2017-03-27 07:03:02 +00:00
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<?xml version="1.0" encoding="UTF-8"?>
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2017-07-26 17:01:25 +00:00
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<!DOCTYPE html>
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2017-03-27 07:03:02 +00:00
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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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2017-03-27 07:03:02 +00:00
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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>,
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<code>virsh nodedev-dumpxml</code>), which are generic and can be used
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with all devices. It also provides means to create and destroy devices
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(<code>virsh nodedev-create</code>, <code>virsh nodedev-destroy</code>)
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which are meant to be used to create virtual devices, currently only
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supported by NPIV
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(<a href="http://wiki.libvirt.org/page/NPIV_in_libvirt">more info about NPIV)</a>).
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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 two backends to manage the devices, HAL and udev, with the former
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being deprecated in favour of the latter.
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</p>
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<p>
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The generic format of a host device XML can be seen below.
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To identify a device both within the host and the device tree hierarchy,
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the following elements are used:
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</p>
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<dl>
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<dt><code>name</code></dt>
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<dd>
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The device's name will be generated by libvirt using the subsystem,
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like pci and the device's sysfs basename.
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</dd>
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<dt><code>path</code></dt>
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<dd>
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Fully qualified sysfs path to the device.
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</dd>
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<dt><code>parent</code></dt>
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<dd>
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This element identifies the parent node in the device hierarchy. The
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value of the element will correspond with the device parent's
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<code>name</code> element or <code>computer</code> if the device does
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not have any parent.
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</dd>
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<dt><code>driver</code></dt>
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<dd>
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This elements reports the driver in use for this device. The presence
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of this element in the output XML depends on whether the underlying
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device manager (most likely udev) exposes information about the
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driver.
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</dd>
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<dt><code>capability</code></dt>
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<dd>
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Describes the device in terms of feature support. The element has one
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mandatory attribute <code>type</code> the value of which determines
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the type of the device. Currently recognized values for the attribute
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are:
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<code>system</code>,
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<code>pci</code>,
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<code>usb</code>,
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<code>usb_device</code>,
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<code>net</code>,
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<code>scsi</code>,
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<code>scsi_host</code> (<span class="since">Since 0.4.7</span>),
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<code>fc_host</code>,
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<code>vports</code>,
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<code>scsi_target</code> (<span class="since">Since 0.7.3</span>),
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<code>storage</code> (<span class="since">Since 1.0.4</span>),
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<code>scsi_generic</code> (<span class="since">Since 1.0.7</span>),
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<code>drm</code> (<span class="since">Since 3.1.0</span>), and
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<code>mdev</code> (<span class="since">Since 3.4.0</span>).
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This element can be nested in which case it further specifies a
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device's capability. Refer to specific device types to see more values
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for the <code>type</code> attribute which are exclusive.
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</dd>
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</dl>
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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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2017-07-26 14:52:42 +00:00
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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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2017-07-26 14:52:42 +00:00
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<h3><a id="SRIOVCap">SR-IOV capability</a></h3>
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2017-03-27 07:03:02 +00:00
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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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2017-07-26 14:52:42 +00:00
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<h3><a id="MDEVCap">MDEV capability</a></h3>
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<p>
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A PCI 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:
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</p>
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<dl>
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<dt><code>type</code></dt>
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<dd>
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This element describes a mediated device type which acts as an
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abstract template defining a resource allocation for instances of this
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device type. The element has one attribute <code>id</code> which holds
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an official vendor-supplied identifier for the type.
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<span class="since">Since 3.4.0</span>
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</dd>
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<dt><code>name</code></dt>
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<dd>
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The <code>name</code> element holds a vendor-supplied code name for
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the given mediated device type. This is an optional element.
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<span class="since">Since 3.4.0</span>
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</dd>
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<dt><code>deviceAPI</code></dt>
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<dd>
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The value of this element describes how an instance of the given type
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will be presented to the guest by the VFIO framework.
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<span class="since">Since 3.4.0</span>
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</dd>
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<dt><code>availableInstances</code></dt>
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<dd>
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This element reports the current state of resource allocation. In other
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words, how many instances of the given type can still be successfully
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created on the physical device.
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<span class="since">Since 3.4.0</span>
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</dd>
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</dl>
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<p>
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For a more info about mediated devices, refer to the
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<a href="#MDEV">paragraph below</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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2017-07-26 14:52:42 +00:00
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<h2><a id="MDEV">Mediated devices (MDEVs)</a></h2>
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2017-03-29 10:36:31 +00:00
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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.
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</p>
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<p>
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The following sub-elements and attributes are exposed within the
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<code>capability</code> element:
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</p>
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<dl>
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<dt><code>type</code></dt>
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<dd>
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This element describes a mediated device type which acts as an
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abstract template defining a resource allocation for instances of this
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device type. The element has one attribute <code>id</code> which holds
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an official vendor-supplied identifier for the type.
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<span class="since">Since 3.4.0</span>
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</dd>
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<dt><code>iommuGroup</code></dt>
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<dd>
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This element supports a single attribute <code>number</code> which holds
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the IOMMU group number the mediated device belongs to.
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<span class="since">Since 3.4.0</span>
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</dd>
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</dl>
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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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<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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</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
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(see the example in <a href="#PCI">PCI host devices</a>).
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</p>
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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>
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$ ls /sys/class/mdev_bus/<device>/mdev_supported_types</pre>
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<p>
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To manually instantiate a mediated device, use one of the following as a
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reference:
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</p>
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<pre>
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$ uuidgen > /sys/class/mdev_bus/<device>/mdev_supported_types/<type>/create
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...
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$ echo <UUID> > /sys/class/mdev_bus/<device>/mdev_supported_types/<type>/create</pre>
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<p>
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Manual removal of a mediated device is then performed as follows:
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</p>
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<pre>
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$ echo 1 > /sys/bus/mdev/devices/<uuid>/remove</pre>
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2017-03-27 07:03:02 +00:00
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</body>
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</html>
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