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eba98a1db9
Add up-to-date information about creating and defining mediated devices in libvirt. Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
315 lines
12 KiB
XML
315 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Host device management</h1>
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<p>
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Libvirt provides management of both physical and virtual host devices
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(historically also referred to as node devices) like USB, PCI, SCSI, and
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network devices. This also includes various virtualization capabilities
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which the aforementioned devices provide for utilization, for example
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SR-IOV, NPIV, MDEV, DRM, etc.
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</p>
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<p>
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The node device driver provides means to list and show details about host
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devices (<code>virsh nodedev-list</code>, <code>virsh nodedev-info</code>,
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and <code>virsh nodedev-dumpxml</code>), which are generic and can be used
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with all devices. It also provides the means to manage virtual devices.
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Persistently-defined virtual devices are only supported for mediated
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devices, while transient devices are supported by both mediated devices
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and NPIV (<a href="https://wiki.libvirt.org/page/NPIV_in_libvirt">more
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info about NPIV)</a>).
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</p>
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<p>
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Persistent virtual devices are managed with
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<code>virsh nodedev-define</code> and <code>virsh nodedev-undefine</code>.
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Persistent devices can be configured to start manually or automatically
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using <code>virsh nodedev-autostart</code>. Inactive devices can be made
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active with <code>virsh nodedev-start</code>.
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</p>
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<p>
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Transient virtual devices are started and stopped with the commands
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<code>virsh nodedev-create</code> and <code>virsh nodedev-destroy</code>.
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</p>
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<p>
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Devices on the host system are arranged in a tree-like hierarchy, with
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the root node being called <code>computer</code>. The node device driver
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supports udev backend (HAL backend was removed in <code>6.8.0</code>).
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</p>
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<p>
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Details of the XML format of a host device can be found <a
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href="formatnode.html">here</a>. Of particular interest is the
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<code>capability</code> element, which describes features supported by
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the device. Some specific device types are addressed in more detail
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below.
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</p>
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<h2>Basic structure of a node device</h2>
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<pre>
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<device>
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<name>pci_0000_00_17_0</name>
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<path>/sys/devices/pci0000:00/0000:00:17.0</path>
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<parent>computer</parent>
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<driver>
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<name>ahci</name>
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</driver>
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<capability type='pci'>
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...
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</capability>
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</device></pre>
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<ul id="toc"/>
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<h2><a id="PCI">PCI host devices</a></h2>
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<dl>
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<dt><code>capability</code></dt>
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<dd>
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When used as top level element, the supported values for the
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<code>type</code> attribute are <code>pci</code> and
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<code>phys_function</code> (see <a href="#SRIOVCap">SR-IOV below</a>).
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</dd>
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</dl>
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<pre>
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<device>
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<name>pci_0000_04_00_1</name>
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<path>/sys/devices/pci0000:00/0000:00:06.0/0000:04:00.1</path>
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<parent>pci_0000_00_06_0</parent>
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<driver>
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<name>igb</name>
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</driver>
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<capability type='pci'>
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<domain>0</domain>
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<bus>4</bus>
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<slot>0</slot>
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<function>1</function>
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<product id='0x10c9'>82576 Gigabit Network Connection</product>
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<vendor id='0x8086'>Intel Corporation</vendor>
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<iommuGroup number='15'>
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<address domain='0x0000' bus='0x04' slot='0x00' function='0x1'/>
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</iommuGroup>
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<numa node='0'/>
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<pci-express>
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<link validity='cap' port='1' speed='2.5' width='2'/>
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<link validity='sta' speed='2.5' width='2'/>
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</pci-express>
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</capability>
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</device></pre>
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<p>
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The XML format for a PCI device stays the same for any further
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capabilities it supports, a single nested <code><capability></code>
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element will be included for each capability the device supports.
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</p>
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<h3><a id="SRIOVCap">SR-IOV capability</a></h3>
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<p>
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Single root input/output virtualization (SR-IOV) allows sharing of the
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PCIe resources by multiple virtual environments. That is achieved by
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slicing up a single full-featured physical resource called physical
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function (PF) into multiple devices called virtual functions (VFs) sharing
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their configuration with the underlying PF. Despite the SR-IOV
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specification, the amount of VFs that can be created on a PF varies among
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manufacturers.
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</p>
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<p>
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Suppose the NIC <a href="#PCI">above</a> was also SR-IOV capable, it would
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also include a nested
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<code><capability></code> element enumerating all virtual
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functions available on the physical device (physical port) like in the
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example below.
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</p>
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<pre>
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<capability type='pci'>
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...
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<capability type='virt_functions' maxCount='7'>
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<address domain='0x0000' bus='0x04' slot='0x10' function='0x1'/>
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<address domain='0x0000' bus='0x04' slot='0x10' function='0x3'/>
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<address domain='0x0000' bus='0x04' slot='0x10' function='0x5'/>
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<address domain='0x0000' bus='0x04' slot='0x10' function='0x7'/>
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<address domain='0x0000' bus='0x04' slot='0x11' function='0x1'/>
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<address domain='0x0000' bus='0x04' slot='0x11' function='0x3'/>
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<address domain='0x0000' bus='0x04' slot='0x11' function='0x5'/>
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</capability>
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...
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</capability></pre>
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<p>
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A SR-IOV child device on the other hand, would then report its top level
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capability type as a <code>phys_function</code> instead:
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</p>
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<pre>
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<device>
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...
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<capability type='phys_function'>
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<address domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
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</capability>
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...
