<html>
  <body>
    <h1>Domain XML format</h1>

    <ul id="toc"></ul>

    <p>
      This section describes the XML format used to represent domains, there are
      variations on the format based on the kind of domains run and the options
      used to launch them. For hypervisor specific details consult the
      <a href="drivers.html">driver docs</a>
    </p>


    <h2><a name="elements">Element and attribute overview</a></h2>

    <p>
      The root element required for all virtual machines is
      named <code>domain</code>. It has two attributes, the
      <code>type</code> specifies the hypervisor used for running
      the domain. The allowed values are driver specific, but
      include "xen", "kvm", "qemu", "lxc" and "kqemu". The
      second attribute is <code>id</code> which is a unique
      integer identifier for the running guest machine. Inactive
      machines have no id value.
    </p>


    <h3><a name="elementsMetadata">General metadata</a></h3>

<pre>
&lt;domain type='xen' id='3'&gt;
  &lt;name&gt;fv0&lt;/name&gt;
  &lt;uuid&gt;4dea22b31d52d8f32516782e98ab3fa0&lt;/uuid&gt;
  &lt;description&gt;Some human readable description&lt;/description&gt;
  ...</pre>

    <dl>
      <dt><code>name</code></dt>
      <dd>The content of the <code>name</code> element provides
        a short name for the virtual machine. This name should
        consist only of alpha-numeric characters and is required
        to be unique within the scope of a single host. It is
        often used to form the filename for storing the persistent
        configuration file. <span class="since">Since 0.0.1</span></dd>
      <dt><code>uuid</code></dt>
      <dd>The content of the <code>uuid</code> element provides
        a globally unique identifier for the virtual machine.
        The format must be RFC 4122 compliant,
        eg <code>3e3fce45-4f53-4fa7-bb32-11f34168b82b</code>.
        If omitted when defining/creating a new machine, a random
        UUID is generated. It is also possible to provide the UUID
        via a <a href="#elementsSysinfo"><code>sysinfo</code></a>
        specification. <span class="since">Since 0.0.1, sysinfo
        since 0.8.7</span></dd>

      <dt><code>description</code></dt>
      <dd>The content of the <code>description</code> element provides a
      human readable description of the virtual machine. This data is not
      used by libvirt in any way, it can contain any information the user
      wants. <span class="since">Since 0.7.2</span></dd>
    </dl>

    <h3><a name="elementsOS">Operating system booting</a></h3>

    <p>
      There are a number of different ways to boot virtual machines
      each with their own pros and cons.
    </p>

    <h4><a name="elementsOSBIOS">BIOS bootloader</a></h4>

    <p>
      Booting via the BIOS is available for hypervisors supporting
      full virtualization. In this case the BIOS has a boot order
      priority (floppy, harddisk, cdrom, network) determining where
      to obtain/find the boot image.
    </p>

<pre>
  ...
  &lt;os&gt;
    &lt;type&gt;hvm&lt;/type&gt;
    &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
    &lt;boot dev='hd'/&gt;
    &lt;boot dev='cdrom'/&gt;
    &lt;bootmenu enable='yes'/&gt;
    &lt;smbios mode='sysinfo'/&gt;
    &lt;bios useserial='yes'/&gt;
  &lt;/os&gt;
  ...</pre>

