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
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", "qemu", "lxc" and "kqemu". The
second attribute is id which is a unique
integer identifier for the running guest machine. Inactive
machines have no id value.
<domain type='xen' id='3'>
<name>fv0</name>
<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
<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>
...
namename element provides
a short name for the virtual machine. This name should
consist only of alpha-numeric 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 0.0.1uuiduuid element provides
a globally unique identifier for the virtual machine.
The format must be RFC 4122 compliant,
eg 3e3fce45-4f53-4fa7-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 sysinfo
specification. Since 0.0.1, sysinfo
since 0.8.7titletitle provides space for a
short description of the domain. The title should not contain
any newlines. Since 0.9.10.descriptiondescription 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 0.7.2metadatametadata 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 0.9.10There are a number of different ways to boot virtual machines each with their own pros and cons.
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.
...
<os>
<type>hvm</type>
<loader readonly='yes' type='rom'>/usr/lib/xen/boot/hvmloader</loader>
<nvram template='/usr/share/OVMF/OVMF_VARS.fd'>/var/lib/libvirt/nvram/guest_VARS.fd</nvram>
<boot dev='hd'/>
<boot dev='cdrom'/>
<bootmenu enable='yes' timeout='3000'/>
<smbios mode='sysinfo'/>
<bios useserial='yes' rebootTimeout='0'/>
</os>
...
typetype 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,
and machine referring to the machine
type. The Capabilities XML
provides details on allowed values for
these. Since 0.0.1loaderloader tag refers to a firmware blob
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 are
yes and no) to reflect the fact that the
image should be writable or read-only. The second attribute
type accepts values rom and
pflash. 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 be
pflash.nvramqemu.conf. If needed, the template
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 1.2.8bootdev attribute takes one of the values "fd", "hd",
"cdrom" or "network" and is used to specify the next boot device
to consider. The boot 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 disks,
network interfaces, and
USB and PCI devices sections below) were
introduced and they are the preferred way providing full control over
booting order. The boot element and per-device boot
elements are mutually exclusive. Since 0.1.3,
per-device boot since 0.8.8
smbiosmode 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 sysinfo 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.
bootmenuenable attribute can be either "yes" or "no".
If not specified, the hypervisor default is used.
Since 0.8.3
Additional attribute timeout 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 unless enable
is set to "yes". Since 1.2.8
biosuseserial with possible
values yes or no. 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 of 65535 and special
value -1 disables the reboot.
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> ...
bootloaderbootloader 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_argsbootloader_args element allows
command line arguments to be passed to the bootloader.
Since 0.2.3
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>
</os>
...
typeloaderkernelinitrdcmdlinedtb
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.
<os>
<type arch='x86_64'>exe</type>
<init>/bin/systemd</init>
<initarg>--unit</initarg>
<initarg>emergency.service</initarg>
</os>
If you want to enable user namespace, set the idmap element.
The uid and gid elements have three attributes:
starttargetcount
<idmap>
<uid start='0' target='1000' count='10'/>
<gid start='0' target='1000' count='10'/>
</idmap>
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>
</sysinfo>
...
The sysinfo element has a mandatory
attribute type that determine the layout of
sub-elements, with supported values of:
smbiossmbios sub-element of
the os element. Each
sub-element of sysinfo names a SMBIOS block, and
within those elements can be a list of entry
elements that describe a field within the block. The following
blocks and entries are recognized:
biosvendorversiondatereleasesystemmanufacturerproductversionserialuuiduuid element,
then the two values must match.skufamilybios
or system blocks will be ignored without error.
Other than uuid validation and date
format checking, all values are passed as strings to the
hypervisor driver.
<domain> ... <vcpu placement='static' cpuset="1-4,^3,6" current="1">2</vcpu> ... </domain>
vcpucpusetcpuset 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 by
cputune. If the attribute emulatorpin
of cputune is specified, the cpuset
specified by vcpu here will be ignored. Similarly,
for virtual CPUs which have the vcpupin specified,
the cpuset specified by cpuset here
will be ignored. For virtual CPUs which don't have
vcpupin specified, each will be pinned to the physical
CPUs specified by cpuset 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 0.4.4
currentcurrent can
be used to specify whether fewer than the maximum number of
virtual CPUs should be enabled.
Since 0.8.5
placementplacement can be used to
indicate the CPU placement mode for domain process. The value can
be either "static" or "auto", but defaults to placement
of numatune or "static" if cpuset is
specified. Using "auto" indicates the domain process will be pinned
to the advisory nodeset from querying numad and the value of
attribute cpuset will be ignored if it's specified.
If both cpuset and placement are not
specified or if placement is "static", but no
cpuset is specified, the domain process will be
pinned to all the available physical CPUs.
Since 0.9.11 (QEMU and KVM only)
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>
iothreads
<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>
<emulator_period>1000000</emulator_period>
<emulator_quota>-1</emulator_quota>
<vcpusched vcpus='0-4,^3' scheduler='fifo' priority='1'/>
<iothreadsched iothreads='2' scheduler='batch'/>
</cputune>
...
</domain>
cputunecputune element provides details
regarding the cpu tunable parameters for the domain.
Since 0.9.0
vcpupinvcpupin element specifies which of host's
physical CPUs the domain VCPU will be pinned to. If this is omitted,
and attribute cpuset of element vcpu is
not specified, the vCPU is pinned to all the physical CPUs by default.
It contains two required attributes, the attribute vcpu
specifies vcpu id, and the attribute cpuset is same as
attribute cpuset of element vcpu.
(NB: Only qemu driver support)
Since 0.9.0
emulatorpinemulatorpin 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 attribute
cpuset of element vcpu is not specified,
"emulator" is pinned to all the physical CPUs by default. It contains
one required attribute cpuset specifying which physical
CPUs to pin to.
iothreadpiniothreadpin element specifies which of host
physical CPUs the IOThreads will be pinned to. If this is omitted
and attribute cpuset of element vcpu is
not specified, the IOThreads are pinned to all the physical CPUs
by default. There are two required attributes, the attribute
iothread specifies the IOThread id and the attribute
cpuset specifying which physical CPUs to pin to. The
iothread value begins at "1" through the number of
iothreads
allocated to the domain. A value of "0" is not permitted.
Since 1.2.9
sharesshares 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.
