether unprivileged SG_IO commands are filtered for the disk. Valid settings are "filtered" or "unfiltered", where the default is "filtered". The optionalrawio
( since 1.2.9 ) attribute indicates whether the lun needs the rawio capability. Valid settings are "yes" or "no". See the rawio description within the Hard drives, floppy disks, CDROMs section. If a disk lun in the domain already has the rawio capability, then this setting not required.scsi_host
since 2.5.0 For SCSI devices, user is responsible to make sure the device is not used by host. This
type
passes all LUNs presented by a single HBA to the guest. Since 5.2.0, themodel
attribute can be specified further with "virtio-transitional", "virtio-non-transitional", or "virtio". Virtio transitional devices for more details.mdev
For mediated devices ( Since 3.2.0 ) the
model
attribute specifies the device API which determines how the host's vfio driver will expose the device to the guest. Currently,model='vfio-pci'
,model='vfio-ccw'
( Since 4.4.0 ) andmodel='vfio-ap'
( Since 4.9.0 ) is supported. MDEV section provides more information about mediated devices as well as how to create mediated devices on the host. Since 4.6.0 (QEMU 2.12) an optionaldisplay
attribute may be used to enable or disable support for an accelerated remote desktop backed by a mediated device (such as NVIDIA vGPU or Intel GVT-g) as an alternative to emulated Video devices. This attribute is limited tomodel='vfio-pci'
only. Supported values are eitheron
oroff
(default is 'off'). It is required to use a graphical framebuffer (See Graphical framebuffers) in order to use this attribute, currently only supported with VNC, Spice and egl-headless graphics devices. Since version 5.10.0 , there is an optionalramfb
attribute for devices withmodel='vfio-pci'
. Supported values are eitheron
oroff
(default is 'off'). When enabled, this attribute provides a memory framebuffer device to the guest. This framebuffer will be used as a boot display when a vgpu device is the primary display.Note: There are also some implications on the usage of guest's address type depending on the
model
attribute, see theaddress
element below.
Note: The
managed
attribute is only used withtype='pci'
and is ignored by all the other device types, thus settingmanaged
explicitly with other than a PCI device has the same effect as omitting it. Similarly,model
attribute is only supported by mediated devices and ignored by all other device types.source
The source element describes the device as seen from the host using the following mechanism to describe:
usb
The USB device can either be addressed by vendor / product id using the
vendor
andproduct
elements or by the device's address on the host using theaddress
element.Since 1.0.0 , the
source
element of USB devices may containstartupPolicy
attribute which can be used to define policy what to do if the specified host USB device is not found. The attribute accepts the following values:mandatory fail if missing for any reason (the default) requisite fail if missing on boot up, drop if missing on migrate/restore/revert optional drop if missing at any start attempt pci
PCI devices can only be described by their
address
. Since 6.8.0 (Xen only) , thesource
element of a PCI device may contain thewriteFiltering
attribute to control write access to the PCI configuration space. By default Xen only allows writes of known safe values to the configuration space. SettingwriteFiltering='no'
will allow all writes to the device's PCI configuration space.scsi
SCSI devices are described by both the
adapter
andaddress
elements. Theaddress
element includes abus
attribute (a 2-digit bus number), atarget
attribute (a 10-digit target number), and aunit
attribute (a 20-digit unit number on the bus). Not all hypervisors support largertarget
andunit
values. It is up to each hypervisor to determine the maximum value supported for the adapter.Since 1.2.8 , the
source
element of a SCSI device may contain theprotocol
attribute. When the attribute is set to "iscsi", the host device XML follows the network disk device (See Hard drives, floppy disks, CDROMs) using the samename
attribute and optionally using theauth
element to provide the authentication credentials to the iSCSI server.Since 6.7.0, the optional
initiator
sub-element controls the IQN of the initiator ran by the hypervisor via it's<iqn name='iqn...'
subelement.scsi_host
Since 2.5.0 , multiple LUNs behind a single SCSI HBA are described by a
protocol
attribute set to "vhost" and awwpn
attribute that is the vhost_scsi wwpn (16 hexadecimal digits with a prefix of "naa.") established in the host configfs.mdev
Mediated devices ( Since 3.2.0 ) are described by the
address
element. Theaddress
element contains a single mandatory attributeuuid
.
vendor
,product
The
vendor
andproduct
elements each have anid
attribute that specifies the USB vendor and product id. The ids can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form.boot
Specifies that the device is bootable. The
order
attribute determines the order in which devices will be tried during boot sequence. The per-deviceboot
elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8 for PCI devices, Since 1.0.1 for USB devices.rom
The
rom
element is used to change how a PCI device's ROM is presented to the guest. The optionalbar
attribute can be set to "on" or "off", and determines whether or not the device's ROM will be visible in the guest's memory map. (In PCI documentation, the "rombar" setting controls the presence of the Base Address Register for the ROM). If no rom bar is specified, the qemu default will be used (older versions of qemu used a default of "off", while newer qemus have a default of "on"). Since 0.9.7 (QEMU and KVM only) . The optionalfile
attribute contains an absolute path to a binary file to be presented to the guest as the device's ROM BIOS. This can be useful, for example, to provide a PXE boot ROM for a virtual function of an sr-iov capable ethernet device (which has no boot ROMs for the VFs). Since 0.9.10 (QEMU and KVM only) . The optionalenabled
attribute can be set tono
to disable PCI ROM loading completely for the device; if PCI ROM loading is disabled through this attribute, attempts to tweak the loading process further using thebar
orfile
attributes will be rejected. Since 4.3.0 (QEMU and KVM only) .address
The
address
element for USB devices has abus
anddevice
attribute to specify the USB bus and device number the device appears at on the host. The values of these attributes can be given in decimal, hexadecimal (starting with 0x) or octal (starting with 0) form. For PCI devices the element carries 4 attributes allowing to designate the device as can be found with thelspci
or withvirsh nodedev-list
. For SCSI devices a 'drive' address type must be used. For mediated devices, which are software-only devices defining an allocation of resources on the physical parent device, the address type used must conform to themodel
attribute of elementhostdev
, e.g. any address type other than PCI forvfio-pci
device API or any address type other than CCW forvfio-ccw
device API will result in an error. See the Device Addresses section for more details on the address element.driver
PCI devices can have an optional
driver
subelement that specifies which backend driver to use for PCI device assignment. Use thename
attribute to select either "vfio" (for the new VFIO device assignment backend, which is compatible with UEFI SecureBoot) or "kvm" (the legacy device assignment handled directly by the KVM kernel module) Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer) . When specified, device assignment will fail if the requested method of device assignment isn't available on the host. When not specified, the default is "vfio" on systems where the VFIO driver is available and loaded, and "kvm" on older systems, or those where the VFIO driver hasn't been loaded Since 1.1.3 (prior to that the default was always "kvm").readonly
Indicates that the device is readonly, only supported by SCSI host device now. Since 1.0.6 (QEMU and KVM only)
shareable
If present, this indicates the device is expected to be shared between domains (assuming the hypervisor and OS support this). Only supported by SCSI host device. Since 1.0.6
Note: Although
shareable
was introduced in 1.0.6 , it did not work as as expected until 1.2.2 .
Block / character devices
Block / character devices from the host can be passed through to the guest using the hostdev
element. This is only possible with container based virtualization. Devices are specified by a fully qualified path. since after 1.0.1 for LXC :
...
<hostdev mode='capabilities' type='storage'>
<source>
<block>/dev/sdf1</block>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='misc'>
<source>
<char>/dev/input/event3</char>
</source>
</hostdev>
...
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
</hostdev>
...
hostdev
The
hostdev
element is the main container for describing host devices. For block/character device passthroughmode
is always "capabilities" andtype
is "storage" for a block device, "misc" for a character device and "net" for a host network interface.source
The source element describes the device as seen from the host. For block devices, the path to the block device in the host OS is provided in the nested "block" element, while for character devices the "char" element is used. For network interfaces, the name of the interface is provided in the "interface" element.
Redirected devices
USB device redirection through a character device is supported since after 0.9.5 (KVM only) :
...
<devices>
<redirdev bus='usb' type='spicevmc'/>
<redirdev bus='usb' type='tcp'>
<source mode='connect' host='localhost' service='4000'/>
<boot order='1'/>
</redirdev>
<redirfilter>
<usbdev class='0x08' vendor='0x1234' product='0xbeef' version='2.56' allow='yes'/>
<usbdev allow='no'/>
</redirfilter>
</devices>
...
redirdev
The
redirdev
element is the main container for describing redirected devices.bus
must be "usb" for a USB device. An additional attributetype
is required, matching one of the supported serial device types (See Consoles, serial, parallel & channel devices), to describe the host side of the tunnel;type='tcp'
ortype='spicevmc'
(which uses the usbredir channel of a SPICE graphics device (See Graphical framebuffers)) are typical.The redirdev element has an optional sub-element
<address>
which can tie the device to a particular controller. Further sub-elements, such as<source>
, may be required according to the given type, although a<target>
sub-element is not required (since the consumer of the character device is the hypervisor itself, rather than a device visible in the guest).boot
Specifies that the device is bootable. The
order
attribute determines the order in which devices will be tried during boot sequence. The per-deviceboot
elements cannot be used together with general boot elements in BIOS bootloader section. ( Since 1.0.1 )redirfilter
The
redirfilter
element is used for creating the filter rule to filter out certain devices from redirection. It uses sub-element<usbdev>
to define each filter rule.class
attribute is the USB Class code, for example, 0x08 represents mass storage devices. The USB device can be addressed by vendor / product id using thevendor
andproduct
attributes.version
is the device revision from the bcdDevice field (not the version of the USB protocol). These four attributes are optional and-1
can be used to allow any value for them.allow
attribute is mandatory, 'yes' means allow, 'no' for deny.
Smartcard devices
A virtual smartcard device can be supplied to the guest via the smartcard
element. A USB smartcard reader device on the host cannot be used on a guest with simple device passthrough, since it will then not be available on the host, possibly locking the host computer when it is "removed". Therefore, some hypervisors provide a specialized virtual device that can present a smartcard interface to the guest, with several modes for describing how credentials are obtained from the host or even a from a channel created to a third-party smartcard provider. Since 0.8.8
...
<devices>
<smartcard mode='host'/>
<smartcard mode='host-certificates'>
<certificate>cert1</certificate>
<certificate>cert2</certificate>
<certificate>cert3</certificate>
<database>/etc/pki/nssdb/</database>
</smartcard>
<smartcard mode='passthrough' type='tcp'>
<source mode='bind' host='127.0.0.1' service='2001'/>
<protocol type='raw'/>
<address type='ccid' controller='0' slot='0'/>
</smartcard>
<smartcard mode='passthrough' type='spicevmc'/>
</devices>
...
The <smartcard>
element has a mandatory attribute mode
. The following modes are supported; in each mode, the guest sees a device on its USB bus that behaves like a physical USB CCID (Chip/Smart Card Interface Device) card.
host
The simplest operation, where the hypervisor relays all requests from the guest into direct access to the host's smartcard via NSS. No other attributes or sub-elements are required. See below about the use of an optional
<address>
sub-element.host-certificates
Rather than requiring a smartcard to be plugged into the host, it is possible to provide three NSS certificate names residing in a database on the host. These certificates can be generated via the command
certutil -d /etc/pki/nssdb -x -t CT,CT,CT -S -s CN=cert1 -n cert1
, and the resulting three certificate names must be supplied as the content of each of three<certificate>
sub-elements. An additional sub-element<database>
can specify the absolute path to an alternate directory (matching the-d
option of thecertutil
command when creating the certificates); if not present, it defaults to /etc/pki/nssdb.passthrough
Rather than having the hypervisor directly communicate with the host, it is possible to tunnel all requests through a secondary character device to a third-party provider (which may in turn be talking to a smartcard or using three certificate files). In this mode of operation, an additional attribute
type
is required, matching one of the supported serial device types (See Consoles, serial, parallel & channel devices), to describe the host side of the tunnel;type='tcp'
ortype='spicevmc'
(which uses the smartcard channel of a SPICE graphics device (See Graphical framebuffers)) are typical. Further sub-elements, such as<source>
, may be required according to the given type, although a<target>
sub-element is not required (since the consumer of the character device is the hypervisor itself, rather than a device visible in the guest).
Each mode supports an optional sub-element <address>
(See Device Addresses), which fine-tunes the correlation between the smartcard and a ccid bus controller. For now, qemu only supports at most one smartcard, with an address of bus=0 slot=0.
Network interfaces
...
<devices>
<interface type='direct' trustGuestRxFilters='yes'>
<source dev='eth0'/>
<mac address='52:54:00:5d:c7:9e'/>
<boot order='1'/>
<rom bar='off'/>
<acpi index='4'/>
</interface>
</devices>
...
There are several possibilities for specifying a network interface visible to the guest. Each subsection below provides more details about common setup options.
Since 1.2.10 ), the interface
element property trustGuestRxFilters
provides the capability for the host to detect and trust reports from the guest regarding changes to the interface mac address and receive filters by setting the attribute to yes
. The default setting for the attribute is no
for security reasons and support depends on the guest network device model as well as the type of connection on the host - currently it is only supported for the virtio device model and for macvtap connections on the host.
Each <interface>
element has an optional <address>
sub-element that can tie the interface to a particular pci slot, with attribute type='pci'
as documented in the Device Addresses section.
Since 6.6.0 , one can force libvirt to keep the provided MAC address when it's in the reserved VMware range by adding a type="static"
attribute to the <mac/>
element. Note that this attribute is useless if the provided MAC address is outside of the reserved VMWare ranges.
Since 7.3.0, one can set the ACPI index against network interfaces. With some operating systems (eg Linux with systemd), the ACPI index is used to provide network interface device naming, that is stable across changes in PCI addresses assigned to the device. This value is required to be unique across all devices and be between 1 and (16*1024-1).
Virtual network
This is the recommended config for general guest connectivity on hosts with dynamic / wireless networking configs. (or multi-host environments where the host hardware details are described separately in a <network>
definition Since 0.9.4 ).
Provides a connection whose details are described by the named network definition. Depending on the virtual network's "forward mode" configuration, the network may be totally isolated (no <forward>
element given), NAT'ing to an explicit network device or to the default route (<forward mode='nat'>
), routed with no NAT (<forward mode='route'/>
), or connected directly to one of the host's network interfaces (via macvtap) or bridge devices ((<forward mode='bridge|private|vepa|passthrough'/>
Since 0.9.4 )
For networks with a forward mode of bridge, private, vepa, and passthrough, it is assumed that the host has any necessary DNS and DHCP services already setup outside the scope of libvirt. In the case of isolated, nat, and routed networks, DHCP and DNS are provided on the virtual network by libvirt, and the IP range can be determined by examining the virtual network config with 'virsh net-dumpxml [networkname]
'. There is one virtual network called 'default' setup out of the box which does NAT'ing to the default route and has an IP range of 192.168.122.0/255.255.255.0
. Each guest will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see Overriding the target element).