    <dl>
      <dt><code>type</code></dt>
      <dd>The content of the <code>type</code> element specifies the
        type of operating system to be booted in the virtual machine.
        <code>hvm</code> indicates that the OS is one designed to run
        on bare metal, so requires full virtualization. <code>linux</code>
        (badly named!) refers to an OS that supports the Xen 3 hypervisor
        guest ABI. There are also two optional attributes, <code>arch</code>
        specifying the CPU architecture to virtualization,
        and <code>machine</code> referring to the machine
        type. The <a href="formatcaps.html">Capabilities XML</a>
        provides details on allowed values for
        these. <span class="since">Since 0.0.1</span></dd>
      <dt><code>loader</code></dt>
      <dd>The optional <code>loader</code> tag refers to a firmware blob
        used to assist the domain creation process. At this time, it is
        only needed by Xen fully virtualized
        domains. <span class="since">Since 0.1.0</span></dd>
      <dt><code>boot</code></dt>
      <dd>The <code>dev</code> attribute takes one of the values "fd", "hd",
        "cdrom" or "network" and is used to specify the next boot device
        to consider. The <code>boot</code> element can be repeated multiple
        times to setup a priority list of boot devices to try in turn. The
        <code>boot</code> element cannot be used if per-device boot elements
        are used (see <a href="#elementsDisks">disks</a>,
        <a href="#elementsNICS">network interfaces</a>, and
        <a href="#elementsUSB">USB and PCI devices</a> sections below).
        <span class="since">Since 0.1.3, per-device boot since 0.8.8</span>
      </dd>
      <dt><code>bootmenu</code></dt>
      <dd> Whether or not to enable an interactive boot menu prompt on guest
      startup. The <code>enable</code> attribute can be either "yes" or "no".
      If not specified, the hypervisor default is used. <span class="since">
      Since 0.8.3</span>
      </dd>
      <dt><code>smbios</code></dt>
      <dd>How to populate SMBIOS information visible in the guest.
      The <code>mode</code> attribute must be specified, and is either
      "emulate" (let the hypervisor generate all values), "host" (copy
      all of Block 0 and Block 1, except for the UUID, from the host's
      SMBIOS values;
      the <a href="html/libvirt-libvirt.html#virConnectGetSysinfo">
      <code>virConnectGetSysinfo</code></a> call can be
      used to see what values are copied), or "sysinfo" (use the values in
      the <a href="#elementsSysinfo">sysinfo</a> element).  If not
      specified, the hypervisor default is used. <span class="since">
      Since 0.8.7</span>
      </dd>
      <dt><code>bios</code></dt>
      <dd>This element has attribute <code>useserial</code> with possible
        values <code>yes</code> or <code>no</code>. It enables or disables
        Serial Graphics Adapter which allows users to see BIOS messages
        on a serial port. Therefore, one needs to have
        <a href="#elementCharSerial">serial port</a> defined.
        <span class="since">Since 0.9.4</span>
      </dd>
    </dl>

    <h4><a name="elementsOSBootloader">Host bootloader</a></h4>

    <p>
      Hypervisors employing paravirtualization do not usually emulate
      a BIOS, and instead the host is responsible to kicking off the
      operating system boot. This may use a pseudo-bootloader in the
      host to provide an interface to choose a kernel for the guest.
      An example is <code>pygrub</code> with Xen.
    </p>

<pre>
  ...
  &lt;bootloader&gt;/usr/bin/pygrub&lt;/bootloader&gt;
  &lt;bootloader_args&gt;--append single&lt;/bootloader_args&gt;
  ...</pre>

    <dl>
      <dt><code>bootloader</code></dt>
      <dd>The content of the <code>bootloader</code> element provides
        a fully qualified path to the bootloader executable in the
        host OS. This bootloader will be run to choose which kernel
        to boot. The required output of the bootloader is dependent
        on the hypervisor in use. <span class="since">Since 0.1.0</span></dd>
      <dt><code>bootloader_args</code></dt>
      <dd>The optional <code>bootloader_args</code> element allows
        command line arguments to be passed to the bootloader.
        <span class="since">Since 0.2.3</span>
        </dd>

    </dl>

    <h4><a name="elementsOSKernel">Direct kernel boot</a></h4>

    <p>
      When installing a new guest OS it is often useful to boot directly
      from a kernel and initrd stored in the host OS, allowing command
      line arguments to be passed directly to the installer. This capability
      is usually available for both para and full virtualized guests.
    </p>

<pre>
  ...
  &lt;os&gt;
    &lt;type&gt;hvm&lt;/type&gt;
    &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
    &lt;kernel&gt;/root/f8-i386-vmlinuz&lt;/kernel&gt;
    &lt;initrd&gt;/root/f8-i386-initrd&lt;/initrd&gt;
    &lt;cmdline&gt;console=ttyS0 ks=http://example.com/f8-i386/os/&lt;/cmdline&gt;
  &lt;/os&gt;
  ...</pre>