Since 0.9.0
periodperiod element specifies the enforcement
interval(unit: microseconds). Within period, each vcpu of
the domain will not be allowed to consume more than 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 0.9.4, LXC since
0.9.10
quotaquota element specifies the maximum allowed
bandwidth(unit: microseconds). A domain with 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, 18446744073709551] 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
0.9.10
emulator_periodemulator_period element specifies the enforcement
interval(unit: microseconds). Within emulator_period, emulator
threads(those excluding vcpus) of the domain will not be allowed to consume
more than emulator_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 0.10.0
emulator_quotaemulator_quota element specifies the maximum
allowed bandwidth(unit: microseconds) for domain's emulator threads(those
excluding vcpus). A domain with emulator_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, 18446744073709551] or less than 0. A
quota with value 0 means no value.
Only QEMU driver support since 0.10.0
vcpusched and iothreadschedvcpusched elements specifies the scheduler
type (values batch, idle, fifo,
rr) for particular vCPU/IOThread threads (based on
vcpus and iothreads, leaving out
vcpus/iothreads sets the default). 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 1.2.13
<domain> ... <memory unit='KiB'>524288</memory> <currentMemory unit='KiB'>524288</currentMemory> ... </domain>
memoryunit, 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 the case of crash, optional attribute dumpCore
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)currentMemorymemory element.
The unit attribute behaves the same as
for memory.
<domain>
...
<memoryBacking>
<hugepages>
<page size="1" unit="G" nodeset="0-3,5"/>
<page size="2" unit="M" nodeset="4"/>
</hugepages>
<nosharepages/>
<locked/>
</memoryBacking>
...
</domain>
The optional memoryBacking element may contain several
elements that influence how virtual memory pages are backed by host
pages.
hugepagespage element is
introduced. It has one compulsory attribute size which
specifies which hugepages should be used (especially useful on systems
supporting hugepages of different sizes). The default unit for the
size attribute is kilobytes (multiplier of 1024). If you
want to use different unit, use optional unit attribute.
For systems with NUMA, the optional nodeset 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
this.nosharepageslockedhard_limit memory tuning
element to be used and set to the maximum memory configured for the
domain plus any memory consumed by the QEMU process itself.
Since 1.0.6
<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>
memtunememtune 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_limithard_limit element is the maximum memory
the guest can use. The units for this value are kibibytes (i.e. blocks
of 1024 bytes). However, 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. To determine the memory needed for a process
to run is an
undecidable problem.soft_limitsoft_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_limitswap_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_guaranteemin_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.
<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>
numatunenumatune 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 0.9.3
memorymemory element specifies how to allocate memory
for the domain process on a NUMA host. It contains several optional
attributes. Attribute mode is either 'interleave',
'strict', or 'preferred', defaults to 'strict'. Attribute
nodeset specifies the NUMA nodes, using the same syntax as
attribute cpuset of element vcpu. Attribute
placement (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 to placement of
vcpu, or "static" if nodeset is specified.
"auto" indicates the domain process will only allocate memory from the
advisory nodeset returned from querying numad, and the value of attribute
nodeset will be ignored if it's specified.
If placement of vcpu is 'auto', and
numatune is not specified, a default numatune
with placement 'auto' and mode 'strict' will
be added implicitly.
Since 0.9.3
memnodememnode elements can specify memory allocation
policies per each guest NUMA node. For those nodes having no
corresponding memnode element, the default from
element memory will be used. Attribute cellid
addresses guest NUMA node for which the settings are applied.
Attributes mode and nodeset have the same
meaning and syntax as in memory element.
This setting is not compatible with automatic placement.
QEMU Since 1.2.7
<domain>
...
<blkiotune>
<weight>800</weight>
<device>
<path>/dev/sda</path>
<weight>1000</weight>
</device>
<device>
<path>/dev/sdb</path>
<weight>500</weight>
</device>
</blkiotune>
...
</domain>
blkiotuneblkiotune 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 0.8.8weightweight 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].devicedevice elements
that further tune the weights for each host block device in
use by the domain. Note that
multiple guest disks 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 which can apply to an
individual <disk>).
Each device element has two
mandatory sub-elements, path describing the
absolute path of the device, and weight 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
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 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
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' cores='2' threads='1'/>
<feature policy='disable' name='lahf_lm'/>
</cpu>
...
<cpu mode='host-model'>
<model fallback='forbid'/>
<topology sockets='1' cores='2' threads='1'/>
</cpu>
...
<cpu mode='host-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' cores='2' threads='1'/>
</cpu>
...
cpucpu element is the main container for describing
guest CPU requirements. Its match attribute specified how
strictly has the virtual CPU provided to the guest match these
requirements. Since 0.7.6 the
match attribute can be omitted if topology
is the only element within cpu. Possible values for the
match attribute are:
minimumexactstrictmatch
attribute can be omitted and will default to exact.
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 the
mode attribute are:
customcpu element describes the CPU
that should be presented to the guest. This is the default when no
mode 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-modelhost-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. The
match attribute can't be used in this mode. Specifying
CPU model is not supported either, but model's
fallback attribute may still be used. Using the
feature 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 even if the destination host contains more capable CPUs for
the running instance of the guest; but shutting down and restarting
the guest may present different hardware to the guest according to
the capabilities of the new host. Beware, due to the
way libvirt detects host CPU and due to the fact libvirt does not
talk to QEMU/KVM when creating the CPU model, CPU configuration
created using host-model may not work as expected. The
guest CPU may differ from the configuration and it may also confuse
guest OS by using a combination of CPU features and other parameters
(such as CPUID level) that don't work. Until these issues are fixed,
it's a good idea to avoid using host-model and use
custom mode with just the CPU model from 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 the
host-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-passthroughfeature elements.host-model and host-passthrough
mode, the real (approximate in host-passthrough mode) CPU
definition which would be used on current host can be determined by
specifying VIR_DOMAIN_XML_UPDATE_CPU flag when calling
virDomainGetXMLDesc API. When running a guest that might
be prone to operating system reactivation when presented with
different hardware, and which will be migrated between hosts with
different capabilities, you can use this output to rewrite XML to the
custom mode for more robust migration.
modelmodel element specifies CPU model
requested by the guest. The list of available CPU models and their
definition can be found in cpu_map.xml file 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 optional
fallback 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 for fallback
attribute are: allow (this is the default), and
forbid. The optional vendor_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".vendorvendor 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 in cpu_map.xml.topologytopology element specifies requested topology of
virtual CPU provided to the guest. Three non-zero values have to be
given for sockets, cores, and
threads: total number of CPU sockets, number of cores per
socket, and number of threads per core, respectively.featurecpu element can contain zero or more
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 each feature
element depends on its policy attribute, which has to be
set to one of the following values:
forcerequireoptionaldisableforbidpolicy
attribute can be omitted and will default to require.