When the source of an interface is a network, a portgroup
can be specified along with the name of the network; one network may have multiple portgroups defined, with each portgroup containing slightly different configuration information for different classes of network connections. Since 0.9.4 .
When a guest is running an interface of type network
may include a portid
attribute. This provides the UUID of an associated virNetworkPortPtr object that records the association between the domain interface and the network. This attribute is read-only since port objects are create and deleted automatically during startup and shutdown. Since 5.1.0
Also, similar to direct
network connections (described below), a connection of type network
may specify a virtualport
element, with configuration data to be forwarded to a vepa (802.1Qbg) or 802.1Qbh compliant switch ( Since 0.8.2 ), or to an Open vSwitch virtual switch ( Since 0.9.11 ).
Since the actual type of switch may vary depending on the configuration in the <network>
on the host, it is acceptable to omit the virtualport type
attribute, and specify attributes from multiple different virtualport types (and also to leave out certain attributes); at domain startup time, a complete <virtualport>
element will be constructed by merging together the type and attributes defined in the network and the portgroup referenced by the interface. The newly-constructed virtualport is a combination of them. The attributes from lower virtualport can't make change on the ones defined in higher virtualport. Interface takes the highest priority, portgroup is lowest priority. ( Since 0.10.0 ). For example, in order to work properly with both an 802.1Qbh switch and an Open vSwitch switch, you may choose to specify no type, but both a profileid
(in case the switch is 802.1Qbh) and an interfaceid
(in case the switch is Open vSwitch) (you may also omit the other attributes, such as managerid, typeid, or profileid, to be filled in from the network's <virtualport>
). If you want to limit a guest to connecting only to certain types of switches, you can specify the virtualport type, but still omit some/all of the parameters - in this case if the host's network has a different type of virtualport, connection of the interface will fail.
...
<devices>
<interface type='network'>
<source network='default'/>
</interface>
...
<interface type='network'>
<source network='default' portgroup='engineering'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
<virtualport>
<parameters instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
</devices>
...
Bridge to LAN
This is the recommended config for general guest connectivity on hosts with static wired networking configs.
Provides a bridge from the VM directly to the LAN. This assumes there is a bridge device on the host which has one or more of the hosts physical NICs attached. The guest VM will have an associated tun device created with a name of vnetN, which can also be overridden with the <target> element (see Overriding the target element). The tun device will be attached to the bridge. The IP range / network configuration is whatever is used on the LAN. This provides the guest VM full incoming & outgoing net access just like a physical machine.
On Linux systems, the bridge device is normally a standard Linux host bridge. On hosts that support Open vSwitch, it is also possible to connect to an Open vSwitch bridge device by adding a <virtualport type='openvswitch'/>
to the interface definition. ( Since 0.9.11 ). The Open vSwitch type virtualport accepts two parameters in its <parameters>
element - an interfaceid
which is a standard uuid used to uniquely identify this particular interface to Open vSwitch (if you do not specify one, a random interfaceid will be generated for you when you first define the interface), and an optional profileid
which is sent to Open vSwitch as the interfaces "port-profile".
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='ovsbr'/>
<virtualport type='openvswitch'>
<parameters profileid='menial' interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
...
</devices>
...
On hosts that support Open vSwitch on the kernel side and have the Midonet Host Agent configured, it is also possible to connect to the 'midonet' bridge device by adding a <virtualport type='midonet'/>
to the interface definition. ( Since 1.2.13 ). The Midonet virtualport type requires an interfaceid
attribute in its <parameters>
element. This interface id is the UUID that specifies which port in the virtual network topology will be bound to the interface.
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
</interface>
<interface type='bridge'>
<source bridge='br1'/>
<target dev='vnet7'/>
<mac address="00:11:22:33:44:55"/>
</interface>
<interface type='bridge'>
<source bridge='midonet'/>
<virtualport type='midonet'>
<parameters interfaceid='0b2d64da-3d0e-431e-afdd-804415d6ebbb'/>
</virtualport>
</interface>
...
</devices>
...
Userspace SLIRP stack
Provides a virtual LAN with NAT to the outside world. The virtual network has DHCP & DNS services and will give the guest VM addresses starting from 10.0.2.15
. The default router will be 10.0.2.2
and the DNS server will be 10.0.2.3
. This networking is the only option for unprivileged users who need their VMs to have outgoing access. Since 3.8.0 it is possible to override the default network address by including an ip
element specifying an IPv4 address in its one mandatory attribute, address
. Optionally, a second ip
element with a family
attribute set to "ipv6" can be specified to add an IPv6 address to the interface. address
. Optionally, address prefix
can be specified.
...
<devices>
<interface type='user'/>
...
<interface type='user'>
<mac address="00:11:22:33:44:55"/>
<ip family='ipv4' address='172.17.2.0' prefix='24'/>
<ip family='ipv6' address='2001:db8:ac10:fd01::' prefix='64'/>
</interface>
</devices>
...
Generic ethernet connection
Provides a means to use a new or existing tap device (or veth device pair, depending on the needs of the hypervisor driver) that is partially or wholly setup external to libvirt (either prior to the guest starting, or while the guest is being started via an optional script specified in the config).
The name of the tap device can optionally be specified with the dev
attribute of the <target>
element. If no target dev is specified, libvirt will create a new standard tap device with a name of the pattern "vnetN", where "N" is replaced with a number. If a target dev is specified and that device doesn't exist, then a new standard tap device will be created with the exact dev name given. If the specified target dev does exist, then that existing device will be used. Usually some basic setup of the device is done by libvirt, including setting a MAC address, and the IFF_UP flag, but if the dev
is a pre-existing device, and the managed
attribute of the target
element is also set to "no" (the default value is "yes"), even this basic setup will not be performed - libvirt will simply pass the device on to the hypervisor with no setup at all. Since 5.7.0 Using managed='no' with a pre-created tap device is useful because it permits a virtual machine managed by an unprivileged libvirtd to have emulated network devices based on tap devices.
After creating/opening the tap device, an optional shell script (given in the path
attribute of the <script>
element) will be run. Since 0.2.1 Also, after detaching/closing the tap device, an optional shell script (given in the path
attribute of the <downscript>
element) will be run. Since 6.4.0 These can be used to do whatever extra host network integration is required.
...
<devices>
<interface type='ethernet'>
<script path='/etc/qemu-ifup-mynet'/>
<downscript path='/etc/qemu-ifdown-mynet'/>
</interface>
...
<interface type='ethernet'>
<target dev='mytap1' managed='no'/>
<model type='virtio'/>
</interface>
</devices>
...
Direct attachment to physical interface
This setup requires the Linux macvtap driver to be available. (Since Linux 2.6.34.) One of the modes 'vepa' ( 'Virtual Ethernet Port Aggregator'), 'bridge' or 'private' can be chosen for the operation mode of the macvtap device, 'vepa' being the default mode. The individual modes cause the delivery of packets to behave as follows:
If the model type is set to virtio
and interface's trustGuestRxFilters
attribute is set to yes
, changes made to the interface mac address, unicast/multicast receive filters, and vlan settings in the guest will be monitored and propagated to the associated macvtap device on the host ( Since 1.2.10 ). If trustGuestRxFilters
is not set, or is not supported for the device model in use, an attempted change to the mac address originating from the guest side will result in a non-working network connection.
vepa
All VMs' packets are sent to the external bridge. Packets whose destination is a VM on the same host as where the packet originates from are sent back to the host by the VEPA capable bridge (today's bridges are typically not VEPA capable).
bridge
Packets whose destination is on the same host as where they originate from are directly delivered to the target macvtap device. Both origin and destination devices need to be in bridge mode for direct delivery. If either one of them is in
vepa
mode, a VEPA capable bridge is required.private
All packets are sent to the external bridge and will only be delivered to a target VM on the same host if they are sent through an external router or gateway and that device sends them back to the host. This procedure is followed if either the source or destination device is in
private
mode.passthrough
This feature attaches a virtual function of a SRIOV capable NIC directly to a VM without losing the migration capability. All packets are sent to the VF/IF of the configured network device. Depending on the capabilities of the device additional prerequisites or limitations may apply; for example, on Linux this requires kernel 2.6.38 or newer. Since 0.9.2
...
<devices>
...
<interface type='direct' trustGuestRxFilters='no'>
<source dev='eth0' mode='vepa'/>
</interface>
</devices>
...
The network access of direct attached virtual machines can be managed by the hardware switch to which the physical interface of the host machine is connected to.
The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine. Since 0.8.2
Please note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID.
managerid
The VSI Manager ID identifies the database containing the VSI type and instance definitions. This is an integer value and the value 0 is reserved.
typeid
The VSI Type ID identifies a VSI type characterizing the network access. VSI types are typically managed by network administrator. This is an integer value.
typeidversion
The VSI Type Version allows multiple versions of a VSI Type. This is an integer value.
instanceid
The VSI Instance ID Identifier is generated when a VSI instance (i.e. a virtual interface of a virtual machine) is created. This is a globally unique identifier.
...
<devices>
...
<interface type='direct'>
<source dev='eth0.2' mode='vepa'/>
<virtualport type="802.1Qbg">
<parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
</virtualport>
</interface>
</devices>
...
The interface can have additional parameters as shown below if the switch is conforming to the IEEE 802.1Qbh standard. The values are network specific and should be provided by the network administrator. Since 0.8.2
profileid
The profile ID contains the name of the port profile that is to be applied to this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface.
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='private'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
PCI Passthrough
A PCI network device (specified by the <source> element) is directly assigned to the guest using generic device passthrough, after first optionally setting the device's MAC address to the configured value, and associating the device with an 802.1Qbh capable switch using an optionally specified <virtualport> element (see the examples of virtualport given above for type='direct' network devices). Note that - due to limitations in standard single-port PCI ethernet card driver design - only SR-IOV (Single Root I/O Virtualization) virtual function (VF) devices can be assigned in this manner; to assign a standard single-port PCI or PCIe ethernet card to a guest, use the traditional <hostdev> device definition and Since 0.9.11
To use VFIO device assignment rather than traditional/legacy KVM device assignment (VFIO is a new method of device assignment that is compatible with UEFI Secure Boot), a type='hostdev' interface can have an optional driver
sub-element with a name
attribute set to "vfio". To use legacy KVM device assignment you can set name
to "kvm" (or simply omit the <driver>
element, since "kvm" is currently the default). Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer)
Note that this "intelligent passthrough" of network devices is very similar to the functionality of a standard <hostdev> device, the difference being that this method allows specifying a MAC address and <virtualport> for the passed-through device. If these capabilities are not required, if you have a standard single-port PCI, PCIe, or USB network card that doesn't support SR-IOV (and hence would anyway lose the configured MAC address during reset after being assigned to the guest domain), or if you are using a version of libvirt older than 0.9.11, you should use standard <hostdev> to assign the device to the guest instead of <interface type='hostdev'/>.
Similar to the functionality of a standard <hostdev> device, when managed
is "yes", it is detached from the host before being passed on to the guest, and reattached to the host after the guest exits. If managed
is omitted or "no", the user is responsible to call virNodeDeviceDettach
(or virsh nodedev-detach
) before starting the guest or hot-plugging the device, and virNodeDeviceReAttach
(or virsh nodedev-reattach
) after hot-unplug or stopping the guest.
...
<devices>
<interface type='hostdev' managed='yes'>
<driver name='vfio'/>
<source>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</source>
<mac address='52:54:00:6d:90:02'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
vDPA devices
A vDPA network device can be used to provide wire speed network performance within a domain. A vDPA device is a specialized type of network device that uses a datapath that complies with the virtio specification but has a vendor-specific control path. To use such a device with libvirt, the host device must already be bound to the appropriate device-specific vDPA driver. This creates a vDPA char device (e.g. /dev/vhost-vdpa-0) that can be used to assign the device to a libvirt domain. Since 6.9.0 (QEMU only, requires QEMU 5.1.0 or newer)
...
<devices>
<interface type='vdpa'>
<source dev='/dev/vhost-vdpa-0'/>
</interface>
</devices>
...
Teaming a virtio/hostdev NIC pair
Since 6.1.0 (QEMU and KVM only, requires QEMU 4.2.0 or newer and a guest virtio-net driver supporting the "failover" feature, such as the one included in Linux kernel 4.18 and newer) The <teaming>
element of two interfaces can be used to connect them as a team/bond device in the guest (assuming proper support in the hypervisor and the guest network driver).
...
<devices>
<interface type='network'>
<source network='mybridge'/>
<mac address='00:11:22:33:44:55'/>
<model type='virtio'/>
<teaming type='persistent'/>
<alias name='ua-backup0'/>
</interface>
<interface type='network'>
<source network='hostdev-pool'/>
<mac address='00:11:22:33:44:55'/>
<model type='virtio'/>
<teaming type='transient' persistent='ua-backup0'/>
</interface>
</devices>
...
The second interface in this example is referencing a network that is a pool of SRIOV VFs (i.e. a "hostdev network"). You could instead directly reference an SRIOV VF device:
...
<interface type='hostdev'>
<source>
<address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</source>
<mac address='00:11:22:33:44:55:66'/>
<teaming type='transient' persistent='ua-backup0'/>
</interface>
...
The <teaming>
element required attribute type
will be set to either "persistent"
to indicate a device that should always be present in the domain, or "transient"
to indicate a device that may periodically be removed, then later re-added to the domain. When type="transient", there should be a second attribute to <teaming>
called "persistent"
- this attribute should be set to the alias name of the other device in the pair (the one that has <teaming type="persistent'/>
).
In the particular case of QEMU, libvirt's <teaming>
element is used to setup a virtio-net "failover" device pair. For this setup, the persistent device must be an interface with <model type="virtio"/>
, and the transient device must be <interface type='hostdev'/>
(or <interface type='network'/>
where the referenced network defines a pool of SRIOV VFs). The guest will then have a simple network team/bond device made of the virtio NIC + hostdev NIC pair. In this configuration, the higher-performing hostdev NIC will normally be preferred for all network traffic, but when the domain is migrated, QEMU will automatically unplug the VF from the guest, and then hotplug a similar device once migration is completed; while migration is taking place, network traffic will use the virtio NIC. (Of course the emulated virtio NIC and the hostdev NIC must be connected to the same subnet for bonding to work properly).
Since 7.1.0 The <teaming>
element can also be added to a plain <hostdev>
device.
...
<hostdev mode='subsystem' type='pci' managed='no'>
<source>
<address domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</source>
<teaming type='transient' persistent='ua-backup0'/>
</hostdev>
...
This device must be a network device, but not necessarily an SRIOV VF. Using plain <hostdev>
rather than <interface type='hostdev'>
or <interface type='network'>
is useful if the device that will be assigned with VFIO is a standard NIC (not a VF) or if libvirt doesn't have the necessary resources and privileges to set the VF's MAC address (e.g. if libvirt is running unprivileged, or in a container). This of course means that the user (or another application) is responsible for setting the MAC address of the device in a way such that it will survive guest driver initialization. For standard NICs (i.e. not an SRIOV VF) this probably means that the NIC's factory-programmed MAC address will need to be used for the teaming pair (since any driver init in the guest will reset the MAC back to factory). If it is an SRIOV VF, then its MAC address will need to be set via the VF's PF, e.g. if you are going to use VF 2 of the PF enp2s0f1, you would use something like this command:
ip link set enp2s0f1 vf 2 mac 52:54:00:11:22:33
NB1: Since you must know the alias name of the virtio NIC when configuring the hostdev NIC, it will need to be manually set in the virtio NIC's configuration (as with all other manually set alias names, this means it must start with "ua-").
