mirror of
https://gitlab.com/libvirt/libvirt.git
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5b9819eedc
If a management application wants to use firmware auto selection
feature it can't currently know if the libvirtd it's talking to
support is or not. Moreover, it doesn't know which values that
are accepted for the @firmware attribute of <os/> when parsing
will allow successful start of the domain later, i.e. if the mgmt
application wants to use 'bios' whether there exists a FW
descriptor in the system that describes bios.
This commit then adds 'firmware' enum to <os/> element in
<domainCapabilities/> XML like this:
<enum name='firmware'>
<value>bios</value>
<value>efi</value>
</enum>
We can see both 'bios' and 'efi' listed which means that there
are descriptors for both found in the system (matched with the
machine type and architecture reported in the domain capabilities
earlier and not shown here).
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
535 lines
18 KiB
XML
535 lines
18 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>Domain capabilities XML format</h1>
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<ul id="toc"></ul>
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<h2><a id="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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<p>Some XML elements may be entirely omitted from the domaincapabilities
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XML, depending on what the libvirt driver has filled in. Applications
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should only act on what is explicitly reported in the domaincapabilities
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XML. For example, if <disk supported='yes'/> is present, you can safely
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assume the driver supports <disk> devices. If <disk supported='no'/> is
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present, you can safely assume the driver does NOT support <disk>
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devices. If the <disk> block is omitted entirely, the driver is not
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indicating one way or the other whether it supports <disk> devices, and
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applications should not interpret the missing block to mean any thing in
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particular.</p>
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<h2><a id="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><code>path</code></dt>
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<dd>The full path to the emulator binary.</dd>
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<dt><code>domain</code></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><code>machine</code></dt>
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<dd>The domain's <a href="formatdomain.html#elementsOSBIOS">machine
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type</a>. Since not every hypervisor has a sense of machine types
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this element might be omitted in such drivers.</dd>
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<dt><code>arch</code></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 id="elementsCPUAllocation">CPU Allocation</a></h3>
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<p>Before any devices capability occurs, there might be 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><code>vcpu</code></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 id="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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<enum name='firmware'>
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<value>bios</value>
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<value>efi</value>
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</enum>
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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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<enum name='secure'>
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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>The <code>firmware</code> enum corresponds to
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<code>firmware</code> attribute of the <code>os</code> element.
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Plain presence of this enum means that libvirt is capable of so
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called firmware auto selection. The listed values then represent
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accepted values for the domain attribute. Only values for which
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there exists a firmware descriptor that matches machine type and
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architecture are listed, i.e. those which won't cause a failure
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on domain startup.
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</p>
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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><code>value</code></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><code>type</code></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><code>readonly</code></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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<dt><code>secure</code></dt>
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<dd>Options for the <code>secure</code> attribute of the
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<loader/> element. Note, that <code>yes</code> is listed
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only if there is a firmware that supports it.</dd>
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</dl>
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<h3><a id="elementsCPU">CPU configuration</a></h3>
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<p>
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The <code>cpu</code> element exposes options usable for configuring
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<a href="formatdomain.html#elementsCPU">guest CPUs</a>.
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</p>
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<pre>
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<domainCapabilities>
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...
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<cpu>
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<mode name='host-passthrough' supported='yes'/>
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<mode name='host-model' supported='yes'>
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<model fallback='allow'>Broadwell</model>
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<vendor>Intel</vendor>
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<feature policy='disable' name='aes'/>
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<feature policy='require' name='vmx'/>
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</mode>
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<mode name='custom' supported='yes'>
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<model usable='no'>Broadwell</model>
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<model usable='yes'>Broadwell-noTSX</model>
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<model usable='no'>Haswell</model>
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...
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</mode>
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</cpu>
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...
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<domainCapabilities>
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</pre>
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<p>
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Each CPU mode understood by libvirt is described with a
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<code>mode</code> element which tells whether the particular mode
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is supported and provides (when applicable) more details about it:
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</p>
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<dl>
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<dt><code>host-passthrough</code></dt>
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<dd>No mode specific details are provided.</dd>
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<dt><code>host-model</code></dt>
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<dd>
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If <code>host-model</code> is supported by the hypervisor, the
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<code>mode</code> describes the guest CPU which will be used when
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starting a domain with <code>host-model</code> CPU. The hypervisor
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specifics (such as unsupported CPU models or features, machine type,
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etc.) may be accounted for in this guest CPU specification and thus
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the CPU can be different from the one shown in host capabilities XML.
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This is indicated by the <code>fallback</code> attribute of the
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<code>model</code> sub element: <code>allow</code> means not all
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specifics were accounted for and thus the CPU a guest will see may
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be different; <code>forbid</code> indicates that the CPU a guest will
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see should match this CPU definition.