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'/>
<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. memory specifies the node memory
in kibibytes (i.e. blocks of 1024 bytes).
Since 1.2.11 one can use an additional unit attribute 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 ids 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.
This guest NUMA specification is currently available only for QEMU/KVM.
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_poweroffon_rebooton_crashEach of these states allow for the same four possible actions.
destroyrestartpreserverename-restart
QEMU/KVM supports the on_poweroff and on_reboot
events handling the destroy and restart actions.
The preserve action for an on_reboot event
is treated as a destroy and the rename-restart
action for an on_poweroff event is treated as a
restart event.
The on_crash event supports these additional
actions since 0.8.4.
coredump-destroycoredump-restart
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.
poweroffrestartpauseignoreSince 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>
...
pmHypervisors may allow certain CPU / machine features to be toggled on/off.
...
<features>
<pae/>
<acpi/>
<apic/>
<hap/>
<privnet/>
<hyperv>
<relaxed state='on'/>
<vapic state='on'/>
<spinlocks state='on' retries='4096'/>
</hyperv>
<kvm>
<hidden state='on'/>
</kvm>
<pvspinlock/>
</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,
but a common set for fully virtualized domains are:
paeacpiapiceoi with values on
and off which toggles the availability of EOI (End of
Interrupt) for the guest.
hapviridianprivnethyperv| Feature | Description | Value | Since |
|---|---|---|---|
| relaxed | Relax constraints on timers | on, off | 1.0.0 (QEMU only) |
| vapic | Enable virtual APIC | on, off | 1.1.0 (QEMU only) |
| spinlocks | Enable spinlock support | on, off; retries - at least 4095 | 1.1.0 (QEMU only) |
pvspinlockstate='off'
attribute.
kvm| Feature | Description | Value | Since |
|---|---|---|---|
| hidden | Hide the KVM hypervisor from standard MSR based discovery | on, off | 2.1.0 (QEMU only) |
pmustate attribute (values on,
off, default on) enable or disable the
performance monitoring unit for the guest.
Since 1.2.12
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>
...
clockThe 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.
utcadjustment 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 default adjustment is
hypervisor specific.
localtimeadjustment
attribute behaves the same as in 'utc' mode.
timezonetimezone attribute.
Since 0.7.7
variablebasis
attribute. The delta relative to UTC (or localtime) is specified
in seconds, using the adjustment 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 the basis
attribute can be either 'utc' (default) or 'localtime'.
A clock may have zero or more
timer sub-elements. Since
0.8.0
timer
Each timer element requires a name attribute,
and has other optional attributes that depend on
the name specified. Various hypervisors
support different combinations of attributes.
namename attribute selects which timer is
being modified, and can be one of
"platform" (currently unsupported),
"hpet" (libxl, xen, qemu), "kvmclock" (qemu),
"pit" (qemu), "rtc" (qemu), "tsc" (libxl) or "hypervclock"
(qemu - since 1.2.2).
The hypervclock timer adds support for the
reference time counter and the reference page for iTSC
feature for guests running the Microsoft Windows
operating system.
tracktrack attribute specifies what the timer
tracks, and can be "boot", "guest", or "wall".
Only valid for name="rtc"
or name="platform".
tickpolicy
The tickpolicy attribute determines what
happens when QEMU misses a deadline for injecting a
tick to the guest:
delaycatchupmergediscardIf the policy is "catchup", there can be further details in
the catchup sub-element.
catchupcatchup element has three optional
attributes, each a positive integer. The attributes
are threshold, slew,
and limit.
Note that hypervisors are not required to support all policies across all time sources
frequencyfrequency attribute is an unsigned
integer specifying the frequency at
which name="tsc" runs.
modemode attribute controls how
the name="tsc" timer is managed, and can be
"auto", "native", "emulate", "paravirt", or "smpsafe".
Other timers are always emulated.
presentpresent attribute can be "yes" or "no" to
specify whether a particular timer is available to the guest.
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>
...
emulatoremulator 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.
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"/>
</source>
<target dev="hdc" bus="ide"/>
<auth username='myuser'>
<secret type='ceph' usage='mypassid'/>
</auth>
</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">
<host name="hostname" port="80"/>
</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"/>
</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'/>
<readonly/>
</disk>
<disk type='block' device='lun'>
<driver name='qemu' type='raw'/>
<source dev='/dev/sda'/>
<target dev='sda' bus='scsi'/>
<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'/>
</source>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
<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'/>
</source>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
<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'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
<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'/>
<auth username='myuser'>
<secret type='iscsi' usage='libvirtiscsi'/>
</auth>
<target dev='vdc' bus='virtio'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<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>
</devices>
...
diskdisk element is the main container for describing
disks (since 0.0.3).
type attribute
since 0.0.3device attribute
since 0.1.4Using "lun" (since 0.9.10) is only valid when type is "block" or "network" using the iSCSI protocol, and 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').
rawio attribute
since 0.9.10rawio 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 than rawio.
sgio attribute
since 1.0.2rawio,
sgio is only valid for device 'lun'.
snapshot attribute
since 0.9.5snapshot='yes' with a transient disk generally
does not make sense.
sourcesource depends on the
disk type attribute value as follows:
type='file'
since 0.0.3file attribute specifies the fully-qualified
path to the file holding the disk.
type='block'
since 0.0.3dev attribute specifies the path to the
host device to serve as the disk.
type='dir'
since 0.7.5dir attribute specifies the fully-qualified path
to the directory to use as the disk.
type='network'
since 0.8.7protocol attribute specifies the protocol to
access to the requested image. Possible values are "nbd",
"iscsi", "rbd", "sheepdog" or "gluster". If the
protocol attribute is "rbd", "sheepdog" or
"gluster", an additional attribute name is
mandatory to specify which volume/image will be used. For "nbd",
the name attribute is optional. 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.
type='volume'
since 1.0.5pool and volume. Attribute
pool specifies the name of the
storage pool (managed
by libvirt) where the disk source resides. Attribute
volume specifies the name of storage volume (managed
by libvirt) used as the disk source. The value for the
volume attribute will be the output from the "Name"
column of a virsh 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". If mode is not specified,
the default is to use "host".
Using "direct" as the mode value indicates to use
the storage pool's
source element host 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 the mode 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').
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 contain the following sub elements:
host
When the disk type is "network", the source
may have zero or more host sub-elements used to
specify the hosts to connect.