NB2: Currently the only implementation of the guest OS virtio-net driver supporting virtio-net failover requires that the MAC addresses of the virtio and hostdev NIC must match. Since that may not always be a requirement in the future, libvirt doesn't enforce this limitation - it is up to the person/management application that is creating the configuration to assure the MAC addresses of the two devices match.
NB3: Since the PCI addresses of the SRIOV VFs on the hosts that are the source and destination of the migration will almost certainly be different, either higher level management software will need to modify the <source>
of the hostdev NIC (<interface type='hostdev'>
) at the start of migration, or (a simpler solution) the configuration will need to use a libvirt "hostdev" virtual network that maintains a pool of such devices, as is implied in the example's use of the libvirt network named "hostdev-pool" - as long as the hostdev network pools on both hosts have the same name, libvirt itself will take care of allocating an appropriate device on both ends of the migration. Similarly the XML for the virtio interface must also either work correctly unmodified on both the source and destination of the migration (e.g. by connecting to the same bridge device on both hosts, or by using the same virtual network), or the management software must properly modify the interface XML during migration so that the virtio device remains connected to the same network segment before and after migration.
Multicast tunnel
A multicast group is setup to represent a virtual network. Any VMs whose network devices are in the same multicast group can talk to each other even across hosts. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing. The multicast protocol is compatible with that used by user mode linux guests too. The source address used must be from the multicast address block.
...
<devices>
<interface type='mcast'>
<mac address='52:54:00:6d:90:01'/>
<source address='230.0.0.1' port='5558'/>
</interface>
</devices>
...
TCP tunnel
A TCP client/server architecture provides a virtual network. One VM provides the server end of the network, all other VMS are configured as clients. All network traffic is routed between the VMs via the server. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the VMs should have a 2nd NIC which is connected to one of the first 4 network types and do the appropriate routing.
...
<devices>
<interface type='server'>
<mac address='52:54:00:22:c9:42'/>
<source address='192.168.0.1' port='5558'/>
</interface>
...
<interface type='client'>
<mac address='52:54:00:8b:c9:51'/>
<source address='192.168.0.1' port='5558'/>
</interface>
</devices>
...
UDP unicast tunnel
A UDP unicast architecture provides a virtual network which enables connections between QEMU instances using QEMU's UDP infrastructure. The xml "source" address is the endpoint address to which the UDP socket packets will be sent from the host running QEMU. The xml "local" address is the address of the interface from which the UDP socket packets will originate from the QEMU host. Since 1.2.20
...
<devices>
<interface type='udp'>
<mac address='52:54:00:22:c9:42'/>
<source address='127.0.0.1' port='11115'>
<local address='127.0.0.1' port='11116'/>
</source>
</interface>
</devices>
...
Setting the NIC model
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='ne2k_pci'/>
</interface>
</devices>
...
For hypervisors which support this, you can set the model of emulated network interface card.
The values for type
aren't defined specifically by libvirt, but by what the underlying hypervisor supports (if any). For QEMU and KVM you can get a list of supported models with these commands:
qemu -net nic,model=? /dev/null
qemu-kvm -net nic,model=? /dev/null
Typical values for QEMU and KVM include: ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio. Since 5.2.0 , virtio-transitional
and virtio-non-transitional
values are supported. See Virtio transitional devices for more details.
Setting NIC driver-specific options
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5' rx_queue_size='256' tx_queue_size='256'>
<host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/>
<guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
</driver>
</interface>
</devices>
...
Some NICs may have tunable driver-specific options. These are set as attributes of the driver
sub-element of the interface definition. Currently the following attributes are available for the "virtio"
NIC driver:
name
The optional
name
attribute forces which type of backend driver to use. The value can be either 'qemu' (a user-space backend) or 'vhost' (a kernel backend, which requires the vhost module to be provided by the kernel); an attempt to require the vhost driver without kernel support will be rejected. If this attribute is not present, then the domain defaults to 'vhost' if present, but silently falls back to 'qemu' without error. Since 0.8.8 (QEMU and KVM only) For interfaces of type='hostdev' (PCI passthrough devices) thename
attribute can optionally be set to "vfio" or "kvm". "vfio" tells libvirt to use VFIO device assignment rather than traditional KVM device assignment (VFIO is a new method of device assignment that is compatible with UEFI Secure Boot), and "kvm" tells libvirt to use the legacy device assignment performed directly by the kvm kernel module (the default is currently "kvm", but is subject to change). Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer) For interfaces of type='vhostuser', thename
attribute is ignored. The backend driver used is always vhost-user.txmode
The
txmode
attribute specifies how to handle transmission of packets when the transmit buffer is full. The value can be either 'iothread' or 'timer'. Since 0.8.8 (QEMU and KVM only) If set to 'iothread', packet tx is all done in an iothread in the bottom half of the driver (this option translates into adding "tx=bh" to the qemu commandline -device virtio-net-pci option). If set to 'timer', tx work is done in qemu, and if there is more tx data than can be sent at the present time, a timer is set before qemu moves on to do other things; when the timer fires, another attempt is made to send more data. The resulting difference, according to the qemu developer who added the option is: "bh makes tx more asynchronous and reduces latency, but potentially causes more processor bandwidth contention since the CPU doing the tx isn't necessarily the CPU where the guest generated the packets." In general you should leave this option alone, unless you are very certain you know what you are doing.ioeventfd
This optional attribute allows users to set domain I/O asynchronous handling for interface device. The default is left to the discretion of the hypervisor. Accepted values are "on" and "off". Enabling this allows qemu to execute VM while a separate thread handles I/O. Typically guests experiencing high system CPU utilization during I/O will benefit from this. On the other hand, on overloaded host it could increase guest I/O latency. Since 0.9.3 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.
event_idx
The
event_idx
attribute controls some aspects of device event processing. The value can be either 'on' or 'off' - if it is on, it will reduce the number of interrupts and exits for the guest. The default is determined by QEMU; usually if the feature is supported, default is on. In case there is a situation where this behavior is suboptimal, this attribute provides a way to force the feature off. Since 0.9.5 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.queues
The optional
queues
attribute controls the number of queues to be used for either Multiqueue virtio-net or vhost-user (See vhost-user interface) network interfaces. Use of multiple packet processing queues requires the interface having the<model type='virtio'/>
element. Each queue will potentially be handled by a different processor, resulting in much higher throughput. virtio-net since 1.0.6 (QEMU and KVM only) vhost-user since 1.2.17 (QEMU and KVM only)rx_queue_size
The optional
rx_queue_size
attribute controls the size of virtio ring for each queue as described above. The default value is hypervisor dependent and may change across its releases. Moreover, some hypervisors may pose some restrictions on actual value. For instance, latest QEMU (as of 2016-09-01) requires value to be a power of two from [256, 1024] range. Since 2.3.0 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.tx_queue_size
The optional
tx_queue_size
attribute controls the size of virtio ring for each queue as described above. The default value is hypervisor dependent and may change across its releases. Moreover, some hypervisors may pose some restrictions on actual value. For instance, QEMU v2.9 requires value to be a power of two from [256, 1024] range. In addition to that, this may work only for a subset of interface types, e.g. aforementioned QEMU enables this option only forvhostuser
type. Since 3.7.0 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing.rss
The
rss
option enables in-qemu/ebpf RSS for virtio NIC. RSS works with virtio and tap backends only. Virtio NIC will be launched with "rss" property. For now "in-qemu" RSS is supported by libvirt. QEMU may load eBPF RSS if it has CAP_SYS_ADMIN permissions, which is not supported by default in libvirt. Since 8.3.0 and QEMU 5.1 In general you should leave this option alone, unless you are very certain you know what you are doing. Proper RSS configuration depends from vcpu, tap, and vhost settings.rss_hash_report
The
rss_hash_report
option enables in-qemu RSS hash report for virtio NIC. Virtio NIC will be launched with a "hash" property. Network packets provided to VM will contain a hash of the packet in the virt header. Usually enabled alongside withrss
. Withoutrss
option, the hash report doesn't affect steering itself but provides vnet header with a calculated hash. Since 8.3.0 and QEMU 5.1 In general you should leave this option alone, unless you are very certain you know what you are doing. Proper RSS configuration depends from vcpu, tap, and vhost settings.- virtio options
For virtio interfaces, Virtio-related options can also be set. ( Since 3.5.0 )
Offloading options for the host and guest can be configured using the following sub-elements:
host
The
csum
,gso
,tso4
,tso6
,ecn
andufo
attributes with possible valueson
andoff
can be used to turn off host offloading options. By default, the supported offloads are enabled by QEMU. Since 1.2.9 (QEMU only) Themrg_rxbuf
attribute can be used to control mergeable rx buffers on the host side. Possible values areon
(default) andoff
. Since 1.2.13 (QEMU only)guest
The
csum
,tso4
,tso6
,ecn
andufo
attributes with possible valueson
andoff
can be used to turn off guest offloading options. By default, the supported offloads are enabled by QEMU. Since 1.2.9 (QEMU only)
Setting network backend-specific options
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<model type='virtio'/>
<backend tap='/dev/net/tun' vhost='/dev/vhost-net'/>
<driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/>
<tune>
<sndbuf>1600</sndbuf>
</tune>
</interface>
</devices>
...
For tuning the backend of the network, the backend
element can be used. The vhost
attribute can override the default vhost device path (/dev/vhost-net
) for devices with virtio
model. The tap
attribute overrides the tun/tap device path (default: /dev/net/tun
) for network and bridge interfaces. This does not work in session mode. Since 1.2.9
For tap devices there is also sndbuf
element which can adjust the size of send buffer in the host. Since 0.8.8
Overriding the target element
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
</interface>
</devices>
...
If no target is specified, certain hypervisors will automatically generate a name for the created tun device. This name can be manually specified, however the name should not start with either 'vnet', 'vif', 'macvtap', or 'macvlan', which are prefixes reserved by libvirt and certain hypervisors. Manually specified targets using these prefixes may be ignored.
Note that for LXC containers, this defines the name of the interface on the host side. Since 1.2.7 , to define the name of the device on the guest side, the guest
element should be used, as in the following snippet:
...
<devices>
<interface type='network'>
<source network='default'/>
<guest dev='myeth'/>
</interface>
</devices>
...
Specifying boot order
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<boot order='1'/>
</interface>
</devices>
...
For hypervisors which support this, you can set a specific NIC to be used for network boot. The order
attribute determines the order in which devices will be tried during boot sequence. The per-device boot
elements cannot be used together with general boot elements in BIOS bootloader section. Since 0.8.8
Interface ROM BIOS configuration
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet1'/>
<rom bar='on' file='/etc/fake/boot.bin'/>
</interface>
</devices>
...
For hypervisors which support this, you can change how a PCI Network device's ROM is presented to the guest. The bar
attribute can be set to "on" or "off", and determines whether or not the device's ROM will be visible in the guest's memory map. (In PCI documentation, the "rombar" setting controls the presence of the Base Address Register for the ROM). If no rom bar is specified, the qemu default will be used (older versions of qemu used a default of "off", while newer qemus have a default of "on"). The optional file
attribute is used to point to a binary file to be presented to the guest as the device's ROM BIOS. This can be useful to provide an alternative boot ROM for a network device. Since 0.9.10 (QEMU and KVM only) .
Setting up a network backend in a driver domain
...
<devices>
...
<interface type='bridge'>
<source bridge='br0'/>
<backenddomain name='netvm'/>
</interface>
...
</devices>
...
The optional backenddomain
element allows specifying a backend domain (aka driver domain) for the interface. Use the name
attribute to specify the backend domain name. You can use it to create a direct network link between domains (so data will not go through host system). Use with type 'ethernet' to create plain network link, or with type 'bridge' to connect to a bridge inside the backend domain. Since 1.2.13 (Xen only)
Quality of service
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<bandwidth>
<inbound average='1000' peak='5000' floor='200' burst='1024'/>
<outbound average='128' peak='256' burst='256'/>
</bandwidth>
</interface>
</devices>
...
This part of interface XML provides setting quality of service. Incoming and outgoing traffic can be shaped independently. The bandwidth
element and its child elements are described in the QoS section of the Network XML.
Setting VLAN tag (on supported network types only)
...
<devices>
<interface type='bridge'>
<vlan>
<tag id='42'/>
</vlan>
<source bridge='ovsbr0'/>
<virtualport type='openvswitch'>
<parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/>
</virtualport>
</interface>
<interface type='bridge'>
<vlan trunk='yes'>
<tag id='42'/>
<tag id='123' nativeMode='untagged'/>
</vlan>
...
</interface>
</devices>
...
If (and only if) the network connection used by the guest supports VLAN tagging transparent to the guest, an optional <vlan>
element can specify one or more VLAN tags to apply to the guest's network traffic Since 0.10.0 . Network connections that support guest-transparent VLAN tagging include 1) type='bridge' interfaces connected to an Open vSwitch bridge Since 0.10.0 , 2) SRIOV Virtual Functions (VF) used via type='hostdev' (direct device assignment) Since 0.10.0 , and 3) SRIOV VFs used via type='direct' with mode='passthrough' (macvtap "passthru" mode) Since 1.3.5 . All other connection types, including standard linux bridges and libvirt's own virtual networks, do not support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches provide their own way (outside of libvirt) to tag guest traffic onto a specific VLAN. Each tag is given in a separate <tag>
subelement of <vlan>
(for example: <tag id='42'/>
). For VLAN trunking of multiple tags (which is supported only on Open vSwitch connections), multiple <tag>
subelements can be specified, which implies that the user wants to do VLAN trunking on the interface for all the specified tags. In the case that VLAN trunking of a single tag is desired, the optional attribute trunk='yes'
can be added to the toplevel <vlan>
element to differentiate trunking of a single tag from normal tagging.
For network connections using Open vSwitch it is also possible to configure 'native-tagged' and 'native-untagged' VLAN modes Since 1.1.0. This is done with the optional nativeMode
attribute on the <tag>
subelement: nativeMode
may be set to 'tagged' or 'untagged'. The id
attribute of the <tag>
subelement containing nativeMode
sets which VLAN is considered to be the "native" VLAN for this interface, and the nativeMode
attribute determines whether or not traffic for that VLAN will be tagged.
Isolating guests's network traffic from each other
...
<devices>
<interface type='network'>
<source network='default'/>
<port isolated='yes'/>
</interface>
</devices>
...
