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This new module holds and formats capabilities for emulator. If you are about to create a new domain, you may want to know what is the host or hypervisor capable of. To make sure we don't regress on the XML, the formatting is not something left for each driver to implement, rather there's general format function. The domain capabilities is a lockable object (even though the locking is not necessary yet) which uses reference counter. Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
233 lines
7.6 KiB
XML
233 lines
7.6 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Domain capabilities XML format</h1>
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<ul id="toc"></ul>
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<h2><a name="Overview">Overview</a></h2>
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<p>Sometimes, when a new domain is to be created it may come handy to know
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the capabilities of the hypervisor so the correct combination of devices and
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drivers is used. For example, when management application is considering the
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mode for a host device's passthrough there are several options depending not
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only on host, but on hypervisor in question too. If the hypervisor is qemu
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then it needs to be more recent to support VFIO, while legacy KVM is
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achievable just fine with older qemus.</p>
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<p>The main difference between <code
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class="docref">virConnectGetCapabilities</code> and the emulator
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capabilities API is, the former one aims more on the host capabilities
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(e.g. NUMA topology, security models in effect, etc.) while the latter one
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specializes on the hypervisor capabilities.</p>
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<p>While the <a href="formatcaps.html">Driver Capabilities</a> provides the
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host capabilities (e.g NUMA topology, security models in effect, etc.), the
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Domain Capabilities provides the hypervisor specific capabilities for
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Management Applications to query and make decisions regarding what to
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utilize.</p>
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<p>The Domain Capabilities can provide information such as the correct
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combination of devices and drivers that are supported. Knowing which host
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and hypervisor specific options are available or supported would allow the
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management application to choose an appropriate mode for a pass-through
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host device as well as which adapter to utilize.</p>
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<h2><a name="elements">Element and attribute overview</a></h2>
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<p> A new query interface was added to the virConnect API's to retrieve the
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XML listing of the set of domain capabilities (<span class="since">Since
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1.2.7</span>):</p>
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<pre>
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<code class="docref">virConnectGetDomainCapabilities</code>
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</pre>
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<p>The root element that emulator capability XML document starts with has
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name <code>domainCapabilities</code>. It contains at least four direct
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child elements:</p>
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<pre>
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<domainCapabilities>
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<path>/usr/bin/qemu-system-x86_64</path>
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<domain>kvm</domain>
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<machine>pc-i440fx-2.1</machine>
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<arch>x86_64</arch>
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...
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</domainCapabilities>
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</pre>
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<dl>
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<dt>path</dt>
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<dd>The full path to the emulator binary.</dd>
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<dt>domain</dt>
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<dd>Describes the <a href="formatdomain.html#elements">virtualization
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type</a> (or so called domain type).</dd>
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<dt>machine</dt>
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<dd>The domain's <a href="formatdomain.html#elementsOSBIOS">machine
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type</a>.</dd>
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<dt>arch</dt>
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<dd>The domain's <a href="formatdomain.html#elementsOSBIOS">
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architecture</a>.</dd>
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</dl>
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<h3><a name="elementsCPUAllocation">CPU Allocation</a></h3>
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<p>Before any devices capability occurs, there might be a info on domain
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wide capabilities, e.g. virtual CPUs:</p>
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<pre>
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<domainCapabilities>
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...
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<vcpu max='255'/>
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...
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</domainCapabilities>
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</pre>
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<dl>
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<dt>vcpu</dt>
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<dd>The maximum number of supported virtual CPUs</dd>
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</dl>
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<h3><a name="elementsDevices">Devices</a></h3>
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<p>
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The final set of XML elements describe the supported devices and their
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capabilities. All devices occur as children of the main
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<code>devices</code> element.
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</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<disk supported='yes'>
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<enum name='diskDevice'>
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<value>disk</value>
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<value>cdrom</value>
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<value>floppy</value>
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<value>lun</value>
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</enum>
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...
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</disk>
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<hostdev supported='no'/>
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</devices>
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</domainCapabilities>
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</pre>
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<p>Reported capabilities are expressed as an enumerated list of available
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options for each of the element or attribute. For example, the
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<disk/> element has an attribute <code>device</code> which can
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support the values <code>disk</code>, <code>cdrom</code>,
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<code>floppy</code>, or <code>lun</code>.</p>
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<h4><a name="elementsDisks">Hard drives, floppy disks, CDROMs</a></h4>
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<p>Disk capabilities are exposed under <code>disk</code> element. For
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instance:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<disk supported='yes'>
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<enum name='diskDevice'>
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<value>disk</value>
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<value>cdrom</value>
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<value>floppy</value>
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<value>lun</value>
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</enum>
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<enum name='bus'>
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<value>ide</value>
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<value>fdc</value>
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<value>scsi</value>
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<value>virtio</value>
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<value>xen</value>
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<value>usb</value>
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<value>uml</value>
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<value>sata</value>
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<value>sd</value>
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</enum>
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</disk>
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...
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt>diskDevice</dt>
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<dd>Options for the <code>device</code> attribute of the <disk/>
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element.</dd>
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<dt>bus</dt>
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<dd>Options for the <code>bus</code> attribute of the <target/>
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element for a <disk/>.</dd>
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</dl>
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<h4><a name="elementsHostDev">Host device assignment</a></h4>
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<p>Some host devices can be passed through to a guest (e.g. USB, PCI and
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SCSI). Well, only if the following is enabled:</p>
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<pre>
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<domainCapabilities>
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...
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<devices>
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<hostdev supported='yes'>
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<enum name='mode'>
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<value>subsystem</value>
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<value>capabilities</value>
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</enum>
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<enum name='startupPolicy'>
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<value>default</value>
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<value>mandatory</value>
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<value>requisite</value>
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<value>optional</value>
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</enum>
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<enum name='subsysType'>
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<value>usb</value>
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<value>pci</value>
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<value>scsi</value>
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</enum>
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<enum name='capsType'>
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<value>storage</value>
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<value>misc</value>
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<value>net</value>
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</enum>
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<enum name='pciBackend'>
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<value>default</value>
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<value>kvm</value>
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<value>vfio</value>
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<value>xen</value>
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</enum>
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</hostdev>
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</devices>
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</domainCapabilities>
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</pre>
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<dl>
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<dt>mode</dt>
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<dd>Options for the <code>mode</code> attribute of the <hostdev/>
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element.</dd>
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<dt>startupPolicy</dt>
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<dd>Options for the <code>startupPolicy</code> attribute of the
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<hostdev/> element.</dd>
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<dt>subsysType</dt>
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<dd>Options for the <code>type</code> attribute of the <hostdev/>
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element in case of <code>mode="subsystem"</code>.</dd>
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<dt>capsType</dt>
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<dd>Options for the <code>type</code> attribute of the <hostdev/>
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element in case of <code>mode="capabilities"</code>.</dd>
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<dt>pciBackend</dt>
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<dd>Options for the <code>name</code> attribute of the <driver/>
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element.</dd>
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</dl>
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</body>
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</html>
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