The host 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 | 6789 |
| sheepdog | one of the sheepdog servers (default is localhost:7000) | zero or one | 7000 |
| gluster | a server running glusterd daemon | only one | 24007 |
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.
snapshotname attribute of snapshot 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).
configfile attribute for the config 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).
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 the
startupPolicy 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.
backingStoresource element. It is currently ignored on input
and only used for output to describe the detected backing chains.
Since 1.2.4. An empty
backingStore element means the sibling source is
self-contained and is not based on any backing store. The following
attributes and sub-elements are supported in
backingStore:
type attributetype attribute represents the type of disk used
by the backing store, see disk type attribute above for more
details and possible values.
index attributevirDomainBlockRebase API). For example,
vda[2] refers to the backing store with
index='2' of the disk with vda target.
format sub-elementformat element contains type
attribute which specifies the internal format of the backing
store, such as raw or qcow2.
source sub-elementsource
element in disk. It specifies which file, device,
or network location contains the data of the described backing
store.
backingStore sub-elementbackingStore
element.
mirrorsource sub-element will eventually have the
same contents as the source, and with the file format in the
sub-element format (which might differ from the
format of the source). The details of the source
sub-element are determined by the type attribute
of the mirror, similar to what is done for the
overall disk device element. The job
attribute mentions which API started the operation ("copy" for
the virDomainBlockRebase API, or "active-commit"
for the virDomainBlockCommit
API), since 1.2.7. The
attribute ready, if present, tracks progress of
the job: yes if the disk is known to be ready to
pivot, or, since
1.2.7, abort or pivot if the
job is in the process of completing. If ready is
not present, the disk is probably still
copying. For now, this element only valid in output; it is
ignored on input. The source 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 attributes file
and format in the mirror element.
targettarget element controls the bus / device
under which the disk is exposed to the guest
OS. The dev 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 optional bus
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
attribute tray 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 of
tray could be updated while the domain is running.
The optional attribute removable sets the
removable flag for USB disks, and its value can be either "on"
or "off", defaulting to "off". 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
iotuneiotune element provides the
ability to provide additional per-device I/O tuning, with
values that can vary for each device (contrast this to
the <blkiotune>
element, 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 0.9.8
total_bytes_sectotal_bytes_sec element is the
total throughput limit in bytes per second. This cannot
appear with read_bytes_sec
or write_bytes_sec.read_bytes_secread_bytes_sec element is the
read throughput limit in bytes per second.write_bytes_secwrite_bytes_sec element is the
write throughput limit in bytes per second.total_iops_sectotal_iops_sec element is the
total I/O operations per second. This cannot
appear with read_iops_sec
or write_iops_sec.read_iops_secread_iops_sec element is the
read I/O operations per second.write_iops_secwrite_iops_sec element is the
write I/O operations per second.total_bytes_sec_maxtotal_bytes_sec_max element is the
maximum total throughput limit in bytes per second. This cannot
appear with read_bytes_sec_max
or write_bytes_sec_max.read_bytes_sec_maxread_bytes_sec_max element is the
maximum read throughput limit in bytes per second.write_bytes_sec_maxwrite_bytes_sec_max element is the
maximum write throughput limit in bytes per second.total_iops_sec_maxtotal_iops_sec_max element is the
maximum total I/O operations per second. This cannot
appear with read_iops_sec_max
or write_iops_sec_max.read_iops_sec_maxread_iops_sec_max element is the
maximum read I/O operations per second.write_iops_sec_maxwrite_iops_sec_max element is the
maximum write I/O operations per second.size_iops_secsize_iops_sec element is the
size of I/O operations per second.drivername attribute selects the primary
backend driver name, while the optional type
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".
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 0.9.7
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 setting of error_policy is "report".
There is also an
optional rerror_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 the error_policy for
read errors. Also note that "enospace" is not a valid
policy for read errors, so if error_policy is
set to "enospace" and no rerror_policy is
given, the read error policy will be left at its default,
which is "report".
io attribute controls specific
policies on I/O; qemu guests support "threads" and
"native". Since 0.8.8
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.
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.
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)
discard attribute controls whether
to discard (also known as "trim" or "unmap") requests 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)
iothread attribute assigns the
disk to an IOThread as defined by the range for the domain
iothreads
value. Multiple devices may be assigned to the same IOThread and
are numbered from 1 to the domain iothreads value.
Since 1.2.8 (QEMU only)
backenddomainbackenddomain element allows specifying a
backend domain (aka driver domain) hosting the disk. Use the
name attribute to specify the backend domain name.
Since 1.2.13 (Xen only)
bootorder
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
encryptionreadonlydevice='cdrom'.
shareabletransientserial<serial>WD-WMAP9A966149</serial>.
Since 0.7.1
wwnvendorproductaddressaddress 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 explicitly specified).
The type attribute is mandatory, and is typically
"pci" or "drive". For a "pci" controller, additional
attributes for bus, slot,
and function must be present, as well as
optional domain and multifunction.
Multifunction defaults to 'off'; any other value requires
QEMU 0.1.3 and libvirt 0.9.7. For a
"drive" controller, additional attributes
controller, bus, target
(libvirt 0.9.11), and unit
are available, each defaulting to 0.
authauth element is supported for a disk
type "network" that is using a source
element with the protocol attributes "rbd" or "iscsi".
If present, the auth element provides the
authentication credentials needed to access the source. It
includes a mandatory attribute username, which
identifies the username to use during authentication, as well
as a sub-element secret with mandatory
attribute type, 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 a uuid attribute
with the UUID of the secret object or a usage
attribute matching the key that was specified in the
secret object. libvirt 0.9.7
geometrygeometry element provides the
ability to override geometry settings. This mostly useful for
S390 DASD-disks or older DOS-disks. 0.10.0
cylscyls attribute is the
number of cylinders. headsheads attribute is the
number of heads. secssecs attribute is the
number of sectors per track. transtrans attribute is the
BIOS-Translation-Modus (none, lba or auto)blockioblockio element allows
to override any of the block device properties listed below.
Since 0.10.2 (QEMU and KVM)
logical_block_sizephysical_block_sizeA 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'>
<driver type='path' wrpolicy='immediate'/>
<source dir='/export/to/guest'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
<filesystem type='file' accessmode='passthrough'>
<driver name='loop' type='raw'/>
<driver type='path' wrpolicy='immediate'/>
<source file='/export/to/guest.img'/>
<target dir='/import/from/host'/>
<readonly/>
</filesystem>
...