Since 6.1.0. The port
element property isolated
, when set to yes
(default setting is no
) is used to isolate this interface's network traffic from that of other guest interfaces connected to the same network that also have <port isolated='yes'/>
. This setting is only supported for emulated interface devices that use a standard tap device to connect to the network via a Linux host bridge. This property can be inherited from a libvirt network, so if all guests that will be connected to the network should be isolated, it is better to put the setting in the network configuration. (NB: this only prevents guests that have isolated='yes'
from communicating with each other; if there is a guest on the same bridge that doesn't have isolated='yes'
, even the isolated guests will be able to communicate with it.)
Modifying virtual link state
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<link state='down'/>
</interface>
</devices>
...
This element provides means of setting state of the virtual network link. Possible values for attribute state
are up
and down
. If down
is specified as the value, the interface behaves as if it had the network cable disconnected. Default behavior if this element is unspecified is to have the link state up
. Since 0.9.5
MTU configuration
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<mtu size='1500'/>
</interface>
</devices>
...
This element provides means of setting MTU of the virtual network link. Currently there is just one attribute size
which accepts a non-negative integer which specifies the MTU size for the interface. Since 3.1.0
Coalesce settings
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<coalesce>
<rx>
<frames max='7'/>
</rx>
</coalesce>
</interface>
</devices>
...
This element provides means of setting coalesce settings for some interface devices (currently only type network
and bridge
. Currently there is just one attribute, max
, to tweak, in element frames
for the rx
group, which accepts a non-negative integer that specifies the maximum number of packets that will be received before an interrupt. Since 3.3.0
IP configuration
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<ip address='192.168.122.5' prefix='24'/>
<ip address='192.168.122.5' prefix='24' peer='10.0.0.10'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</interface>
...
<hostdev mode='capabilities' type='net'>
<source>
<interface>eth0</interface>
</source>
<ip address='192.168.122.6' prefix='24'/>
<route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/>
<route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/>
</hostdev>
...
</devices>
...
Since 1.2.12 network devices and hostdev devices with network capabilities can optionally be provided one or more IP addresses to set on the network device in the guest. Note that some hypervisors or network device types will simply ignore them or only use the first one. The family
attribute can be set to either ipv4
or ipv6
, and the address
attribute contains the IP address. The optional prefix
is the number of 1 bits in the netmask, and will be automatically set if not specified - for IPv4 the default prefix is determined according to the network "class" (A, B, or C - see RFC870), and for IPv6 the default prefix is 64. The optional peer
attribute holds the IP address of the other end of a point-to-point network device (since 2.1.0) .
Since 1.2.12 route elements can also be added to define IP routes to add in the guest. The attributes of this element are described in the documentation for the route
element in network definitions. This is used by the LXC driver.
...
<devices>
<interface type='ethernet'>
<source/>
<ip address='192.168.123.1' prefix='24'/>
<ip address='10.0.0.10' prefix='24' peer='192.168.122.5'/>
<route family='ipv4' address='192.168.42.0' prefix='24' gateway='192.168.123.4'/>
<source/>
...
</interface>
...
</devices>
...
Since 2.1.0 network devices of type "ethernet" can optionally be provided one or more IP addresses and one or more routes to set on the host side of the network device. These are configured as subelements of the <source>
element of the interface, and have the same attributes as the similarly named elements used to configure the guest side of the interface (described above).
vhost-user interface
Since 1.2.7 the vhost-user enables the communication between a QEMU virtual machine and other userspace process using the Virtio transport protocol. A char dev (e.g. Unix socket) is used for the control plane, while the data plane is based on shared memory.
...
<devices>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1a'/>
<source type='unix' path='/tmp/vhost1.sock' mode='server'/>
<model type='virtio'/>
</interface>
<interface type='vhostuser'>
<mac address='52:54:00:3b:83:1b'/>
<source type='unix' path='/tmp/vhost2.sock' mode='client'>
<reconnect enabled='yes' timeout='10'/>
</source>
<model type='virtio'/>
<driver queues='5'/>
</interface>
</devices>
...
The <source>
element has to be specified along with the type of char device. Currently, only type='unix' is supported, where the path (the directory path of the socket) and mode attributes are required. Both mode='server'
and mode='client'
are supported. vhost-user requires the virtio model type, thus the <model>
element is mandatory. Since 4.1.0 the element has an optional child element reconnect
which configures reconnect timeout if the connection is lost. It has two attributes enabled
(which accepts yes
and no
) and timeout
which specifies the amount of seconds after which hypervisor tries to reconnect.
Traffic filtering with NWFilter
Since 0.8.0 an nwfilter
profile can be assigned to a domain interface, which allows configuring traffic filter rules for the virtual machine. See the nwfilter documentation for more complete details.
...
<devices>
<interface ...>
...
<filterref filter='clean-traffic'/>
</interface>
<interface ...>
...
<filterref filter='myfilter'>
<parameter name='IP' value='104.207.129.11'/>
<parameter name='IP6_ADDR' value='2001:19f0:300:2102::'/>
<parameter name='IP6_MASK' value='64'/>
...
</filterref>
</interface>
</devices>
...
The filter
attribute specifies the name of the nwfilter to use. Optional <parameter>
elements may be specified for passing additional info to the nwfilter via the name
and value
attributes. See the nwfilter docs for info on parameters.
Input devices
Input devices allow interaction with the graphical framebuffer in the guest virtual machine. When enabling the framebuffer, an input device is automatically provided. It may be possible to add additional devices explicitly, for example, to provide a graphics tablet for absolute cursor movement.
...
<devices>
<input type='mouse' bus='usb'/>
<input type='keyboard' bus='usb'/>
<input type='mouse' bus='virtio'/>
<input type='keyboard' bus='virtio'/>
<input type='tablet' bus='virtio'/>
<input type='passthrough' bus='virtio'>
<source evdev='/dev/input/event1'/>
</input>
<input type='evdev'>
<source dev='/dev/input/event1234' grab='all' repeat='on' grabToggle='ctrl-ctrl'/>
</input>
</devices>
...
input
The
input
element has one mandatory attribute, thetype
whose value can be 'mouse', 'tablet', ( since 1.2.2 ) 'keyboard', ( since 1.3.0 ) 'passthrough' or ( since 7.4.0 ) 'evdev'. The tablet provides absolute cursor movement, while the mouse uses relative movement. The optionalbus
attribute can be used to refine the exact device type. It takes values "xen" (paravirtualized), "ps2" and "usb" or ( since 1.3.0 ) "virtio".
The input
element has an optional sub-element <address>
which can tie the device to a particular PCI slot, documented in the Device Addresses section. On S390, address
can be used to provide a CCW address for an input device ( since 4.2.0 ). For types passthrough
and evdev
, the mandatory sub-element source
must have an evdev
(for passthrough
) or dev
(for evdev
) attribute containing the absolute path to the event device passed through to guests. For type evdev
, source
has three optional attributes grab
with value 'all' which when enabled grabs all input devices instead of just one, repeat
with value 'on'/'off' to enable/disable auto-repeat events and grabToggle
(since 7.6.0) with values ctrl-ctrl
, alt-alt
, shift-shift
, meta-meta
, scrolllock
or ctrl-scrolllock
to change the grab key combination. input
type evdev
is currently supported only on linux devices. (KVM only) Since 5.2.0 , the input
element accepts a model
attribute which has the values 'virtio', 'virtio-transitional' and 'virtio-non-transitional'. See Virtio transitional devices for more details.
The subelement driver
can be used to tune the virtio options of the device: Virtio-related options can also be set. ( Since 3.5.0 )
Hub devices
A hub is a device that expands a single port into several so that there are more ports available to connect devices to a host system.
...
<devices>
<hub type='usb'/>
</devices>
...
hub
The
hub
element has one mandatory attribute, thetype
whose value can only be 'usb'.
The hub
element has an optional sub-element <address>
(See Device Addresses) type='usb'
which can tie the device to a particular controller.
Graphical framebuffers
A graphics device allows for graphical interaction with the guest OS. A guest will typically have either a framebuffer or a text console configured to allow interaction with the admin.
...
<devices>
<graphics type='sdl' display=':0.0'/>
<graphics type='vnc' port='5904' sharePolicy='allow-exclusive'>
<listen type='address' address='1.2.3.4'/>
</graphics>
<graphics type='rdp' autoport='yes' multiUser='yes' />
<graphics type='desktop' fullscreen='yes'/>
<graphics type='spice'>
<listen type='network' network='rednet'/>
</graphics>
</devices>
...
graphics
The
graphics
element has a mandatorytype
attribute which takes the valuesdl
,vnc
,spice
,rdp
,desktop
oregl-headless
:sdl
This displays a window on the host desktop, it can take 3 optional arguments: a
display
attribute for the display to use, anxauth
attribute for the authentication identifier, and an optionalfullscreen
attribute accepting valuesyes
orno
.You can use a
gl
with theenable="yes"
property to enable OpenGL support in SDL. Likewise you can explicitly disable OpenGL support withenable="no"
.vnc
Starts a VNC server. The
port
attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). Theautoport
attribute is the new preferred syntax for indicating auto-allocation of the TCP port to use. Thepasswd
attribute provides a VNC password in clear text. If thepasswd
attribute is set to an empty string, then VNC access is disabled. Thekeymap
attribute specifies the keymap to use. It is possible to set a limit on the validity of the password by giving a timestamppasswdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. Theconnected
attribute allows control of connected client during password changes. VNC acceptskeep
value only since 0.9.3 . NB, this may not be supported by all hypervisors.The optional
sharePolicy
attribute specifies vnc server display sharing policy.allow-exclusive
allows clients to ask for exclusive access by dropping other connections. Connecting multiple clients in parallel requires all clients asking for a shared session (vncviewer: -Shared switch). This is the default value.force-shared
disables exclusive client access, every connection has to specify -Shared switch for vncviewer.ignore
welcomes every connection unconditionally since 1.0.6 .Rather than using listen/port, QEMU supports a
socket
attribute for listening on a unix domain socket path Since 0.8.8 .For VNC WebSocket functionality,
websocket
attribute may be used to specify port to listen on (with -1 meaning auto-allocation andautoport
having no effect due to security reasons) Since 1.0.6 .For VNC, the
powerControl
attribute can be used to enable VM shutdown, reboot and reset power control features for the VNC client. This is appropriate if the authenticated VNC client user already has administrator privileges in the guest Since 7.1.0.Although VNC doesn't support OpenGL natively, it can be paired with graphics type
egl-headless
(see below) which will instruct QEMU to open and use drm nodes for OpenGL rendering.A VNC server could be optionally mapped to the specific host audio backend using the
<audio>
sub-element:<graphics type='vnc' ...> <audio id='1'> </graphics>
Where
1
is an id of the audio device (SeeAudio backends). If no ID is specified, then the default audio backend will be used. Since 7.2.0, qemu.spice
Since 0.8.6Starts a SPICE server. The
port
attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated), whiletlsPort
gives an alternative secure port number. Theautoport
attribute is the new preferred syntax for indicating auto-allocation of needed port numbers. Thepasswd
attribute provides a SPICE password in clear text. If thepasswd
attribute is set to an empty string, then SPICE access is disabled. Thekeymap
attribute specifies the keymap to use. It is possible to set a limit on the validity of the password by giving a timestamppasswdValidTo='2010-04-09T15:51:00'
assumed to be in UTC.The
connected
attribute allows control of connected client during password changes. SPICE acceptskeep
to keep client connected,disconnect
to disconnect client andfail
to fail changing password . NB, this may not be supported by all hypervisors. Since 0.9.3The
defaultMode
attribute sets the default channel security policy, valid values aresecure
,insecure
and the defaultany
(which is secure if possible, but falls back to insecure rather than erroring out if no secure path is available). Since 0.9.12When SPICE has both a normal and TLS secured TCP port configured, it can be desirable to restrict what channels can be run on each port. This is achieved by adding one or more
<channel>
elements inside the main<graphics>
element and setting themode
attribute to eithersecure
orinsecure
. Setting the mode attribute overrides the default value as set by thedefaultMode
attribute. (Note that specifyingany
as mode discards the entry as the channel would inherit the default mode anyways.) Valid channel names includemain
,display
,inputs
,cursor
,playback
,record
(all since 0.8.6 );smartcard
( since 0.8.8 ); andusbredir
( since 0.9.12 ).<graphics type='spice' port='-1' tlsPort='-1' autoport='yes'> <channel name='main' mode='secure'/> <channel name='record' mode='insecure'/> <image compression='auto_glz'/> <streaming mode='filter'/> <clipboard copypaste='no'/> <mouse mode='client'/> <filetransfer enable='no'/> <gl enable='yes' rendernode='/dev/dri/by-path/pci-0000:00:02.0-render'/> </graphics>
Spice supports variable compression settings for audio, images and streaming. These settings are accessible via the
compression
attribute in all following elements:image
to set image compression (acceptsauto_glz
,auto_lz
,quic
,glz
,lz
,off
),jpeg
for JPEG compression for images over wan (acceptsauto
,never
,always
),zlib
for configuring wan image compression (acceptsauto
,never
,always
) andplayback
for enabling audio stream compression (acceptson
oroff
). Since 0.9.1Streaming mode is set by the
streaming
element, settings itsmode
attribute to one offilter
,all
oroff
. Since 0.9.2Copy & Paste functionality (via Spice agent) is set by the
clipboard
element. It is enabled by default, and can be disabled by setting thecopypaste
property tono
. Since 0.9.3Mouse mode is set by the
mouse
element, setting itsmode
attribute to one ofserver
orclient
. If no mode is specified, the qemu default will be used (client mode). Since 0.9.11File transfer functionality (via Spice agent) is set using the
filetransfer
element. It is enabled by default, and can be disabled by setting theenable
property tono
. Since 1.2.2Spice may provide accelerated server-side rendering with OpenGL. You can enable or disable OpenGL support explicitly with the
gl
element, by setting theenable
property. (QEMU only, since 1.3.3 ). Note that this only works locally, since this requires usage of UNIX sockets, i.e. usinglisten
types 'socket' or 'none'. For accelerated OpenGL with remote support, consider pairing this element with typeegl-headless
(see below). However, this will deliver weaker performance compared to native Spice OpenGL support.By default, QEMU will pick the first available GPU DRM render node. You may specify a DRM render node path to use instead. (QEMU only, since 3.1.0 ).
rdp
Starts a RDP server. The
port
attribute specifies the TCP port number (with -1 as legacy syntax indicating that it should be auto-allocated). Theautoport
attribute is the new preferred syntax for indicating auto-allocation of the TCP port to use. In the VirtualBox driver, theautoport
will make the hypervisor pick available port from 3389-3689 range when the VM is started. The chosen port will be reflected in theport
attribute. ThemultiUser
attribute is a boolean deciding whether multiple simultaneous connections to the VM are permitted. ThereplaceUser
attribute is a boolean deciding whether the existing connection must be dropped and a new connection must be established by the VRDP server, when a new client connects in single connection mode.desktop
This value is reserved for VirtualBox domains for the moment. It displays a window on the host desktop, similarly to "sdl", but using the VirtualBox viewer. Just like "sdl", it accepts the optional attributes
display
andfullscreen
.egl-headless
Since 4.6.0This display type provides support for an OpenGL accelerated display accessible both locally and remotely (for comparison, Spice's native OpenGL support only works locally using UNIX sockets at the moment, but has better performance). Since this display type doesn't provide any window or graphical console like the other types, for practical reasons it should be paired with either
vnc
orspice
graphics types. This display type is only supported by QEMU domains (needs QEMU 2.10 or newer). 5.0.0 this element accepts a<gl/>
sub-element with an optional attributerendernode
which can be used to specify an absolute path to a host's DRI device to be used for OpenGL rendering.<graphics type='spice' autoport='yes'/> <graphics type='egl-headless'> <gl rendernode='/dev/dri/renderD128'/> </graphics>
dbus
Since 8.4.0Export the display over D-Bus. By default, it will use a private bus, except when
p2p
oraddress
are specified.<graphics type='dbus'/>
p2p
(acceptson
oroff
) enables peer-to-peer connections, established through virDomainOpenGraphics() APIs.address
(accepts a D-Bus address), will connect to the specified bus address.This element accepts a
<gl/>
sub-element with an optional attributerendernode
which can be used to specify an absolute path to a host's DRI device to be used for OpenGL rendering.Copy & Paste functionality is provided thanks to the QEMU clipboard manager and the SPICE vdagent protocol. See
qemu-vdagent
for more details.D-Bus can export an audio backend using the
<audio>
sub-element:<graphics type='dbus' ...> <audio id='1'> </graphics>
Where
1
is an id of the audio device (See Audio backends).
