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Well, since the link to the virConnectGetDomainCapabilities API is in <pre/> section we must take special care about the spaces around the link. Signed-off-by: Michal Privoznik <mprivozn@redhat.com> Acked-by: Laszlo Ersek <lersek@redhat.com>
282 lines
9.2 KiB
XML
282 lines
9.2 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
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<a href="/html/libvirt-libvirt-host.html#virConnectGetCapabilities">
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<code>virConnectGetCapabilities</code>
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</a>
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and the emulator capabilities API is, the former one aims more on
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the host capabilities (e.g. NUMA topology, security models in
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effect, etc.) while the latter one specializes on the hypervisor
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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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<a href="/html/libvirt-libvirt-domain.html#virConnectGetDomainCapabilities">virConnectGetDomainCapabilities</a>
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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="elementsOSBIOS">BIOS bootloader</a></h3>
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<p>Sometimes users might want to tweak some BIOS knobs or use
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UEFI. For cases like that, <a
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href="formatdomain.html#elementsOSBIOS"><code>os</code></a>
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element exposes what values can be passed to its children.</p>
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<pre>
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<domainCapabilities>
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...
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<os supported='yes'>
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<loader supported='yes'>
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<value>/usr/share/OVMF/OVMF_CODE.fd</value>
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<enum name='type'>
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<value>rom</value>
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<value>pflash</value>
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</enum>
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<enum name='readonly'>
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<value>yes</value>
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<value>no</value>
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</enum>
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</loader>
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</os>
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...
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<domainCapabilities>
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</pre>
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<p>For the <code>loader</code> element, the following can occur:</p>
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<dl>
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<dt>value</dt>
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<dd>List of known loader paths. Currently this is only used
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to advertise known locations of OVMF binaries for qemu. Binaries
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will only be listed if they actually exist on disk.</dd>
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<dt>type</dt>
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<dd>Whether loader is a typical BIOS (<code>rom</code>) or
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an UEFI binary (<code>pflash</code>). This refers to
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<code>type</code> attribute of the <loader/>
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element.</dd>
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<dt>readonly</dt>
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<dd>Options for the <code>readonly</code> attribute of the
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<loader/> element.</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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