</devices>
...
filesystemtype specifies the type of the
source. The possible values are:
type='mount'type if one is not specified.
This mode also has an optional
sub-element driver, with an
attribute type='path'
or type='handle' (since
0.9.7). The driver block has an optional attribute
wrpolicy that further controls interaction with
the host page cache; omitting the attribute gives default behavior,
while the value immediate means that a host writeback
is immediately triggered for all pages touched during a guest file
write operation (since 0.9.10).
type='template'type='file'type='block'type='ram'usage
which gives the memory usage limit in KiB, unless units
are specified by the units attribute. Only used
by LXC driver.
(since 0.9.13)type='bind'accessmode
which specifies the security mode for accessing the source
(since 0.8.5). Currently this only works
with type='mount' for the QEMU/KVM driver. The possible
values are:
accessmode='passthrough'source is accessed with the permissions of the
user inside the guest. This is the default accessmode if
one is not specified.
More info
accessmode='mapped'source is accessed with the permissions of the
hypervisor (QEMU process).
More info
accessmode='squash'drivertype attribute selects the primary
backend driver name, while the format
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. Parallels driver supports
a type of "ploop" with a format of "ploop".
sourcename attribute must be used with
type='template', and the dir attribute must
be used with type='mount'. The usage attribute
is used with type='ram' to set the memory limit in KiB,
unless units are specified by the units attribute.
targetsource 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.
readonlyspace_hard_limitspace_soft_limit
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:
type='pci'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), and function (a value
between 0 and 7, inclusive). Also available is
the multifunction 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.
type='drive'controller (a 2-digit controller
number), bus (a 2-digit bus number),
target (a 2-digit bus number),
and unit (a 2-digit unit number on the bus).
type='virtio-serial'controller (a 2-digit controller
number), bus (a 2-digit bus number),
and slot (a 2-digit slot within the bus).
type='ccid'bus (a 2-digit bus
number), and slot attribute (a 2-digit slot
within the bus). Since 0.8.8.
type='usb'bus (a hex value between 0 and 0xfff,
inclusive), and port (a dotted notation of up to
four octets, such as 1.2 or 2.1.3.1).
type='spapr-vio'reg (the hex value address
of the starting register). Since
0.9.9.
type='ccw'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) and
devno (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 1.0.4
type='isa'iobase and irq.
Since 1.2.1
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.
...
<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>
...
</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). The "virtio-serial"
controller has two additional optional
attributes ports and vectors, which
control how many devices can be connected through the
controller. A "scsi" controller has an optional
attribute model, which is one of "auto", "buslogic",
"ibmvscsi", "lsilogic", "lsisas1068", "lsisas1078", "virtio-scsi" or
"vmpvscsi". A "usb" controller has an optional attribute
model, which is one of "piix3-uhci", "piix4-uhci", "ehci",
"ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3", "vt82c686b-uhci",
"pci-ohci" or "nec-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. 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 given above.
An optional sub-element driver can specify the driver
specific options:
queuesqueues 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_luncmd_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_sectorsmax_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)
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.
...
<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 with
possible values pci-root, pcie-root,
pci-bridge, or dmi-to-pci-bridge.
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)
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. (pci-root and pci-bridge since 1.0.5)
...
<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) and can only be used to attach PCIe
devices. In order to connect standard PCI devices on a system
which has a pcie-root controller, a pci controller
with model='dmi-to-pci-bridge' is automatically
added. A dmi-to-pci-bridge controller plugs into a PCIe slot (as
provided by pcie-root), and itself provides 31 standard PCI
slots (which are not hot-pluggable). 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 devices with PCI addresses that are
auto-determined by libvirt will be placed on this pci-bridge
device. (since 1.1.2).
...
<devices>
<controller type='pci' index='0' model='pcie-root'/>
<controller type='pci' index='1' model='dmi-to-pci-bridge'>
<address type='pci' domain='0' bus='0' slot='0xe' function='0'/>
</controller>
<controller type='pci' index='2' model='pci-bridge'>
<address type='pci' domain='0' bus='1' slot='1' function='0'/>
</controller>
</devices>
...
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>
...
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>
<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 type='scsi' 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>
</source>
<address type='drive' controller='0' bus='0' target='0' unit='0'/>
</hostdev>
</devices>
...
hostdevhostdev element is the main container for describing
host devices. For each device, the mode is always
"subsystem" and the type is one of the following values
with additional attributes noted.
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.
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", follow the steps
described for a USB device to detach before starting the
guest or hot-plugging and reattach after stopping the guest
or hot-unplug.
sgio
(since 1.0.6) attribute indicates
whether the kernel will filter unprivileged SG_IO commands for
the disk, valid settings are "filtered" or "unfiltered".
The default is "filtered". The optional rawio
(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
disk section.
If a disk lun in the domain already has the rawio capability,
then this setting not required.
Note: The managed attribute is only used with PCI devices
and is ignored by all the other device types, thus setting
managed explicitly with other than PCI device has the same
effect as omitting it.
sourcevendor and product elements
or by the device's address on the host using the
address element.
Since 1.0.0, the source
element of USB devices may contain startupPolicy
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 |
address.
adapter
and address elements.
Since 1.2.8, the source
element of a SCSI device may contain the protocol
attribute. When the attribute is set to "iscsi", the host
device XML follows the network disk
device using the same name attribute and optionally
using the auth element to provide the authentication
credentials to the iSCSI server.
vendor, productvendor and product elements each have an
id 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.bootorder
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 for PCI devices,
Since 1.0.1 for USB devices.
romrom element is used to change how a PCI
device's ROM is presented to the guest. The optional 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"). Since
0.9.7 (QEMU and KVM only). 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, 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).
addressaddress element for USB devices has a
bus and device 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 the lspci or
with virsh
nodedev-list. See above for
more details on the address element.driverdriver
subelement that specifies which backend driver to use for PCI
device assignment. Use the name 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").
readonlyshareable
Note: Although shareable was introduced
in 1.0.6, it did not work as
as expected until 1.2.2.
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.
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>
...
hostdevhostdev element is the main container for describing
host devices. For block/character device passthrough mode is
always "capabilities" and type is "storage" for a block
device, "misc" for a character device and "net" for a host network
interface.
sourceUSB device redirection through a character device is supported since after 0.9.5 (KVM only):
...
<devices>
<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='2.00' allow='yes'/>
<usbdev allow='no'/>
</redirfilter>
</devices>
...
redirdevredirdev element is the main container for
describing redirected devices. bus must be "usb"
for a USB device.