Graphics device uses a <listen>
to set up where the device should listen for clients. It has a mandatory attribute type
which specifies the listen type. Only vnc
, spice
and rdp
supports <listen>
element. Since 0.9.4 . Available types are:
address
Tells a graphics device to use an address specified in the
address
attribute, which will contain either an IP address or hostname (which will be resolved to an IP address via a DNS query) to listen on.It is possible to omit the
address
attribute in order to use an address from config files Since 1.3.5 .The
address
attribute is duplicated aslisten
attribute ingraphics
element for backward compatibility. If both are provided they must be equal.network
This is used to specify an existing network in the
network
attribute from libvirt's list of configured networks. The named network configuration will be examined to determine an appropriate listen address and the address will be stored in live XML inaddress
attribute. For example, if the network has an IPv4 address in its configuration (e.g. if it has a forward type ofroute
,nat
, or no forward type (isolated)), the first IPv4 address listed in the network's configuration will be used. If the network is describing a host bridge, the first IPv4 address associated with that bridge device will be used, and if the network is describing one of the 'direct' (macvtap) modes, the first IPv4 address of the first forward dev will be used.socket
since 2.0.0 (QEMU only)This listen type tells a graphics server to listen on unix socket. Attribute
socket
contains a path to unix socket. If this attribute is omitted libvirt will generate this path for you. Supported by graphics typevnc
andspice
.For
vnc
graphics be backward compatible thesocket
attribute of firstlisten
element is duplicated assocket
attribute ingraphics
element. Ifgraphics
element contains asocket
attribute alllisten
elements are ignored.none
since 2.0.0 (QEMU only)This listen type doesn't have any other attribute. Libvirt supports passing a file descriptor through our APIs virDomainOpenGraphics() and virDomainOpenGraphicsFD(). No other listen types are allowed if this one is used and the graphics device doesn't listen anywhere. You need to use one of the two APIs to pass a FD to QEMU in order to connect to this graphics device. Supported by graphics type
vnc
andspice
.
Video devices
A video device.
...
<devices>
<video>
<model type='vga' vram='16384' heads='1'>
<acceleration accel3d='yes' accel2d='yes'/>
</model>
<driver name='qemu'/>
</video>
</devices>
...
video
The
video
element is the container for describing video devices. For backwards compatibility, if novideo
is set but there is agraphics
in domain xml, then libvirt will add a defaultvideo
according to the guest type.For a guest of type "kvm", the default
video
is:type
with value "cirrus",vram
with value "16384" andheads
with value "1". By default, the first video device in domain xml is the primary one, but the optional attributeprimary
( since 1.0.2 ) with value 'yes' can be used to mark the primary in cases of multiple video device. The non-primary must be type of "qxl" or ( since 2.4.0 ) "virtio".model
The
model
element has a mandatorytype
attribute which takes the value "vga", "cirrus", "vmvga", "xen", "vbox", "qxl" ( since 0.8.6 ), "virtio" ( since 1.3.0 ), "gop" ( since 3.2.0 ), "bochs" ( since 5.6.0 ), "ramfb" ( since 5.9.0 ), or "none" ( since 4.6.0 ), depending on the hypervisor features available.Note: The purpose of the type
none
is to instruct libvirt not to add a default video device in the guest (see thevideo
element description above), since such behaviour is inconvenient in cases where GPU mediated devices are meant to be the only rendering device within a guest. If this is your use case specify anone
typevideo
device in the XML to stop the default behaviour. Refer to Host device assignment to see how to add a mediated device into a guest.You can provide the amount of video memory in kibibytes (blocks of 1024 bytes) using
vram
. This is supported only for guest type of "vz", "qemu", "kvm", "hvf", "vbox", "vmx" and "xen". If no value is provided the default is used. If the size is not a power of two it will be rounded to closest one.The number of screen can be set using
heads
. This is supported only for guests type of "vz", "kvm", "hvf", "vbox" and "vmx".For guest type of "kvm", "hvf" or "qemu" and model type "qxl" there are optional attributes. Attribute
ram
( since 1.0.2 ) specifies the size of the primary bar, while the attributevram
specifies the secondary bar size. Ifram
orvram
are not supplied a default value is used. Theram
should also be rounded to power of two asvram
. There is also optional attributevgamem
( since 1.2.11 ) to set the size of VGA framebuffer for fallback mode of QXL device. Attributevram64
( since 1.3.3 ) extends secondary bar and makes it addressable as 64bit memory.Since 5.9.0 , the
model
element may also have an optionalresolution
sub-element. Theresolution
element has attributesx
andy
to set the minimum resolution for the video device. This sub-element is valid for model types "vga", "qxl", "bochs", "gop", and "virtio".acceleration
Configure if video acceleration should be enabled.
accel2d
Enable 2D acceleration (for vbox driver only, since 0.7.1 )
accel3d
Enable 3D acceleration (for vbox driver since 0.7.1 , qemu driver since 1.3.0 )
rendernode
Absolute path to a host's DRI device to be used for rendering (for 'vhostuser' driver only, since 5.8.0 ). If none is specified, libvirt will pick one available.
address
The optional
address
sub-element can be used to tie the video device to a particular PCI slot. On S390,address
can be used to provide the CCW address for the video device ( since 4.2.0 ).driver
The subelement
driver
can be used to tune the device:name
Specify the backend driver to use, either "qemu" or "vhostuser" depending on the hypervisor features available ( since 5.8.0 ). "qemu" is the default QEMU backend. "vhostuser" will use a separate vhost-user process backend (for
virtio
device).- virtio options
Virtio-related options can also be set (Since 3.5.0)
- VGA configuration
Control how the video devices exposed to the guest using the
vgaconf
attribute which takes the value "io", "on" or "off". At present, it's only applicable to the bhyve's "gop" video model type ( Since 3.5.0 )
Consoles, serial, parallel & channel devices
A character device provides a way to interact with the virtual machine. Paravirtualized consoles, serial ports, parallel ports and channels are all classed as character devices and so represented using the same syntax.
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
<serial type='file'>
<source path='/tmp/file' append='on'>
<seclabel model='dac' relabel='no'/>
</source>
<target port='0'/>
</serial>
<console type='pty'>
<source path='/dev/pts/4'/>
<target port='0'/>
</console>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
</devices>
...
In each of these directives, the top-level element name (parallel, serial, console, channel) describes how the device is presented to the guest. The guest interface is configured by the target
element.
The interface presented to the host is given in the type
attribute of the top-level element. The host interface is configured by the source
element.
The source
element may contain an optional seclabel
to override the way that labelling is done on the socket path. If this element is not present, the security label is inherited from the per-domain setting.
If the interface type
presented to the host is "file", then the source
element may contain an optional attribute append
that specifies whether or not the information in the file should be preserved on domain restart. Allowed values are "on" and "off" (default). Since 1.3.1 .
Regardless of the type
, character devices can have an optional log file associated with them. This is expressed via a log
sub-element, with a file
attribute. There can also be an append
attribute which takes the same values described above. Since 1.3.3 .
...
<log file="/var/log/libvirt/qemu/guestname-serial0.log" append="off"/>
...
Each character device element has an optional sub-element <address>
which can tie the device to a particular controller (See Controllers) or PCI slot.
For character device with type unix
or tcp
the source
has an optional element reconnect
which configures reconnect timeout if the connection is lost. There are two attributes, enabled
where possible values are "yes" and "no" and timeout
which is in seconds. The reconnect
attribute is valid only for connect
mode. Since 3.7.0 (QEMU driver only) .
Guest interface
A character device presents itself to the guest as one of the following types.
Parallel port
...
<devices>
<parallel type='pty'>
<source path='/dev/pts/2'/>
<target port='0'/>
</parallel>
</devices>
...
target
can have a port
attribute, which specifies the port number. Ports are numbered starting from 0. There are usually 0, 1 or 2 parallel ports.
Serial port
...
<devices>
<!-- Serial port -->
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
<!-- Debug port for SeaBIOS / EDK II -->
<serial type='pty'>
<target type='isa-debug'/>
<address type='isa' iobase='0x402'/>
</console>
</devices>
...
...
<devices>
<!-- USB serial port -->
<serial type='pty'>
<target type='usb-serial' port='0'>
<model name='usb-serial'/>
</target>
<address type='usb' bus='0' port='1'/>
</serial>
</devices>
...
The target
element can have an optional port
attribute, which specifies the port number (starting from 0), and an optional type
attribute: valid values are, since 1.0.2 , isa-serial
(usable with x86 guests), usb-serial
(usable whenever USB support is available) and pci-serial
(usable whenever PCI support is available); since 3.10.0 , spapr-vio-serial
(usable with ppc64/pseries guests), system-serial
(usable with aarch64/virt and, since 4.7.0 , riscv/virt guests), sclp-serial
(usable with s390 and s390x guests) are available as well and since 8.1.0 isa-debug
(usable with x86 guests).
Since 3.10.0 , the target
element can have an optional model
subelement; valid values for its name
attribute are: isa-serial
(usable with the isa-serial
target type); usb-serial
(usable with the usb-serial
target type); pci-serial
(usable with the pci-serial
target type); spapr-vty
(usable with the spapr-vio-serial
target type); pl011
and, since 4.7.0 , 16550a
(usable with the system-serial
target type); sclpconsole
and sclplmconsole
(usable with the sclp-serial
target type). isa-debugcon
(usable with the isa-debug
target type); provides a virtual console for receiving debug messages from the firmware on x86 platforms. Since: 8.1.0. Providing a target model is usually unnecessary: libvirt will automatically pick one that's suitable for the chosen target type, and overriding that value is generally not recommended.
If any of the attributes is not specified by the user, libvirt will choose a value suitable for most users.
Most target types support configuring the guest-visible device address as documented in the Device Addresses section; more specifically, acceptable address types are isa
(for isa-serial
), usb
(for usb-serial
), pci
(for pci-serial
) and spapr-vio
(for spapr-vio-serial
). The system-serial
and sclp-serial
target types don't support specifying an address.
For the relationship between serial ports and consoles, refer to the Relationship between serial ports and consoles section.
Console
...
<devices>
<!-- Serial console -->
<console type='pty'>
<source path='/dev/pts/2'/>
<target type='serial' port='0'/>
</console>
</devices>
...
...
<devices>
<!-- KVM virtio console -->
<console type='pty'>
<source path='/dev/pts/5'/>
<target type='virtio' port='0'/>
</console>
</devices>
...
The console
element is used to represent interactive serial consoles. Depending on the type of guest in use and the specifics of the configuration, the console
element might represent the same device as an existing serial
element or a separate device.
A target
subelement is supported and works the same way as with the serial
element (See Serial port for details). Valid values for the type
attribute are: serial
(described below); virtio
(usable whenever VirtIO support is available); xen
, lxc
and openvz
(available when the corresponding hypervisor is in use). sclp
and sclplm
(usable for s390 and s390x QEMU guests) are supported for compatibility reasons but should not be used for new guests: use the sclpconsole
and sclplmconsole
target models, respectively, with the serial
element instead.
Of the target types listed above, serial
is special in that it doesn't represents a separate device, but rather the same device as the first serial
element. Due to this, there can only be a single console
element with target type serial
per guest.
Virtio consoles are usually accessible as /dev/hvc[0-7]
from inside the guest; for more information, see https://fedoraproject.org/wiki/Features/VirtioSerial. Since 0.8.3
For the relationship between serial ports and consoles, refer to the Relationship between serial ports and consoles section.
Relationship between serial ports and consoles
Due to historical reasons, the serial
and console
elements have partially overlapping scopes.
In general, both elements are used to configure one or more serial consoles to be used for interacting with the guest. The main difference between the two is that serial
is used for emulated, usually native, serial consoles, whereas console
is used for paravirtualized ones.
Both emulated and paravirtualized serial consoles have advantages and disadvantages:
- emulated serial consoles are usually initialized much earlier than paravirtualized ones, so they can be used to control the bootloader and display both firmware and early boot messages;
- on several platforms, there can only be a single emulated serial console per guest but paravirtualized consoles don't suffer from the same limitation.
A configuration such as:
...
<devices>
<console type='pty'>
<target type='serial'/>
</console>
<console type='pty'>
<target type='virtio'/>
</console>
</devices>
...
will work on any platform and will result in one emulated serial console for early boot logging / interactive / recovery use, and one paravirtualized serial console to be used eg. as a side channel. Most people will be fine with having just the first console
element in their configuration, but if a specific configuration is desired then both elements should be specified.
Note that, due to the compatibility concerns mentioned earlier, all the following configurations:
...
<devices>
<serial type='pty'/>
</devices>
...
...
<devices>
<console type='pty'/>
</devices>
...
...
<devices>
<serial type='pty'/>
<console type='pty'/>
</devices>
...
will be treated the same and will result in a single emulated serial console being available to the guest.
Channel
This represents a private communication channel between the host and the guest.
...
<devices>
<channel type='unix'>
<source mode='bind' path='/tmp/guestfwd'/>
<target type='guestfwd' address='10.0.2.1' port='4600'/>
</channel>
<!-- KVM virtio channel -->
<channel type='pty'>
<target type='virtio' name='arbitrary.virtio.serial.port.name'/>
</channel>
<channel type='unix'>
<source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
<target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
</channel>
<channel type='spicevmc'>
<target type='virtio' name='com.redhat.spice.0'/>
</channel>
</devices>
...
