Node devices XML format

Node Device XML

There are several libvirt functions, all with the prefix virNodeDevice, which deal with management of host devices that can be handed to guests via passthrough as <hostdev> elements in the domain XML. These devices are represented as a hierarchy, where a device on a bus has a parent of the bus controller device; the root of the hierarchy is the node named "computer".

When represented in XML, a node device uses the top-level device element, with the following elements present according to the type of device:

name

The name for this device. The name will be alphanumeric, with words separated by underscore. For many devices, the name is just the bus type and address, as in "pci_0000_00_02_1" or "usb_1_5_3", but some devices are able to provide more specific names, such as "net_eth1_00_27_13_6a_fe_00". This is a read-only field that is reported by the device driver. If this element is set when defining a new device, it will be ignored.

path

Fully qualified sysfs path to the device. This is a read-only field that is reported by the device driver. If this element is set when defining a new device, it will be ignored.

parent

This element identifies the parent node in the device hierarchy. The value of the element will correspond with the device parent's name element or computer if the device does not have any parent.

driver

This elements reports the driver in use for this device. The presence of this element in the output XML depends on whether the underlying device manager (most likely udev) exposes information about the driver.

devnode

This node appears for each associated /dev special file. A mandatory attribute type specify the kind of file path, which may be either dev for the main name, or link for additional symlinks.

capability

This node appears for each capability that libvirt associates with a node. A mandatory attribute type lists which category the device belongs to, and controls which further subelements will be present to describe the node:

system

Describes the overall host. Sub-elements include:

product: If present, a simple text string giving the product name of the system.
hardware: Describes the hardware of the system, including sub-elements for vendor, version, serial, and uuid.
firmware: Describes the firmware of the system, including sub-elements for vendor, version, and release_date.

pci

Describes a device on the host's PCI bus. Sub-elements include:

class

Optional element for combined class, subclass and programming interface codes as 6-digit hexadecimal number. Since 5.2.0

domain

Which domain the device belongs to.

bus

Which bus within the domain.

slot

Which slot within the bus.

function

Which function within the slot.

product

Product details from the device ROM, including an attribute id with the hexadecimal product id, and an optional text description of that id.

vendor

Vendor details from the device ROM, including an attribute id with the hexadecimal vendor id, and an optional text name of that vendor.

iommuGroup

This optional element describes the "IOMMU group" this device belongs to. If the element exists, it has a mandatory number attribute which tells the group number used for management of the group (all devices in group "n" will be found in "/sys/kernel/iommu_groups/n"). It will also have a list of address subelements, each containing the PCI address of a device in the same group. The toplevel device will itself be included in this list.

capability

This optional element can occur multiple times. If it exists, it has a mandatory type attribute which will be set to:

phys_function

That means there will be a single address subelement which contains the PCI address of the SRIOV Physical Function (PF) that is the parent of this device (and this device is, by implication, an SRIOV Virtual Function (VF)).

virt_functions

In this case this device is an SRIOV PF, and the capability element will have a list of address subelements, one for each VF on this PF. If the host system supports reporting it (via the "sriov_totalvfs" file in the device's sysfs directory) the capability element will also have an attribute named maxCount which is the maximum number of SRIOV VFs supported by this device, which could be higher than the number of VFs that are curently active since 1.3.0; in this case, even if there are currently no active VFs the virtual_functions capabililty will still be shown.

pci-bridge or cardbus-bridge

This shows merely that the lower 7 bits of PCI header type have either value of 1 or 2 respectively. Usually this means such device cannot be used for PCI passthrough. Since 1.3.3

mdev_types

This device is capable of creating mediated devices, and the capability will contain a list of type elements, which list all mdev types supported on the physical device. Since 3.4.0 Each type element has a single id attribute that holds an official vendor-supplied identifier for the type. It supports the following sub-elements:

name: The name element holds a vendor-supplied code name for the given mediated device type. This is an optional element.
deviceAPI: The value of this element describes how an instance of the given type will be presented to the guest by the VFIO framework.
availableInstances: This element reports the current state of resource allocation. In other words, how many instances of the given type can still be successfully created on the physical device.

numa

This optional element contains information on the PCI device with respect to NUMA. For example, the optional node attribute tells which NUMA node is the PCI device associated with.

pci-express

This optional element contains information on PCI Express part of the device. For example, it can contain a child element link which addresses the PCI Express device's link. While a device has its own capabilities (validity='cap'), the actual run time capabilities are negotiated on the device initialization (validity='sta'). The link element then contains three attributes: port which says in which port is the device plugged in, speed (in GigaTransfers per second) and width for the number of lanes used. Since the port can't be negotiated, it's not exposed in ./pci-express/link/[@validity='sta'].

usb_device

Describes a device on the host's USB bus, based on its location within the bus. Sub-elements include:

bus: Which bus the device belongs to.
device: Which device within the bus.
product: Product details from the device ROM, including an attribute id with the hexadecimal product id, and an optional text description of that id.
vendor: Vendor details from the device ROM, including an attribute id with the hexadecimal vendor id, and an optional text name of that vendor.

usb

Describes a USB device, based on its advertised driver interface. Sub-elements include:

number: The device number.
class: The device class.
subclass: The device subclass.
protocol: The device protocol.
description: If present, a description of the device.

net

Describes a device capable for use as a network interface. Sub-elements include:

interface

The interface name tied to this device.

address

If present, the MAC address of the device.

link

Optional to reflect the status of the link. It has two optional attributes: speed in Mbits per second and state to tell the state of the link. So far, the whole element is just for output, not setting.