An additional attribute type is required,
matching one of the
supported serial device types,
to describe the host side of the
tunnel; type='tcp'
or type='spicevmc' (which uses the usbredir
channel of a SPICE graphics
device) 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).
bootorder 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 1.0.1)
redirfilter 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 the vendor and product attributes.
version is the bcdDevice value of USB device, such as 1.00, 1.10 and 2.00.
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.
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.
mode='host'<address> sub-element.mode='host-certificates'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 the certutil command
when creating the certificates); if not present, it defaults to
/etc/pki/nssdb.mode='passthrough'type is required, matching one of the
supported serial device types, to
describe the host side of the tunnel; type='tcp'
or type='spicevmc' (which uses the smartcard
channel of a SPICE graphics
device) 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>, which fine-tunes the
correlation between the smartcard and a ccid bus
controller, documented above.
For now, qemu only supports at most one
smartcard, with an address of bus=0 slot=0.
...
<devices>
<interface type='direct' trustGuestRxFilters='yes'>
<source dev='eth0'/>
<mac address='52:54:00:5d:c7:9e'/>
<boot order='1'/>
<rom bar='off'/>
</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 above.
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.
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
an 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>
...
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 enslaved. 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 enslaved 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>
...
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.
...
<devices>
<interface type='user'/>
...
<interface type='user'>
<mac address="00:11:22:33:44:55"/>
</interface>
</devices>
...
Provides a means for the administrator to execute an arbitrary script to connect the guest's network to the LAN. The guest will have a tun device created with a name of vnetN, which can also be overridden with the <target> element. After creating the tun device a shell script will be run which is expected to do whatever host network integration is required. By default this script is called /etc/qemu-ifup but can be overridden.
...
<devices>
<interface type='ethernet'/>
...
<interface type='ethernet'>
<target dev='vnet7'/>
<script path='/etc/qemu-ifup-mynet'/>
</interface>
</devices>
...
Provides direct attachment of the virtual machine's NIC to the given
physical interface of the host.
Since 0.7.7 (QEMU and KVM only)
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.
vepabridgevepa mode,
a VEPA capable bridge is required.privateprivate mode.passthrough
...
<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.
manageridtypeidtypeidversioninstanceid
...
<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
...
<devices>
...
<interface type='direct'>
<source dev='eth0' mode='private'/>
<virtualport type='802.1Qbh'>
<parameters profileid='finance'/>
</virtualport>
</interface>
</devices>
...
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>
...
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>
...
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>
...
...
<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
...
<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'>
<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:
namename 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)
name 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)
txmodetxmode 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)ioeventfdevent_idxevent_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)queuesqueues attribute controls the number of
queues to be used for the
Multiqueue virtio-net feature. If the interface has <model
type='virtio'/>, multiple packet processing queues can be
created; each queue will potentially be handled by a different
processor, resulting in much higher throughput.
Since 1.0.6 (QEMU and KVM only)
host offloading optionscsum, gso, tso4,
tso6, ecn and ufo
attributes with possible values on
and off can be used to turn off host offloading options.
By default, the supported offloads are enabled by QEMU.
Since 1.2.9 (QEMU only)
The mrg_rxbuf attribute can be used to control
mergeable rx buffers on the host side. Possible values are
on (default) and off.
Since 1.2.13 (QEMU only)
guest offloading optionscsum, tso4,
tso6, ecn and ufo
attributes with possible values on
and off can be used to turn off guest offloading options.
By default, the supported offloads are enabled by QEMU.
Since 1.2.9 (QEMU only)
...
<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'/>
</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.
...
<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 must not start with either 'vnet' or 'vif', which are prefixes reserved by libvirt and certain hypervisors. Manually specified targets using these prefixes will 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>
...
...
<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
...
<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).
...
<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)
...
<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.
...
<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. (openvswitch
and type='hostdev' SR-IOV interfaces do support transparent vlan
tagging of guest traffic; everything else, 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 specific vlans.) To allow for specification of multiple
tags (in the case of vlan trunking), a
subelement, <tag>, specifies which vlan tag
to use (for example: <tag id='42'/>. If an
interface has more than one <vlan> element
defined, it is assumed that the user wants to do VLAN trunking
using all the specified tags. In the case that vlan trunking
with a single tag is desired, the optional
attribute trunk='yes' can be added to the toplevel
vlan element.
For network connections using openvswitch it is possible to
configure the 'native-tagged' and 'native-untagged' vlan modes
Since 1.1.0. This uses the optional
nativeMode attribute on the <tag>
element: nativeMode may be set to 'tagged' or
'untagged'. The id attribute of the element sets the native vlan.
...
<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
...
<devices>
<interface type='network'>
<source network='default'/>
<target dev='vnet0'/>
<ip address='192.168.122.5' prefix='24'/>
<route family='ipv4' address='192.168.122.0' prefix='24' via='192.168.122.1'/>
<route family='ipv4' via='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' via='192.168.122.1'/>
<route family='ipv4' via='192.168.122.1'/>
</hostdev>
</devices>
...
Since 1.2.12 the network devices and host devices
with network capabilities can be provided zero or more IP addresses to set
on the target device. 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, the
address attribute holds the IP address. The prefix
is not mandatory since some hypervisors do not handle it.
Since 1.2.12 route elements can also be added
to define the network routes to use for the network device. The attributes
of this element are described in the documentation for the route
element in network definitions.
This is only used by the LXC driver.
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/vhost.sock' mode='server'/>
<model type='virtio'/>
</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.
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'/>
</devices>
...
inputinput element has one mandatory attribute,
the type whose value can be 'mouse', 'tablet' or
(since 1.2.2) 'keyboard'.
The tablet provides absolute cursor movement,
while the mouse uses relative movement. The optional
bus attribute can be used to refine the exact device type.
It takes values "xen" (paravirtualized), "ps2" and "usb".
The input element has an optional
sub-element <address> which can tie the
device to a particular PCI
slot, documented above.
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>
...
hubhub element has one mandatory attribute,
the type whose value can only be 'usb'.
The hub element has an optional
sub-element <address>
with type='usb'which can tie the device to a
particular controller, documented
above.
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>
...
graphicsgraphics element has a mandatory type
attribute which takes the value "sdl", "vnc", "rdp" or "desktop":
"sdl"display attribute for
the display to use, an xauth attribute for
the authentication identifier, and an
optional fullscreen attribute accepting
values 'yes' or 'no'.