This can be implemented in a variety of ways. The specific type of channel is given in the type
attribute of the target
element. Different channel types have different target
attributes.
guestfwd
TCP traffic sent by the guest to a given IP address and port is forwarded to the channel device on the host. The
target
element must haveaddress
andport
attributes. Since 0.7.3virtio
Paravirtualized virtio channel. Channel is exposed in the guest under /dev/vport*, and if the optional element
name
is specified, /dev/virtio-ports/$name (for more info, please see https://fedoraproject.org/wiki/Features/VirtioSerial). The optional elementaddress
can tie the channel to a particulartype='virtio-serial'
controller, as documented in the Device Addresses section. With qemu, ifname
is "org.qemu.guest_agent.0", then libvirt can interact with a guest agent installed in the guest, for actions such as guest shutdown or file system quiescing. Since 0.7.7, guest agent interaction since 0.9.10 Moreover, since 1.0.6 it is possible to have source path auto generated for virtio unix channels. This is very useful in case of a qemu guest agent, where users don't usually care about the source path since it's libvirt who talks to the guest agent. In case users want to utilize this feature, they should leave<source>
element out. Since 1.2.11 the active XML for a virtio channel may contain an optionalstate
attribute that reflects whether a process in the guest is active on the channel. This is an output-only attribute. Possible values for thestate
attribute areconnected
anddisconnected
.xen
Paravirtualized Xen channel. Channel is exposed in the guest as a Xen console but identified with a name. Setup and consumption of a Xen channel depends on software and configuration in the guest. See the xen-pv-channel(7) man page for more information. Channel source path semantics are the same as the virtio target type. The
state
attribute is not supported since Xen channels lack the necessary probing mechanism. Since 2.3.0spicevmc
Paravirtualized SPICE channel. The domain must also have a SPICE server as a graphics device (See Graphical framebuffers), at which point the host piggy-backs messages across the
main
channel. Thetarget
element must be present, with attributetype='virtio'
; an optional attributename
controls how the guest will have access to the channel, and defaults toname='com.redhat.spice.0'
. The optionaladdress
element can tie the channel to a particulartype='virtio-serial'
controller. Since 0.8.8qemu-vdagent
Paravirtualized qemu vdagent channel. This channel implements the SPICE vdagent protocol, but is handled internally by qemu and therefore does not require a SPICE graphics device. Like the spicevmc channel, the
target
element must be present, with attributetype='virtio'
; an optional attributename
controls how the guest will have access to the channel, and defaults toname='com.redhat.spice.0'
. The optionaladdress
element can tie the channel to a particulartype='virtio-serial'
controller. Certain vdagent protocol features can by enabled or disabled using thesource
element.Copy & Paste functionality is set by the
clipboard
element. It is disabled by default, and can be enabled by setting thecopypaste
property toyes
. This allows the guest's clipboard to be synchronized with the qemu clipboard manager. This can enable copy and paste between a guest and a client when using a VNC graphics device (See Graphical framebuffers) (when using a VNC client that supports the copy/paste feature) or other graphics types that support the qemu clipboard manager.Mouse mode is set by the
mouse
element, setting itsmode
attribute to one ofserver
orclient
. If no mode is specified, the qemu default will be used (client mode). Since 8.4.0
Host interface
A character device presents itself to the host as one of the following types.
Domain logfile
This disables all input on the character device, and sends output into the virtual machine's logfile
...
<devices>
<console type='stdio'>
<target port='1'/>
</console>
</devices>
...
Device logfile
A file is opened and all data sent to the character device is written to the file.
...
<devices>
<serial type="file">
<source path="/var/log/vm/vm-serial.log"/>
<target port="1"/>
</serial>
</devices>
...
Virtual console
Connects the character device to the graphical framebuffer in a virtual console. This is typically accessed via a special hotkey sequence such as "ctrl+alt+3"
...
<devices>
<serial type='vc'>
<target port="1"/>
</serial>
</devices>
...
Null device
Connects the character device to the void. No data is ever provided to the input. All data written is discarded.
...
<devices>
<serial type='null'>
<target port="1"/>
</serial>
</devices>
...
Pseudo TTY
A Pseudo TTY is allocated using /dev/ptmx. A suitable client such as 'virsh console' can connect to interact with the serial port locally.
...
<devices>
<serial type="pty">
<source path="/dev/pts/3"/>
<target port="1"/>
</serial>
</devices>
...
NB special case if <console type='pty'>, then the TTY path is also duplicated as an attribute tty='/dev/pts/3' on the top level <console> tag. This provides compat with existing syntax for <console> tags.
Host device proxy
The character device is passed through to the underlying physical character device. The device types must match, eg the emulated serial port should only be connected to a host serial port - don't connect a serial port to a parallel port.
...
<devices>
<serial type="dev">
<source path="/dev/ttyS0"/>
<target port="1"/>
</serial>
</devices>
...
Named pipe
The character device writes output to a named pipe. See pipe(7) for more info.
...
<devices>
<serial type="pipe">
<source path="/tmp/mypipe"/>
<target port="1"/>
</serial>
</devices>
...
TCP client/server
The character device acts as a TCP client connecting to a remote server.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Or as a TCP server waiting for a client connection.
...
<devices>
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="raw"/>
<target port="1"/>
</serial>
</devices>
...
Alternatively you can use telnet
instead of raw
TCP in order to utilize the telnet protocol for the connection.
Since 0.8.5, some hypervisors support use of either telnets
(secure telnet) or tls
(via secure sockets layer) as the transport protocol for connections.
...
<devices>
<serial type="tcp">
<source mode="connect" host="0.0.0.0" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
...
<serial type="tcp">
<source mode="bind" host="127.0.0.1" service="2445"/>
<protocol type="telnet"/>
<target port="1"/>
</serial>
</devices>
...
Since 2.4.0, the optional attribute tls
can be used to control whether a chardev TCP communication channel would utilize a hypervisor configured TLS X.509 certificate environment in order to encrypt the data channel. For the QEMU hypervisor, usage of a TLS environment can be controlled on the host by the chardev_tls
and chardev_tls_x509_cert_dir
or default_tls_x509_cert_dir
settings in the file /etc/libvirt/qemu.conf. If chardev_tls
is enabled, then unless the tls
attribute is set to "no", libvirt will use the host configured TLS environment. If chardev_tls
is disabled, but the tls
attribute is set to "yes", then libvirt will attempt to use the host TLS environment if either the chardev_tls_x509_cert_dir
or default_tls_x509_cert_dir
TLS directory structure exists.
...
<devices>
<serial type="tcp">
<source mode='connect' host="127.0.0.1" service="5555" tls="yes"/>
<protocol type="raw"/>
<target port="0"/>
</serial>
</devices>
...
UDP network console
The character device acts as a UDP netconsole service, sending and receiving packets. This is a lossy service.
...
<devices>
<serial type="udp">
<source mode="bind" host="0.0.0.0" service="2445"/>
<source mode="connect" host="0.0.0.0" service="2445"/>
<target port="1"/>
</serial>
</devices>
...
UNIX domain socket client/server
The character device acts as a UNIX domain socket server, accepting connections from local clients.
...
<devices>
<serial type="unix">
<source mode="bind" path="/tmp/foo"/>
<target port="1"/>
</serial>
</devices>
...
Spice channel
The character device is accessible through spice connection under a channel name specified in the channel
attribute. Since 1.2.2
Note: depending on the hypervisor, spiceports might (or might not) be enabled on domains with or without spice graphics (See Graphical framebuffers).
...
<devices>
<serial type="spiceport">
<source channel="org.qemu.console.serial.0"/>
<target port="1"/>
</serial>
</devices>
...
Nmdm device
The nmdm device driver, available on FreeBSD, provides two tty devices connected together by a virtual null modem cable. Since 1.2.4
...
<devices>
<serial type="nmdm">
<source master="/dev/nmdm0A" slave="/dev/nmdm0B"/>
</serial>
</devices>
...
The source
element has these attributes:
master
Master device of the pair, that is passed to the hypervisor. Device is specified by a fully qualified path.
slave
Slave device of the pair, that is passed to the clients for connection to the guest console. Device is specified by a fully qualified path.
Sound devices
A virtual sound card can be attached to the host via the sound
element. Since 0.4.3
...
<devices>
<sound model='es1370'/>
</devices>
...
sound
The
sound
element has one mandatory attribute,model
, which specifies what real sound device is emulated. Valid values are specific to the underlying hypervisor, though typical choices are 'sb16', 'es1370', 'pcspk', 'ac97' (Since 0.6.0), 'ich6' (Since 0.8.8), 'ich9' (Since 1.1.3), 'usb' (Since 1.2.8) and 'ich7' (Since 6.7.0, bhyve only).
Since 0.9.13 , a sound element with ich6
or ich9
models can have optional sub-elements <codec>
to attach various audio codecs to the audio device. If not specified, a default codec will be attached to allow playback and recording.
Valid values are:
- 'duplex' - advertise a line-in and a line-out
- 'micro' - advertise a speaker and a microphone
- 'output' - advertise a line-out Since 4.4.0
...
<devices>
<sound model='ich6'>
<codec type='micro'/>
</sound>
</devices>
...
Each sound
element has an optional sub-element <address>
which can tie the device to a particular PCI slot. See Device Addresses.
A sound device could be optionally mapped to the specific host audio backend using the <audio>
sub-element:
...
<devices>
<sound model='ich7'>
<audio id='1'>
</sound>
</devices>
...
Where 1
is an id of the audio device (See Audio backends). If no ID is specified, then the default audio backend will be used. Since 6.7.0, bhyve; Since 7.2.0, qemu.
Audio backends
A virtual audio device corresponds to a host audio backend that is mapped to the guest sound device.
type
The required
type
attribute specifies audio backend type. Currently, the supported values are 'none', 'alsa', 'coreaudio', 'dbus', jack', 'oss', 'pulseaudio', 'sdl', 'spice', 'file'.id
Integer id of the audio device. Must be greater than 0.
timerPeriod
Timer period in microseconds. Must be greater than 0. If omitted, the lowest possible period is used.
All the backends support child element for configuring input and output properties
...
<devices>
<audio id='1' type='pulseaudio' timerPeriod='40'>
<input mixingEngine='yes' fixedSettings='yes' voices='1' bufferLength='100'>
<settings frequency='44100' channels='2' format='s16'/>
</input>
<output mixingEngine='yes' fixedSettings='yes' voices='2' bufferLength='100'>
<settings frequency='22050' channels='4' format='f32'/>
</output>
</audio>
</devices>
...
The input and output elements support the same set of attributes and elements
mixingEngine
Control whether the host mixing engine is used to convert between different audio formats and sampling rates. When the mixing engine is disabled it is possible to make use of improved audio formats such as 5.1/7.1. If not specified, a hypervisor default applies.
fixedSettings
Control whether the mixing engine can dynamically choose settings to minimize format conversion. This is only valid when the mixing engine is explicitly enabled.
voices
The number of voices voices to use, usually defaults to 1
bufferLength
The length of the audio buffer in microseconds. Default is backend specific.
The <input>
and <output>
elements may also permit backend specific options.
When fixed settings are enabled, the <settings>
child element is permitted with the following attributes.
frequency
The frequency in HZ, usually defaulting to 44100
channels
The number of channels, usually defaulting to 2. The permitted max number of channels is hypervisor specific.
format
The audio format, one of
s8
,u8
,s16
,u16
,s32
,u32
,f32
. The default is hypervisor specific.
Note: If no <audio/>
element is defined, and the graphics
element is set to either 'vnc' or 'sdl', the libvirtd or virtqemud process will honor the following environment variables:
SDL_AUDIODRIVER
Valid values are 'pulseaudio', 'esd', 'alsa' or 'arts'.
QEMU_AUDIO_DRV
Valid values are 'pa', 'none', 'alsa', 'coreaudio', 'jack', 'oss', 'sdl', 'spice' or 'wav'.
None audio backend
The 'none' audio backend is a dummy backend that does not connect to any host audio framework. It still allows a remote desktop server like VNC to send and receive audio though. This is the default backend when VNC graphics are enabled in QEMU.
Since 7.2.0, qemu
ALSA audio backend
The 'alsa' audio type uses the ALSA host audio device framework.
The following additional attributes are permitted on the <input>
and <output>
elements
dev
Path to the host device node to connect the backend to. A hypervisor specific default applies if not specified.
<audio id="1" type="alsa">
<input dev="/dev/dsp0"/>
<output dev="/dev/dsp1"/>
</audio>
Since 7.2.0, qemu
Coreaudio audio backend
The 'coreaudio' audio backend delegates to a CoreAudio host audio framework for input and output on macOS.
The following additional attributes are permitted on the <input>
and <output>
elements
bufferCount
The number of buffers. It is recommended to set the
bufferLength
attribute at the same time.
<audio id="1" type="coreaudio">
<input bufferCount="50"/>
<output bufferCount="42"/>
</audio>
Since 7.2.0, qemu
D-Bus audio backend
The 'dbus' audio backend does not connect to any host audio framework. It exports a D-Bus interface when associated with a D-Bus display.
Since 8.4.0, qemu
Jack audio backend
The 'jack' audio backend delegates to a Jack daemon for audio input and output.
The following additional attributes are permitted on the <input>
and <output>
elements
serverName
Select the Jack server instance to connect to.
clientName
The client name to identify as. The server may modify this to ensure uniqueness unless
exactName
is enabledconnectPorts
A regular expression of Jack client port names to monitor and connect to.
exactName
Use the exact
clientName
requested
<audio id="1" type="jack">
<input serverName="fish" clientName="food" connectPorts="system:capture_[13]" exactName="yes"/>
<output serverName="fish" clientName="food" connectPorts="system:playback_[13]" exactName="yes"/>
</audio>
Since 7.2.0, qemu
OSS audio backend
The 'oss' audio type uses the OSS host audio device framework.
The following additional attributes are permitted on the <audio>
element
tryMMap
Attempt to use mmap for data transfer
exclusive
Enforce exclusive access to the host device
dspPolicy
Set the timing policy of the device, values between -1 and 10. Smaller numbers result in lower latency but higher CPU usage. A negative value requests use of fragment mode.
The following additional attributes are permitted on the <input>
and <output>
elements
dev
Path to the host device node to connect the backend to. A hypervisor specific default applies if not specified.
bufferCount
The number of buffers. It is recommended to set the
bufferLength
attribute at the same time.tryPoll
Attempt to use polling mode
<audio type='oss' id='1' tryMMap='yes' exclusive='yes' dspPolicy='4'>
<input dev='/dev/dsp0' bufferCount='40' tryPoll='yes'/>
<output dev='/dev/dsp0' bufferCount='40' tryPoll='yes'/>
</audio>
Since 6.7.0, bhyve; Since 7.2.0, qemu
PulseAudio audio backend
The 'pulseaudio' audio backend delegates to a PulseAudio daemon audio input and output.
The following additional attributes are permitted on the <audio>
element
serverName
Hostname of the PulseAudio server
The following additional attributes are permitted on the <input>
and <output>
elements
name
The sink/source name to use
streamName
The name to identify the stream associated with the VM
latency
Desired latency for the server to target in microseconds
<audio id="1" type="pulseaudio" serverName="acme.example.org">
<input name="fish" streamName="food" latency="100"/>
<output name="fish" streamName="food" latency="200"/>
</audio>
Since 7.2.0, qemu
SDL audio backend
The 'sdl' audio backend delegates to the SDL library for audio input and output.