feature

If present, the hw offloads supported by this network interface. Possible features are:

rx: rx-checksumming
tx: tx-checksumming
sg: scatter-gather
tso: tcp-segmentation-offload
ufo: udp-fragmentation-offload
gso: generic-segmentation-offload
gro: generic-receive-offload
lro: large-receive-offload
rxvlan: rx-vlan-offload
txvlan: tx-vlan-offload
ntuple: ntuple-filters
rxhash: receive-hashing
rdma: remote-direct-memory-access
txudptnl: tx-udp-tunnel-segmentation
switchdev: kernel-forward-plane-offload

capability

A network protocol exposed by the device, where the attribute type can be "80203" for IEEE 802.3, or "80211" for various flavors of IEEE 802.11.

scsi_host

Describes a SCSI host device. Sub-elements include:

host: The SCSI host number.
unique_id: On input, this optionally provides the value from the 'unique_id' file found in the scsi_host's directory. To view the values of all 'unique_id' files, use find -H /sys/class/scsi_host/host{0..9}/unique_id | xargs grep '[0-9]'. On output, if the unique_id file exists, the value from the file will be displayed. This can be used in order to help uniquely identify the scsi_host adapter in a Storage Pool. Since 1.2.7
capability: Current capabilities include "vports_ops" (indicates vport operations are supported) and "fc_host". "vport_ops" could contain two optional sub-elements: vports, and max_vports. vports shows the number of vport in use. max_vports shows the maximum vports the HBA supports. "fc_host" implies following sub-elements: wwnn, wwpn, and optionally fabric_wwn.

scsi

Describes a SCSI device. Sub-elements include:

host: The SCSI host containing the device.
bus: The bus within the host.
target: The target within the bus.
lun: The lun within the target.
type: The type of SCSI device.

storage

Describes a device usable for storage. Sub-elements include:

block: A block device file name that accesses the storage present on the device.
bus: If present, the name of the bus the device is found on.
drive_type: The type of the drive, such as "disk" or "cdrom".
model: Any model information available from the device.
vendor: Any vendor information available from the device.
serial: Any serial number information available from the device.
size: For fixed-size storage, the amount of storage available.
capability: If present, an additional capability is listed via the attribute type. Current capabilities include "hotpluggable" and "removable", with the latter implying the following sub-elements: media_available (0 or 1), media_size, and media_label.

drm

Describes a Direct Rendering Manager (DRM) device. Sub-elements include:

type: The type of DRM device. Could be primary, control or render.

mdev

Describes a mediated device. Since 3.4.0 Sub-elements include:

type: Describes a mediated device type which acts as an abstract template defining a resource allocation for instances of this device type. The element has one attribute id which holds an official vendor-supplied identifier for the type.
iommuGroup: This element supports a single attribute number which holds the IOMMU group number to which the mediated device belongs. This is a read-only field that is reported by the device driver.
attr: This optional element can occur multiple times. It represents a vendor-specific attribute that is used to configure this mediated device. It has two required attributes: name and value.

ccw

Describes a Command Channel Word (CCW) device commonly found on the S390 architecture. Sub-elements include:

cssid: The channel subsystem identifier.
ssid: The subchannel-set identifier.
devno: The device number.

css

Describes a Channel SubSystem (CSS) device commonly found on the S390 architecture. Sub-elements include:

cssid: The channel subsystem identifier.
ssid: The subchannel-set identifier.
devno: The device number.

Examples

The following are some example node device XML outputs:

<device>
  <name>computer</name>
  <capability type='system'>
    <product>2241B36</product>
    <hardware>
      <vendor>LENOVO</vendor>
      <version>ThinkPad T500</version>
      <serial>R89055N</serial>
      <uuid>c9488981-5049-11cb-9c1c-993d0230b4cd</uuid>
    </hardware>
    <firmware>
      <vendor>LENOVO</vendor>
      <version>6FET82WW (3.12 )</version>
      <release_date>11/26/2009</release_date>
    </firmware>
  </capability>
</device>

<device>
  <name>net_eth1_00_27_13_6a_fe_00</name>
  <parent>pci_0000_00_19_0</parent>
  <capability type='net'>
    <interface>eth1</interface>
    <address>00:27:13:6a:fe:00</address>
    <capability type='80203'/>
  </capability>
</device>

<device>
  <name>pci_0000_02_00_0</name>
  <path>/sys/devices/pci0000:00/0000:00:04.0/0000:02:00.0</path>
  <parent>pci_0000_00_04_0</parent>
  <driver>
    <name>igb</name>
  </driver>
  <capability type='pci'>
    <class>0x020000</class>
    <domain>0</domain>
    <bus>2</bus>
    <slot>0</slot>
    <function>0</function>
    <product id='0x10c9'>82576 Gigabit Network Connection</product>
    <vendor id='0x8086'>Intel Corporation</vendor>
    <capability type='virt_functions'>
      <address domain='0x0000' bus='0x02' slot='0x10' function='0x0'/>
      <address domain='0x0000' bus='0x02' slot='0x10' function='0x2'/>
      <address domain='0x0000' bus='0x02' slot='0x10' function='0x4'/>
      <address domain='0x0000' bus='0x02' slot='0x10' function='0x6'/>
      <address domain='0x0000' bus='0x02' slot='0x11' function='0x0'/>
      <address domain='0x0000' bus='0x02' slot='0x11' function='0x2'/>
      <address domain='0x0000' bus='0x02' slot='0x11' function='0x4'/>
    </capability>
    <iommuGroup number='12'>
      <address domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
      <address domain='0x0000' bus='0x02' slot='0x00' function='0x1'/>
    </iommuGroup>
    <pci-express>
      <link validity='cap' port='1' speed='2.5' width='1'/>
      <link validity='sta' speed='2.5' width='1'/>
    </pci-express>
  </capability>
</device>