"vnc"port attribute
specifies the TCP port number (with -1 as legacy syntax
indicating that it should be
auto-allocated). The autoport attribute is
the new preferred syntax for indicating autoallocation of
the TCP port to use. The listen attribute is
an IP address for the server to listen
on. The passwd attribute provides a VNC
password in clear text. The keymap attribute
specifies the keymap to use. It is possible to set a limit
on the validity of the password be giving an
timestamp passwdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. The connected attribute
allows control of connected client during password changes.
VNC accepts keep value only.
since 0.9.3
NB, this may not be supported by all hypervisors.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. 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 and autoport
having no effect due to security reasons).
Since 1.0.6
"spice"
Starts a SPICE server. The port attribute
specifies the TCP port number (with -1 as legacy syntax
indicating that it should be auto-allocated),
while tlsPort gives an alternative secure
port number. The autoport attribute is the
new preferred syntax for indicating autoallocation of
needed port numbers. The listen attribute is
an IP address for the server to listen
on. The passwd attribute provides a SPICE
password in clear text. The keymap
attribute specifies the keymap to use. It is possible to
set a limit on the validity of the password be giving an
timestamp passwdValidTo='2010-04-09T15:51:00'
assumed to be in UTC. The connected attribute
allows control of connected client during password changes.
SPICE accepts keep to keep client connected,
disconnect to disconnect client and
fail to fail changing password.
Since 0.9.3
NB, this may not be supported by all hypervisors.
"spice" since 0.8.6.
The defaultMode attribute sets the default channel
security policy, valid values are secure,
insecure and the default any
(which is secure if possible, but falls back to insecure
rather than erroring out if no secure path is
available). "defaultMode" since
0.9.12.
When 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 the mode
attribute to either secure or insecure.
Setting the mode attribute overrides the default value as set
by the defaultMode attribute. (Note that specifying
any as mode discards the entry as the channel would
inherit the default mode anyways)
Valid channel names
include main, display,
inputs, cursor,
playback, record
(all since 0.8.6);
smartcard (since
0.8.8); and usbredir
(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'/>
</graphics>
Spice supports variable compression settings for audio,
images and streaming, since
0.9.1. These settings are accessible via
the compression attribute in all following
elements: image to set image compression
(accepts auto_glz, auto_lz,
quic, glz, lz,
off), jpeg for JPEG
compression for images over wan
(accepts auto, never,
always), zlib for configuring
wan image compression (accepts auto,
never, always)
and playback for enabling audio stream
compression (accepts on or off).
Streaming mode is set by the streaming
element, settings its mode attribute to one
of filter, all
or off, since 0.9.2.
Copy & Paste functionality (via Spice agent) is set
by the clipboard element. It is enabled by
default, and can be disabled by setting
the copypaste property
to no, since
0.9.3.
Mouse mode is set by the mouse element,
setting its mode attribute to one of
server or client ,
since 0.9.11. If no mode is
specified, the qemu default will be used (client mode).
File transfer functionality (via Spice agent) is set using the
filetransfer element.
It is enabled by default, and can be disabled by setting the
enable property to no ,
since since 1.2.2.
"rdp"port attribute
specifies the TCP port number (with -1 as legacy syntax
indicating that it should be
auto-allocated). The autoport attribute is
the new preferred syntax for indicating autoallocation of
the TCP port to use. The replaceUser
attribute is a boolean deciding whether multiple
simultaneous connections to the VM are permitted.
The multiUser 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"display
and fullscreen.
Rather than putting the address information used to set up the
listening socket for graphics types vnc
and spice in
the <graphics> listen attribute,
a separate subelement of <graphics>,
called <listen> can be specified (see the
examples above)since
0.9.4. <listen> accepts the following
attributes:
typeaddress
or network. This tells whether this listen
element is specifying the address to be used directly, or by
naming a network (which will then be used to determine an
appropriate address for listening).
addresstype='address', the address
attribute will contain either an IP address or hostname (which
will be resolved to an IP address via a DNS query) to listen
on. In the "live" XML of a running domain, this attribute will
be set to the IP address used for listening, even
if type='network'.
networktype='network', the network
attribute will contain the name of a network in libvirt's list
of configured networks. The named network configuration will
be examined to determine an appropriate listen address. For
example, if the network has an IPv4 address in its
configuration (e.g. if it has a forward type
of route, 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.
A video device.
...
<devices>
<video>
<model type='vga' vram='16384' heads='1'>
<acceleration accel3d='yes' accel2d='yes'/>
</model>
</video>
</devices>
...
video
The video element is the container for describing
video devices. For backwards compatibility, if no video
is set but there is a graphics in domain xml, then
libvirt will add a default video according to the guest
type.
For a guest of type "kvm", the default video is:
type with value "cirrus", vram with value
"16384" and heads with value "1". By default, the first
video device in domain xml is the primary one, but the optional
attribute primary (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".
model
The model element has a mandatory type
attribute which takes the value "vga", "cirrus", "vmvga", "xen",
"vbox", or "qxl" (since 0.8.6) depending
on the hypervisor features available.
You can provide the amount of video memory in kibibytes (blocks of
1024 bytes) using vram. This is supported only for guest
type of "libxl", "parallels", "qemu", "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 "parallels", "kvm", "vbox" and "vmx".
For guest type of kvm the optional attribute ram
(since 1.0.2) is allowed for "qxl" type
only and specifies the size of the primary bar, while the optional
attribute vram specifies the secondary bar size.
If "ram" or "vram" are not supplied a default value is used. The ram
should also be rounded to power of two as vram. There is also optional
attribute vgamem (since 1.2.11 (QEMU
only)) to set the size of VGA framebuffer for fallback mode of
QXL device.
accelerationaccel3d and accel2d attributes in the
acceleration element.
addressaddress sub-element can be used to
tie the video device to a particular PCI slot.
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'>
<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.
Each character device element has an optional
sub-element <address> which can tie the
device to a
particular controller or PCI
slot.
A character device presents itself to the guest as one of the following types.
...
<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.
...
<devices>
<serial type='pty'>
<source path='/dev/pts/3'/>
<target port='0'/>
</serial>
</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 serial ports. There is also an optional
type attribute since 1.0.2
which has two choices for its value, one is isa-serial,
the other is usb-serial. If type is missing,
isa-serial will be used by default. For usb-serial
an optional sub-element <address> with
type='usb' can tie the device to a particular controller,
documented above.
The console element is used to represent interactive consoles. Depending on the type of guest in use, the consoles might be paravirtualized devices, or they might be a clone of a serial device, according to the following rules:
targetType attribute is set, then the default
device type is according to the hypervisor's rules. The default
type will be added when re-querying the XML fed into libvirt.