The following additional attributes are permitted on the <audio>
element
driver
SDL audio driver. The
name
attribute specifies SDL driver name, one of 'esd', 'alsa', 'arts', 'pulseaudio'.
The following additional attributes are permitted on the <input>
and <output>
elements
bufferCount
The number of buffers. It is recommended to set the
bufferLength
attribute at the same time.
<audio type='sdl' id='1' driver='pulseaudio'>
<input bufferCount='40'/>
<output bufferCount='40'/>
</audio>
Since 7.2.0, qemu
Spice audio backend
The 'spice' audio backend is similar to the 'none' backend in that it does not connect to any host audio framework. It exclusively allows a SPICE server to send and receive audio. This is the default backend when SPICE graphics are enabled in QEMU.
<audio type='spice' id='1'/>
Since 7.2.0, qemu
File audio backend
The 'file' audio backend is an output only driver which records audio to a file. The file format is implementation defined, and defaults to 'WAV' with QEMU.
<audio id="1" type="file" path="audio.wav"/>
Since 7.2.0, qemu
Watchdog device
A virtual hardware watchdog device can be added to the guest via the watchdog
element. Since 0.7.3, QEMU and KVM only
The watchdog device requires an additional driver and management daemon in the guest. Just enabling the watchdog in the libvirt configuration does not do anything useful on its own.
Currently libvirt does not support notification when the watchdog fires. This feature is planned for a future version of libvirt.
...
<devices>
<watchdog model='i6300esb'/>
</devices>
...
...
<devices>
<watchdog model='i6300esb' action='poweroff'/>
</devices>
</domain>
model
The required
model
attribute specifies what real watchdog device is emulated. Valid values are specific to the underlying hypervisor.QEMU and KVM support:
- 'i6300esb' - the recommended device, emulating a PCI Intel 6300ESB
- 'ib700' - emulating an ISA iBase IB700
- 'diag288' - emulating an S390 DIAG288 device Since 1.2.17
action
The optional
action
attribute describes what action to take when the watchdog expires. Valid values are specific to the underlying hypervisor.QEMU and KVM support:
- 'reset' - default, forcefully reset the guest
- 'shutdown' - gracefully shutdown the guest (not recommended)
- 'poweroff' - forcefully power off the guest
- 'pause' - pause the guest
- 'none' - do nothing
- 'dump' - automatically dump the guest Since 0.8.7
- 'inject-nmi' - inject a non-maskable interrupt into the guest Since 1.2.17
Note 1: the 'shutdown' action requires that the guest is responsive to ACPI signals. In the sort of situations where the watchdog has expired, guests are usually unable to respond to ACPI signals. Therefore using 'shutdown' is not recommended.
Note 2: the directory to save dump files can be configured by
auto_dump_path
in file /etc/libvirt/qemu.conf.
Memory balloon device
A virtual memory balloon device is added to all Xen and KVM/QEMU guests. It will be seen as memballoon
element. It will be automatically added when appropriate, so there is no need to explicitly add this element in the guest XML unless a specific PCI slot needs to be assigned. Since 0.8.3, Xen, QEMU and KVM only Additionally, since 0.8.4 , if the memballoon device needs to be explicitly disabled, model='none'
may be used.
Example: automatically added device with KVM
...
<devices>
<memballoon model='virtio'/>
</devices>
...
Example: manually added device with static PCI slot 2 requested
...
<devices>
<memballoon model='virtio'>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
<stats period='10'/>
<driver iommu='on' ats='on'/>
</memballoon>
</devices>
</domain>
model
The required
model
attribute specifies what type of balloon device is provided. Valid values are specific to the virtualization platform- 'virtio' - default with QEMU/KVM
- 'virtio-transitional' Since 5.2.0
- 'virtio-non-transitional' Since 5.2.0
- 'xen' - default with Xen
See Virtio transitional devices for more details.
autodeflate
The optional
autodeflate
attribute allows to enable/disable (values "on"/"off", respectively) the ability of the QEMU virtio memory balloon to release some memory at the last moment before a guest's process get killed by Out of Memory killer. Since 1.3.1, QEMU and KVM onlyfreePageReporting
The optional
freePageReporting
attribute allows to enable/disable ("on"/"off", respectively) the ability of the QEMU virtio memory balloon to return unused pages back to the hypervisor to be used by other guests or processes. Please note that despite its name it has no effect on free memory as reported byvirDomainMemoryStats()
and/orvirsh dommemstat
. Since 6.9.0, QEMU and KVM onlyperiod
The optional
period
allows the QEMU virtio memory balloon driver to provide statistics through thevirsh dommemstat [domain]
command. By default, collection is not enabled. In order to enable, use thevirsh dommemstat [domain] --period [number]
command orvirsh edit
command to add the option to the XML definition. Thevirsh dommemstat
will accept the options--live
,--current
, or--config
. If an option is not provided, the change for a running domain will only be made to the active guest. If the QEMU driver is not at the right revision, the attempt to set the period will fail. Large values (e.g. many years) might be ignored. Since 1.1.1, requires QEMU 1.5driver
For model
virtio
memballoon, Virtio-related options can also be set. ( Since 3.5.0 )
Random number generator device
The virtual random number generator device allows the host to pass through entropy to guest operating systems. Since 1.0.3
Example: usage of the RNG device:
...
<devices>
<rng model='virtio'>
<rate period="2000" bytes="1234"/>
<backend model='random'>/dev/random</backend>
<!-- OR -->
<backend model='egd' type='udp'>
<source mode='bind' service='1234'/>
<source mode='connect' host='1.2.3.4' service='1234'/>
</backend>
<!-- OR -->
<backend model='builtin'/>
</rng>
</devices>
...
model
The required
model
attribute specifies what type of RNG device is provided. Valid values are specific to the virtualization platform:- 'virtio' - supported by qemu and virtio-rng kernel module
- 'virtio-transitional' Since 5.2.0
- 'virtio-non-transitional' Since 5.2.0
See Virtio transitional devices for more details.
rate
The optional
rate
element allows limiting the rate at which entropy can be consumed from the source. The mandatory attributebytes
specifies how many bytes are permitted to be consumed per period. An optionalperiod
attribute specifies the duration of a period in milliseconds; if omitted, the period is taken as 1000 milliseconds (1 second). Since 1.0.4backend
The
backend
element specifies the source of entropy to be used for the domain. The source model is configured using themodel
attribute. Supported source models are:random
This backend type expects a non-blocking character device as input. The file name is specified as contents of the
backend
element. Since 1.3.4 any path is accepted. Before that/dev/random
and/dev/hwrng
were the only accepted paths. When no file name is specified, the hypervisor default is used. For QEMU, the default is/dev/random
. However, the recommended source of entropy is/dev/urandom
(as it doesn't have the limitations of/dev/random
).egd
This backend connects to a source using the EGD protocol. The source is specified as a character device. Refer to the Host interface for more information.
builtin
This backend uses qemu builtin random generator, which uses
getrandom()
syscall as the source of entropy. ( Since 6.1.0 and QEMU 4.2 )
driver
The subelement
driver
can be used to tune the device:- virtio options
Virtio-related options can also be set. ( Since 3.5.0 )
TPM device
The TPM device enables a QEMU guest to have access to TPM functionality. The TPM device may either be a TPM 1.2 or a TPM 2.0.
The TPM passthrough device type provides access to the host's TPM for one QEMU guest. No other software may be using the TPM device, typically /dev/tpm0, at the time the QEMU guest is started. 'passthrough' since 1.0.5
Example: usage of the TPM passthrough device
...
<devices>
<tpm model='tpm-tis'>
<backend type='passthrough'>
<device path='/dev/tpm0'/>
</backend>
</tpm>
</devices>
...
The emulator device type gives access to a TPM emulator providing TPM functionality for each VM. QEMU talks to it over a Unix socket. With the emulator device type each guest gets its own private TPM. 'emulator' since 4.5.0 The state of the TPM emulator can be encrypted by providing an encryption
element. 'encryption' since 5.6.0
Example: usage of the TPM Emulator
...
<devices>
<tpm model='tpm-tis'>
<backend type='emulator' version='2.0'>
<encryption secret='6dd3e4a5-1d76-44ce-961f-f119f5aad935'/>
<active_pcr_banks>
<sha256/>
</active_pcr_banks>
</backend>
</tpm>
</devices>
...
model
The
model
attribute specifies what device model QEMU provides to the guest. If no model name is provided,tpm-tis
will automatically be chosen for non-PPC64 architectures. Since 4.4.0 , another available choice is thetpm-crb
, which should only be used when the backend device is a TPM 2.0. Since 6.1.0 , pSeries guests on PPC64 are supported and the default istpm-spapr
. Since 6.5.0 , a new model calledspapr-tpm-proxy
was added for pSeries guests. This model only works with thepassthrough
backend. It creates a TPM Proxy device that communicates with an existing TPM Resource Manager in the host, for example/dev/tpmrm0
, enabling the guest to run in secure virtual machine mode with the help of an Ultravisor. Adding a TPM Proxy to a pSeries guest brings no security benefits unless the guest is running on a PPC64 host that has an Ultravisor and a TPM Resource Manager. Only one TPM Proxy device is allowed per guest, but a TPM Proxy device can be added together with other TPM devices.backend
The
backend
element specifies the type of TPM device. The following types are supported:passthrough
Use the host's TPM or TPM Resource Manager device.
This backend type requires exclusive access to a TPM device on the host. An example for such a device is /dev/tpm0. The fully qualified file name is specified by path attribute of the
source
element. If no file name is specified then /dev/tpm0 is automatically used. Since 6.5.0 , when choosing thespapr-tpm-proxy
model, the file name specified is expected to be a TPM Resource Manager device, e.g./dev/tpmrm0
.emulator
For this backend type the 'swtpm' TPM Emulator must be installed on the host. Libvirt will automatically start an independent TPM emulator for each QEMU guest requesting access to it.
version
The
version
attribute indicates the version of the TPM. This attribute only works with theemulator
backend. The following versions are supported:- '1.2' : creates a TPM 1.2
- '2.0' : creates a TPM 2.0
The default version used depends on the combination of hypervisor, guest architecture, TPM model and backend.
persistent_state
The
persistent_state
attribute indicates whether 'swtpm' TPM state is kept or not when a transient domain is powered off or undefined. This option can be used for preserving TPM state. By default the value isno
. This attribute only works with theemulator
backend. The accepted values areyes
andno
. Since 7.0.0active_pcr_banks
The
active_pcr_banks
node is used to define which of the PCR banks of a TPM 2.0 to activate. Valid names are for example sha1, sha256, sha384, and sha512. If this node is provided, the set of PCR banks are activated before every start of a VM and this step is logged in the swtpm's log. If this node is removed or omitted then libvirt will not modify the active PCR banks upon VM start but leave them at their last configuration. This attribute requires that swtpm_setup v0.7 or later is installed and may not have any effect otherwise. The selection of PCR banks only works with theemulator
backend. since:Since 7.10.0encryption
The
encryption
element allows the state of a TPM emulator to be encrypted. Thesecret
must reference a secret object that holds the passphrase from which the encryption key will be derived.
NVRAM device
nvram device is always added to pSeries guest on PPC64, and its address is allowed to be changed. Element nvram
(only valid for pSeries guest, since 1.0.5 ) is provided to enable the address setting.
Example: usage of NVRAM configuration
...
<devices>
<nvram>
<address type='spapr-vio' reg='0x00003000'/>
</nvram>
</devices>
...
spapr-vio
VIO device address type, only valid for PPC64.
reg
Device address
panic device
panic device enables libvirt to receive panic notification from a QEMU guest. Since 1.2.1, QEMU and KVM only
This feature is always enabled for:
- pSeries guests, since it's implemented by the guest firmware
- S390 guests, since it's an integral part of the S390 architecture
For the guest types listed above, libvirt automatically adds a panic
element to the domain XML.
Example: usage of panic configuration
...
<devices>
<panic model='hyperv'/>
<panic model='isa'>
<address type='isa' iobase='0x505'/>
</panic>
</devices>
...
model
The optional
model
attribute specifies what type of panic device is provided. The panic model used when this attribute is missing depends on the hypervisor and guest arch.- 'isa' - for ISA pvpanic device
- 'pseries' - default and valid only for pSeries guests.
- 'hyperv' - for Hyper-V crash CPU feature. Since 1.3.0, QEMU and KVM only
- 's390' - default for S390 guests. Since 1.3.5
address
address of panic. The default ioport is 0x505. Most users don't need to specify an address, and doing so is forbidden altogether for s390, pseries and hyperv models.
Shared memory device
A shared memory device allows to share a memory region between different virtual machines and the host. Since 1.2.10, QEMU and KVM only
...
<devices>
<shmem name='my_shmem0' role='peer'>
<model type='ivshmem-plain'/>
<size unit='M'>4</size>
</shmem>
<shmem name='shmem_server'>
<model type='ivshmem-doorbell'/>
<size unit='M'>2</size>
<server path='/tmp/socket-shmem'/>
<msi vectors='32' ioeventfd='on'/>
</shmem>
</devices>
...
shmem
The
shmem
element has one mandatory attribute,name
to identify the shared memory. This attribute cannot be directory specific to.
or..
as well as it cannot involve path separator/
.The optional
role
(since 6.6.0) attribute specifies the shared memory is migratable or not. The value can be either "master" or "peer", the former will mean that upon migration, the data in the shared memory is migrated with the domain. There should be only one "master" per shared memory object. Migration with "peer" role is disabled. If migration of such domain is required, the shmem device needs to be unplugged before migration and plugged in at the destination upon successful migration. If the role not specified, the hypervisor default is used. This attribute is currently available only formodel
typeivshmem-plain
andivshmem-doorbell
.model
Attribute
type
of the optional elementmodel
specifies the model of the underlying device providing theshmem
device. The models currently supported areivshmem
(supports both server and server-less shmem, but is deprecated by newer QEMU in favour of the -plain and -doorbell variants),ivshmem-plain
(only for server-less shmem) andivshmem-doorbell
(only for shmem with the server).size
The optional
size
element specifies the size of the shared memory. This must be power of 2 and greater than or equal to 1 MiB.server
The optional
server
element can be used to configure a server socket the device is supposed to connect to. The optionalpath
attribute specifies the absolute path to the unix socket and defaults to/var/lib/libvirt/shmem/$shmem-$name-sock
.msi
The optional
msi
element enables/disables (values "on"/"off", respectively) MSI interrupts. This option can currently be used only together with theserver
element. Thevectors
attribute can be used to specify the number of interrupt vectors. Theioeventd
attribute enables/disables (values "on"/"off", respectively) ioeventfd.
Memory devices
In addition to the initial memory assigned to the guest, memory devices allow additional memory to be assigned to the guest in the form of memory modules. A memory device can be hot-plugged or hot-unplugged depending on the guests' memory resource needs. Some hypervisors may require NUMA configured for the guest.