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</device></pre>
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<h3><a id="MDEVCap">MDEV capability</a></h3>
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<p>
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A device capable of creating mediated devices will include a nested
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capability <code>mdev_types</code> which enumerates all supported mdev
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types on the physical device, along with the type attributes available
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through sysfs. A detailed description of the XML format for the
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<code>mdev_types</code> capability can be found
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<a href="formatnode.html#MDEVTypesCap">here</a>.
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</p>
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<p>
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The following example shows how we might represent an NVIDIA GPU device
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that supports mediated devices. See below for <a href="#MDEV">more
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information about mediated devices</a>.
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</p>
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<pre>
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<device>
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...
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<driver>
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<name>nvidia</name>
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</driver>
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<capability type='pci'>
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...
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<capability type='mdev_types'>
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<type id='nvidia-11'>
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<name>GRID M60-0B</name>
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<deviceAPI>vfio-pci</deviceAPI>
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<availableInstances>16</availableInstances>
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</type>
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<!-- Here would come the rest of the available mdev types -->
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</capability>
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...
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</capability>
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</device></pre>
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<h2><a id="MDEV">Mediated devices (MDEVs)</a></h2>
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<p>
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Mediated devices (<span class="since">Since 3.2.0</span>) are software
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devices defining resource allocation on the backing physical device which
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in turn allows the parent physical device's resources to be divided into
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several mediated devices, thus sharing the physical device's performance
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among multiple guests. Unlike SR-IOV however, where a PCIe device appears
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as multiple separate PCIe devices on the host's PCI bus, mediated devices
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only appear on the mdev virtual bus. Therefore, no detach/reattach
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procedure from/to the host driver procedure is involved even though
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mediated devices are used in a direct device assignment manner. A
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detailed description of the XML format for the <code>mdev</code>
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capability can be found <a href="formatnode.html#mdev">here</a>.
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</p>
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<h3>Example of a mediated device</h3>
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<pre>
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<device>
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<name>mdev_4b20d080_1b54_4048_85b3_a6a62d165c01</name>
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<path>/sys/devices/pci0000:00/0000:00:02.0/4b20d080-1b54-4048-85b3-a6a62d165c01</path>
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<parent>pci_0000_06_00_0</parent>
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<driver>
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<name>vfio_mdev</name>
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</driver>
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<capability type='mdev'>
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<type id='nvidia-11'/>
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<uuid>4b20d080-1b54-4048-85b3-a6a62d165c01</uuid>
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<iommuGroup number='12'/>
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</capability>
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</device></pre>
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<p>
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The support of mediated device's framework in libvirt's node device driver
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covers the following features:
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</p>
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<ul>
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<li>
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list available mediated devices on the host
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(<span class="since">Since 3.4.0</span>)
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</li>
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<li>
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display device details
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(<span class="since">Since 3.4.0</span>)
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</li>
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<li>
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create transient mediated devices
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(<span class="since">Since 6.5.0</span>)
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</li>
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<li>
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define persistent mediated devices
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(<span class="since">Since 7.3.0</span>)
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</li>
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</ul>
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<p>
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Because mediated devices are instantiated from vendor specific templates,
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simply called 'types', information describing these types is contained
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within the parent device's capabilities (see the example in <a
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href="#PCI">PCI host devices</a>). To list all devices capable of
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creating mediated devices, the following command can be used.
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</p>
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<pre>$ virsh nodedev-list --cap mdev_types</pre>
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<p>
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To see the supported mediated device types on a specific physical device
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use the following:
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</p>
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<pre>$ virsh nodedev-dumpxml <device></pre>
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<p>
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Before creating a mediated device, unbind the device from the respective
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device driver, eg. subchannel I/O driver for a CCW device. Then bind the
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device to the respective VFIO driver. For a CCW device, also unbind the
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corresponding subchannel of the CCW device from the subchannel I/O driver
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and then bind the subchannel (instead of the CCW device) to the vfio_ccw
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driver. The below example shows the unbinding and binding steps for a CCW
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device.
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</p>
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<pre>
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device="0.0.1234"
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subchannel="0.0.0123"
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echo $device > /sys/bus/ccw/devices/$device/driver/unbind
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echo $subchannel > /sys/bus/css/devices/$subchannel/driver/unbind
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echo $subchannel > /sys/bus/css/drivers/vfio_ccw/bind
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</pre>
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<p>
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To instantiate a transient mediated device, create an XML file representing the
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device. See above for information about the mediated device xml format.
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</p>
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<pre>$ virsh nodedev-create <xml-file>
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Node device '<device-name>' created from '<xml-file>'</pre>
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<p>
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If you would like to persistently define the device so that it will be
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maintained across host reboots, use <code>virsh nodedev-define</code>
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instead of <code>nodedev-create</code>:
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</p>
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<pre>$ virsh nodedev-define <xml-file>
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Node device '<device-name>' defined from '<xml-file>'</pre>
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<p>
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To start an instance of this device definition, use the following command:
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</p>
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<pre>$ virsh nodedev-start <device-name></pre>
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<p>
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Active mediated device instances can be stopped using <code>virsh
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nodedev-destroy</code>, and persistent device definitions can be removed
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using <code>virsh nodedev-undefine</code>.
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</p>
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<p>
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If a mediated device is defined persistently, it can also be set to be
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automatically started whenever the host reboots or when the parent device
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becomes available. In order to autostart a mediated device, use the
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following command:
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</p>
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<pre>$ virsh nodedev-autostart <device-name></pre>
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</body>
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</html>
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