For fully virtualized guests, the default device type will usually
be a serial port.targetType attribute is serial,
then if no <serial> element exists, the console
element will be copied to the serial element. If a <serial>
element does already exist, the console element will be ignored.targetType attribute is not serial,
it will be treated normally.console element may use a targetType
of serial. Secondary consoles must all be paravirtualized.
console element may use a
targetType of sclp or sclplm
(line mode). SCLP is the native console type for s390. There's no
controller associated to SCLP consoles.
Since 1.0.2
A virtio console device is exposed in the guest as /dev/hvc[0-7] (for more information, see http://fedoraproject.org/wiki/Features/VirtioSerial) Since 0.8.3
...
<devices>
<console type='pty'>
<source path='/dev/pts/4'/>
<target port='0'/>
</console>
<!-- KVM virtio console -->
<console type='pty'>
<source path='/dev/pts/5'/>
<target type='virtio' port='0'/>
</console>
</devices>
...
...
<devices>
<!-- KVM s390 sclp console -->
<console type='pty'>
<source path='/dev/pts/1'/>
<target type='sclp' port='0'/>
</console>
</devices>
...
If the console is presented as a serial port, the target
element has the same attributes as for a serial port. There is usually
only 1 console.
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.
guestfwdtarget
element must have address and port attributes.
Since 0.7.3virtioname is specified,
/dev/virtio-ports/$name (for more info, please see
http://fedoraproject.org/wiki/Features/VirtioSerial). The
optional element address can tie the channel to a
particular type='virtio-serial'
controller, documented above.
With qemu, if name 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 optional
state attribute that reflects whether a process in the
guest is active on the channel. This is an output-only attribute.
Possible values for the state attribute are
connected and disconnected.
spicevmcmain channel. The target
element must be present, with
attribute type='virtio'; an optional
attribute name controls how the guest will have
access to the channel, and defaults
to name='com.redhat.spice.0'. The
optional address element can tie the channel to a
particular type='virtio-serial' controller.
Since 0.8.8A character device presents itself to the host as one of the following types.
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>
...
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>
...
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>
...
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>
...
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.
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>
...
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>
...
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. Since 0.8.5
you can also use telnets
(secure telnet) and tls.
...
<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>
...
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>
...
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>
...
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.
...
<devices>
<serial type="spiceport">
<source channel="org.qemu.console.serial.0"/>
<target port="1"/>
</serial>
</devices>
...
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:
masterslave
A virtual sound card can be attached to the host via the
sound element. Since 0.4.3
...
<devices>
<sound model='es1370'/>
</devices>
...
soundsound 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 'es1370', 'sb16', 'ac97', 'ich6' and 'usb'.
(
'ac97' only since 0.6.0, 'ich6' only since 0.8.8,
'usb' only since 1.2.7)
Since 0.9.13, a sound element
with ich6 model 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) and 'micro'
(advertise a speaker and a microphone).
...
<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, documented above.
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:
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:
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.
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'/>
</memballoon>
</devices>
</domain>
model
The required model attribute specifies what type
of balloon device is provided. Valid values are specific to
the virtualization platform
period
The optional period allows the QEMU virtio memory
balloon driver to provide statistics through the virsh
dommemstat [domain] command. By default, collection is
not enabled. In order to enable, use the virsh dommemstat
[domain] --period [number] command or virsh edit
command to add the option to the XML definition.
The virsh 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.
Since 1.1.1, requires QEMU 1.5
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>
</rng>
</devices>
...
model
The required model attribute specifies what type
of RNG device is provided. Valid values are specific to
the virtualization platform:
rate
The optional rate element allows limiting the rate at
which entropy can be consumed from the source. The mandatory
attribute bytes specifies how many bytes are permitted
to be consumed per period. An optional period attribute
specifies the duration of a period in milliseconds; if omitted, the
period is taken as 1000 milliseconds (1 second).
Since 1.0.4
backend
The backend element specifies the source of entropy
to be used for the domain. The source model is configured using the
model attribute. Supported source models are:
backend model='random'
This backend type expects a non-blocking character device as input.
The only accepted paths are /dev/random and /dev/hwrng. The file
name is specified as contents of the backend element.
When no file name is specified the hypervisor default is used.
backend model='egd'This backend connects to a source using the EGD protocol. The source is specified as a character device. Refer to character device host interface for more information.
The TPM device enables a QEMU guest to have access to TPM functionality.
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>
...
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.
backend
The backend element specifies the type of
TPM device. The following types are supported:
backend type='passthrough'
This backend type requires exclusive access to a TPM device on
the host.
An example for such a device is /dev/tpm0. The filename is
specified as path attribute of the source element.
If no file name is specified then /dev/tpm0 is automatically used.
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='0x3000'/>
</nvram>
</devices>
...
spapr-vioVIO device address type, only valid for PPC64.
regDevice address
panic device enables libvirt to receive panic notification from a QEMU guest. Since 1.2.1, QEMU and KVM only
Example: usage of panic configuration
...
<devices>
<panic>
<address type='isa' iobase='0x505'/>
</panic>
</devices>
...
addressaddress of panic. The default ioport is 0x505. Most users don't need to specify an address.
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'>
<size unit='M'>4</size>
</shmem>
<shmem name='shmem_server'>
<size unit='M'>2</size>
<server path='/tmp/socket-shmem'/>
<msi vectors='32' ioeventfd='on'/>
</shmem>
</devices>
...
shmemshmem element has one mandatory attribute,
name to identify the shared memory.
sizesize element specifies the size of the shared
memory. This must be power of 2 and greater than or equal to 1 MiB.
serverserver element can be used to configure a server
socket the device is supposed to connect to. The optional
path attribute specifies the path to the unix socket and
defaults to /var/lib/libvirt/shmem/$shmem-$name-sock.
msimsi element enables/disables (values "on"/"off",
respectively) MSI interrupts. This option can currently be used only
together with the server element. The vectors
attribute can be used to specify the number of interrupt
vectors. The ioeventd attribute enables/disables (values
"on"/"off", respectively) ioeventfd.
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
typestatic, dynamic or none
to determine whether libvirt automatically generates a unique security
label or not.
modelrelabelyes or no. This must always
be yes if dynamic label assignment is used. With
static label assignment it will default to no.
labelbaselabeltype 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 of my_svirt_t
as the value for the type field.)
imagelabelWhen 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.
Example configurations for each driver are provide on the driver specific pages listed below