Example: usage of the memory devices
...
<devices>
<memory model='dimm' access='private' discard='yes'>
<target>
<size unit='KiB'>524287</size>
<node>0</node>
</target>
</memory>
<memory model='dimm'>
<source>
<pagesize unit='KiB'>2048</pagesize>
<nodemask>1-3</nodemask>
</source>
<target>
<size unit='KiB'>524287</size>
<node>1</node>
</target>
</memory>
<memory model='nvdimm'>
<uuid>9066901e-c90a-46ad-8b55-c18868cf92ae</uuid>
<source>
<path>/tmp/nvdimm</path>
</source>
<target>
<size unit='KiB'>524288</size>
<node>1</node>
<label>
<size unit='KiB'>128</size>
</label>
<readonly/>
</target>
</memory>
<memory model='nvdimm' access='shared'>
<uuid>e39080c8-7f99-4b12-9c43-d80014e977b8</uuid>
<source>
<path>/dev/dax0.0</path>
<alignsize unit='KiB'>2048</alignsize>
<pmem/>
</source>
<target>
<size unit='KiB'>524288</size>
<node>1</node>
<label>
<size unit='KiB'>128</size>
</label>
</target>
</memory>
<memory model='virtio-pmem' access='shared'>
<source>
<path>/tmp/virtio_pmem</path>
</source>
<target>
<size unit='KiB'>524288</size>
</target>
</memory>
<memory model='virtio-mem'>
<source>
<nodemask>1-3</nodemask>
<pagesize unit='KiB'>2048</pagesize>
</source>
<target>
<size unit='KiB'>2097152</size>
<node>0</node>
<block unit='KiB'>2048</block>
<requested unit='KiB'>1048576</requested>
<current unit='KiB'>524288</current>
</target>
</memory>
</devices>
...
model
Provide
dimm
to add a virtual DIMM module to the guest. Since 1.2.14 Providenvdimm
model that adds a Non-Volatile DIMM module. Since 3.2.0 Providevirtio-pmem
model to add a paravirtualized persistent memory device. Since 7.1.0 Providevirtio-mem
model to add paravirtualized memory device. Since 7.9.0access
An optional attribute
access
( since 3.2.0 ) that provides capability to fine tune mapping of the memory on per module basis. Values are the same as Memory Backing:shared
andprivate
. Fornvdimm
model, if using real NVDIMM DAX device as backend,shared
is required. Forvirtio-pmem
modelshared
is required.discard
An optional attribute
discard
( since 4.4.0 ) that provides capability to fine tune discard of data on per module basis. Accepted values areyes
andno
. The feature is described here: Memory Backing. This attribute is allowed only formodel='dimm'
.uuid
For pSeries guests, an uuid can be set to identify the nvdimm module. If absent, libvirt will generate an uuid automatically. This attribute is allowed only for
model='nvdimm'
for pSeries guests. Since 6.2.0source
For model
dimm
and modelvirtio-mem
this element is optional and allows to fine tune the source of the memory used for the given memory device. If the element is not provided defaults configured vianumatune
are used. If the element is provided, then the following optional elements can be provided:pagesize
This element can be used to override the default host page size used for backing the memory device. The configured value must correspond to a page size supported by the host.
nodemask
This element can be used to override the default set of NUMA nodes where the memory would be allocated.
For model
nvdimm
thesource
element is mandatory. The mandatory child elementpath
represents a path in the host that backs the nvdimm module in the guest. The following optional elements may be used:alignsize
The
alignsize
element defines the page size alignment used to mmap the address range for the backendpath
. If not supplied the host page size is used. For example, to mmap a real NVDIMM device a 2M-aligned page may be required, and host page size is 4KB, then we need to set this element to 2MB. Since 5.0.0pmem
If persistent memory is supported and enabled by the hypervisor in order to guarantee the persistence of writes to the vNVDIMM backend, then use the
pmem
element in order to utilize the feature. Since 5.0.0
For model
virtio-pmem
thesource
element is mandatory. The following optional elements may be used:path
Represents a path in the host that backs the virtio memory module in the guest. It is mandatory.
target
The mandatory
target
element configures the placement and sizing of the added memory from the perspective of the guest.The mandatory
size
subelement configures the size of the added memory as a scaled integer. Forvirtio-mem
this represents the maximum possible size exposed to the guest.The
node
subelement configures the guest NUMA node to attach the memory to. The element shall be used only if the guest has NUMA nodes configured.The following optional elements may be used:
label
For NVDIMM type devices one can use
label
and its subelementsize
to configure the size of namespaces label storage within the NVDIMM module. Thesize
element has usual meaning described in the Memory Allocation section.label
is mandatory for pSeries guests and optional for all other architectures. For QEMU domains the following restrictions apply:- the minimum label size is 128KiB,
- the remaining size (total-size - label-size), also called guest area, will be aligned to 4KiB as default. For pSeries guests, the guest area will be aligned down to 256MiB, and the minimum size of the guest area must be at least 256MiB.
readonly
The
readonly
element is used to mark the vNVDIMM as read-only. Only the real NVDIMM device backend can guarantee the guest write persistence, so other backend types should use thereadonly
element. Since 5.0.0block
For
virtio-mem
only. The size of an individual block, granularity of division of memory block. Must be power of two and at least equal to size of a transparent hugepage (2MiB on x84_64). The default is hypervisor dependent.requested
For
virtio-mem
only. The total size exposed to the guest. Must respectblock
granularity and be smaller than or equal tosize
.current
Active XML for
virtio-mem
model may containcurrent
element that reflects the current size of the corresponding virtio memory device. The element is formatted into live XML and never parsed, i.e. it is output-only element.
IOMMU devices
The iommu
element can be used to add an IOMMU device. Since 2.1.0
Example:
...
<devices>
<iommu model='intel'>
<driver intremap='on'/>
</iommu>
</devices>
...
model
Supported values are
intel
(for Q35 guests)smmuv3
(since 5.5.0, for ARM virt guests), andvirtio
(since 8.3.0, for Q35 and ARM virt guests).driver
The
driver
subelement can be used to configure additional options, some of which might only be available for certain IOMMU models:intremap
The
intremap
attribute with possible valueson
andoff
can be used to turn on interrupt remapping, a part of the VT-d functionality. Currently this requires split I/O APIC (<ioapic driver='qemu'/>
). Since 3.4.0 (QEMU/KVM only)caching_mode
The
caching_mode
attribute with possible valueson
andoff
can be used to turn on the VT-d caching mode (useful for assigned devices). Since 3.4.0 (QEMU/KVM only)eim
The
eim
attribute (with possible valueson
andoff
) can be used to configure Extended Interrupt Mode. A q35 domain with split I/O APIC (as described in Hypervisor features), and both interrupt remapping and EIM turned on for the IOMMU, will be able to use more than 255 vCPUs. Since 3.4.0 (QEMU/KVM only)iotlb
The
iotlb
attribute with possible valueson
andoff
can be used to turn on the IOTLB used to cache address translation requests from devices. Since 3.5.0 (QEMU/KVM only)aw_bits
The
aw_bits
attribute can be used to set the address width to allow mapping larger iova addresses in the guest. Since 6.5.0 (QEMU/KVM only)
Vsock
A vsock host/guest interface. The model
attribute defaults to virtio
. Since 5.2.0 model
can also be 'virtio-transitional' and 'virtio-non-transitional', see Virtio transitional devices for more details. The optional attribute address
of the cid
element specifies the CID assigned to the guest. If the attribute auto
is set to yes
, libvirt will assign a free CID automatically on domain startup. Since 4.4.0 The optional driver
element allows to specify virtio options, see Virtio-related options for more details. Since 7.1.0
...
<devices>
<vsock model='virtio'>
<cid auto='no' address='3'/>
</vsock>
</devices>
...
Security label
The seclabel
element allows control over the operation of the security drivers. There are three basic modes of operation, 'dynamic' where libvirt automatically generates a unique security label, 'static' where the application/administrator chooses the labels, or 'none' where confinement is disabled. With dynamic label generation, libvirt will always automatically relabel any resources associated with the virtual machine. With static label assignment, by default, the administrator or application must ensure labels are set correctly on any resources, however, automatic relabeling can be enabled if desired. 'dynamic' since 0.6.1, 'static' since 0.6.2, and 'none' since 0.9.10.
If more than one security driver is used by libvirt, multiple seclabel
tags can be used, one for each driver and the security driver referenced by each tag can be defined using the attribute model
Valid input XML configurations for the top-level security label are:
<seclabel type='dynamic' model='selinux'/>
<seclabel type='dynamic' model='selinux'>
<baselabel>system_u:system_r:my_svirt_t:s0</baselabel>
</seclabel>
<seclabel type='static' model='selinux' relabel='no'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='static' model='selinux' relabel='yes'>
<label>system_u:system_r:svirt_t:s0:c392,c662</label>
</seclabel>
<seclabel type='none'/>
If no 'type' attribute is provided in the input XML, then the security driver default setting will be used, which may be either 'none' or 'dynamic'. If a 'baselabel' is set but no 'type' is set, then the type is presumed to be 'dynamic'
When viewing the XML for a running guest with automatic resource relabeling active, an additional XML element, imagelabel
, will be included. This is an output-only element, so will be ignored in user supplied XML documents
type
Either
static
,dynamic
ornone
to determine whether libvirt automatically generates a unique security label or not.model
A valid security model name, matching the currently activated security model. Model
dac
is not available when guest is run by unprivileged user.relabel
Either
yes
orno
. This must always beyes
if dynamic label assignment is used. With static label assignment it will default tono
.label
If static labelling is used, this must specify the full security label to assign to the virtual domain. The format of the content depends on the security driver in use:
- SELinux: a SELinux context.
- AppArmor: an AppArmor profile.
- DAC: owner and group separated by colon. They can be defined both as user/group names or uid/gid. The driver will first try to parse these values as names, but a leading plus sign can used to force the driver to parse them as uid or gid.
baselabel
If dynamic labelling is used, this can optionally be used to specify the base security label that will be used to generate the actual label. The format of the content depends on the security driver in use. The SELinux driver uses only the
type
field of the baselabel in the generated label. Other fields are inherited from the parent process when using SELinux baselabels. (The example above demonstrates the use ofmy_svirt_t
as the value for thetype
field.)imagelabel
This is an output only element, which shows the security label used on resources associated with the virtual domain. The format of the content depends on the security driver in use
When relabeling is in effect, it is also possible to fine-tune the labeling done for specific source file names, by either disabling the labeling (useful if the file lives on NFS or other file system that lacks security labeling) or requesting an alternate label (useful when a management application creates a special label to allow sharing of some, but not all, resources between domains), since 0.9.9 . When a seclabel
element is attached to a specific path rather than the top-level domain assignment, only the attribute relabel
or the sub-element label
are supported. Additionally, since 1.1.2 , an output-only element labelskip
will be present for active domains on disks where labeling was skipped due to the image being on a file system that lacks security labeling.
Key Wrap
The content of the optional keywrap
element specifies whether the guest will be allowed to perform the S390 cryptographic key management operations. A clear key can be protected by encrypting it under a unique wrapping key that is generated for each guest VM running on the host. Two variations of wrapping keys are generated: one version for encrypting protected keys using the DEA/TDEA algorithm, and another version for keys encrypted using the AES algorithm. If a keywrap
element is not included, the guest will be granted access to both AES and DEA/TDEA key wrapping by default.
<domain>
...
<keywrap>
<cipher name='aes' state='off'/>
</keywrap>
...
</domain>
At least one cipher
element must be nested within the keywrap
element.
cipher
The
name
attribute identifies the algorithm for encrypting a protected key. The values supported for this attribute areaes
for encryption under the AES wrapping key, ordea
for encryption under the DEA/TDEA wrapping key. Thestate
attribute indicates whether the cryptographic key management operations should be turned on for the specified encryption algorithm. The value can be set toon
oroff
.
Note: DEA/TDEA is synonymous with DES/TDES.
Launch Security
Specifying <launchSecurity type='s390-pv'/>
in a s390 domain prepares the guest to run in protected virtualization secure mode, also known as IBM Secure Execution. For more required host and guest preparation steps, see Protected Virtualization on s390 Since 7.6.0
The contents of the <launchSecurity type='sev'>
element is used to provide the guest owners input used for creating an encrypted VM using the AMD SEV feature (Secure Encrypted Virtualization). SEV is an extension to the AMD-V architecture which supports running encrypted virtual machine (VMs) under the control of KVM. Encrypted VMs have their pages (code and data) secured such that only the guest itself has access to the unencrypted version. Each encrypted VM is associated with a unique encryption key; if its data is accessed to a different entity using a different key the encrypted guests data will be incorrectly decrypted, leading to unintelligible data. For more information see various input parameters and its format see the SEV API spec Since 4.4.0
<domain>
...
<launchSecurity type='sev' kernelHashes='yes'>
<policy>0x0001</policy>
<cbitpos>47</cbitpos>
<reducedPhysBits>1</reducedPhysBits>
<dhCert>RBBBSDDD=FDDCCCDDDG</dhCert>
<session>AAACCCDD=FFFCCCDSDS</session>
</launchSecurity>
...
</domain>
kernelHashes
The optional
kernelHashes
attribute indicates whether the hashes of the kernel, ramdisk and command line should be included in the measurement done by the firmware. This is only valid if using direct kernel boot. Since 8.0.0cbitpos
The required
cbitpos
element provides the C-bit (aka encryption bit) location in guest page table entry. The value ofcbitpos
is hypervisor dependent and can be obtained through thesev
element from the domain capabilities.reducedPhysBits
The required
reducedPhysBits
element provides the physical address bit reducation. Similar tocbitpos
the value ofreduced-phys-bit
is hypervisor dependent and can be obtained through thesev
element from the domain capabilities.policy
The required
policy
element provides the guest policy which must be maintained by the SEV firmware. This policy is enforced by the firmware and restricts what configuration and operational commands can be performed on this guest by the hypervisor. The guest policy provided during guest launch is bound to the guest and cannot be changed throughout the lifetime of the guest. The policy is also transmitted during snapshot and migration flows and enforced on the destination platform. The guest policy is a 4 unsigned byte with the fields shown in Table:Bit(s) Description 0 Debugging of the guest is disallowed when set 1 Sharing keys with other guests is disallowed when set 2 SEV-ES is required when set 3 Sending the guest to another platform is disallowed when set 4 The guest must not be transmitted to another platform that is not in the domain when set. 5 The guest must not be transmitted to another platform that is not SEV capable when set. 6:15 reserved 16:32 The guest must not be transmitted to another platform with a lower firmware version. dhCert
The optional
dhCert
element provides the guest owners base64 encoded Diffie-Hellman (DH) key. The key is used to negotiate a master secret key between the SEV firmware and guest owner. This master secret key is then used to establish a trusted channel between SEV firmware and guest owner.session
The optional
session
element provides the guest owners base64 encoded session blob defined in the SEV API spec. See SEV spec LAUNCH_START section for the session blob format.
Example configs
Example configurations for each driver are provide on the driver specific pages listed below