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</dd>
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<dt><code>custom</code></dt>
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<dd>
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The <code>mode</code> element contains a list of supported CPU
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models, each described by a dedicated <code>model</code> element.
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The <code>usable</code> attribute specifies whether the model can
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be used on the host. A special value <code>unknown</code> indicates
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libvirt does not have enough information to provide the usability
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data.
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</dd>
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</dl>
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<h3><a id="elementsIothreads">I/O Threads</a></h3>
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<p>
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The <code>iothread</code> elements indicates whether or not
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<a href="formatdomain.html#elementsIOThreadsAllocation">I/O threads</a>
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are supported.
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</p>
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<pre>
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<domainCapabilities>
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...
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<iothread supported='yes'/>
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...
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<domainCapabilities>
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</pre>
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<h3><a id="elementsDevices">Devices</a></h3>
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<p>
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Another 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 id="elementsDisks">Hard drives, floppy disks, CDROMs</a></h4>
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<p>Disk capabilities are exposed under the <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>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><code>diskDevice</code></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><code>bus</code></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 id="elementsGraphics">Graphical framebuffers</a></h4>
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<p>Graphics device capabilities are exposed under the
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<code>graphics</code> element. For 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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<graphics supported='yes'>
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<enum name='type'>
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<value>sdl</value>
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<value>vnc</value>
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<value>spice</value>
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</enum>
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</graphics>
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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><code>type</code></dt>
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<dd>Options for the <code>type</code> attribute of the <graphics/>
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element.</dd>
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</dl>
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<h4><a id="elementsVideo">Video device</a></h4>
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<p>Video device capabilities are exposed under the
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<code>video</code> element. For 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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<video supported='yes'>
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<enum name='modelType'>
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<value>vga</value>
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<value>cirrus</value>
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<value>vmvga</value>
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<value>qxl</value>
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<value>virtio</value>
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</enum>
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</video>
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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><code>modelType</code></dt>
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<dd>Options for the <code>type</code> attribute of the
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<video><model> element.</dd>
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</dl>
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<h4><a id="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><code>mode</code></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><code>startupPolicy</code></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><code>subsysType</code></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><code>capsType</code></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><code>pciBackend</code></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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<h3><a id="elementsFeatures">Features</a></h3>
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<p>One more set of XML elements describe the supported features and
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their capabilities. All features occur as children of the main
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<code>features</code> element.</p>
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<pre>
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<domainCapabilities>
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...
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<features>
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<gic supported='yes'>
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<enum name='version'>
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<value>2</value>
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<value>3</value>
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</enum>
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</gic>
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<vmcoreinfo supported='yes'/>
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<genid supported='yes'/>
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<sev>
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<cbitpos>47</cbitpos>
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<reduced-phys-bits>1</reduced-phys-bits>
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</sev>
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</features>
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</domainCapabilities>
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</pre>
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<p>Reported capabilities are expressed as an enumerated list of
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possible values for each of the elements or attributes. For example, the
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<code>gic</code> element has an attribute <code>version</code> which can
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support the values <code>2</code> or <code>3</code>.</p>
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<p>For information about the purpose of each feature, see the
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<a href="formatdomain.html#elementsFeatures">relevant section</a> in
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the domain XML documentation.
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</p>
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<h4><a id="elementsGIC">GIC capabilities</a></h4>
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|
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<p>GIC capabilities are exposed under the <code>gic</code> element.</p>
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<dl>
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<dt><code>version</code></dt>
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<dd>Options for the <code>version</code> attribute of the
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<code>gic</code> element.</dd>
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</dl>
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<h4><a id="elementsvmcoreinfo">vmcoreinfo</a></h4>
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<p>Reports whether the vmcoreinfo feature can be enabled.</p>
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<h4><a id="elementsgenid">genid</a></h4>
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<p>Reports whether the genid feature can be used by the domain.</p>
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<h4><a id="elementsSEV">SEV capabilities</a></h4>
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<p>AMD Secure Encrypted Virtualization (SEV) capabilities are exposed under
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the <code>sev</code> element.
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SEV is an extension to the AMD-V architecture which supports running
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virtual machines (VMs) under the control of a hypervisor. When supported,
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guest owner can create a VM whose memory contents will be transparently
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encrypted with a key unique to that VM.</p>
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<p>
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For more details on SEV feature see:
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<a href="https://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf">
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SEV API spec</a> and <a href="http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf">
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SEV White Paper</a>
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</p>
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<dl>
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<dt><code>cbitpos</code></dt>
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<dd>When memory encryption is enabled, one of the physical address bits
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(aka the C-bit) is utilized to mark if a memory page is protected. The
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C-bit position is Hypervisor dependent.</dd>
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<dt><code>reducedPhysBits</code></dt>
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<dd>When memory encryption is enabled, we lose certain bits in physical
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address space. The number of bits we lose is hypervisor dependent.</dd>
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</dl>
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</body>
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</html>
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