    <dl>
      <dt><code>type</code></dt>
      <dd>This element has the same semantics as described earlier in the
        <a href="#elementsOSBIOS">BIOS boot section</a></dd>
      <dt><code>loader</code></dt>
      <dd>This element has the same semantics as described earlier in the
        <a href="#elementsOSBIOS">BIOS boot section</a></dd>
      <dt><code>kernel</code></dt>
      <dd>The contents of this element specify the fully-qualified path
        to the kernel image in the host OS.</dd>
      <dt><code>initrd</code></dt>
      <dd>The contents of this element specify the fully-qualified path
        to the (optional) ramdisk image in the host OS.</dd>
      <dt><code>cmdline</code></dt>
      <dd>The contents of this element specify arguments to be passed to
        the kernel (or installer) at boottime. This is often used to
        specify an alternate primary console (eg serial port), or the
        installation media source / kickstart file</dd>
    </dl>

    <h3><a name="elementsSysinfo">SMBIOS System Information</a></h3>

    <p>
      Some hypervisors allow control over what system information is
      presented to the guest (for example, SMBIOS fields can be
      populated by a hypervisor and inspected via
      the <code>dmidecode</code> command in the guest).  The
      optional <code>sysinfo</code> element covers all such categories
      of information. <span class="since">Since 0.8.7</span>
    </p>

<pre>
  ...
  &lt;os&gt;
    &lt;smbios mode='sysinfo'/&gt;
    ...
  &lt;/os&gt;
  &lt;sysinfo type='smbios'&gt;
    &lt;bios&gt;
      &lt;entry name='vendor'&gt;LENOVO&lt;/entry&gt;
    &lt;/bios&gt;
    &lt;system&gt;
      &lt;entry name='manufacturer'&gt;Fedora&lt;/entry&gt;
      &lt;entry name='vendor'&gt;Virt-Manager&lt;/entry&gt;
    &lt;/system&gt;
  &lt;/sysinfo&gt;
  ...</pre>

    <p>
      The <code>sysinfo</code> element has a mandatory
      attribute <code>type</code> that determine the layout of
      sub-elements, with supported values of:
    </p>

    <dl>
      <dt><code>smbios</code></dt>
      <dd>Sub-elements call out specific SMBIOS values, which will
      affect the guest if used in conjunction with
      the <code>smbios</code> sub-element of
      the <a href="#elementsOS"><code>os</code></a> element.  Each
      sub-element of <code>sysinfo</code> names a SMBIOS block, and
      within those elements can be a list of <code>entry</code>
      elements that describe a field within the block.  The following
      blocks and entries are recognized:
        <dl>
          <dt><code>bios</code></dt>
          <dd>
            This is block 0 of SMBIOS, with entry names drawn from
            "vendor", "version", "date", and "release".
          </dd>
          <dt><code>system</code></dt>
          <dd>
            This is block 1 of SMBIOS, with entry names drawn from
            "manufacturer", "product", "version", "serial", "uuid",
            "sku", and "family".  If a "uuid" entry is provided
            alongside a
            top-level <a href="#elementsMetadata"><code>uuid</code>
            element</a>, the two values must match.
          </dd>
        </dl>
      </dd>
    </dl>

    <h3><a name="elementsCPUAllocation">CPU Allocation</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;vcpu cpuset="1-4,^3,6" current="1"&gt;2&lt;/vcpu&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>vcpu</code></dt>
      <dd>The content of this element defines the maximum number of virtual
        CPUs allocated for the guest OS, which must be between 1 and
        the maximum supported by the hypervisor.  <span class="since">Since
        0.4.4</span>, this element can contain an optional
        <code>cpuset</code> attribute, which is a comma-separated
        list of physical CPU numbers that virtual CPUs can be pinned
        to.  Each element in that list is either a single CPU number,
        a range of CPU numbers, or a caret followed by a CPU number to
        be excluded from a previous range.  <span class="since">Since
        0.8.5</span>, the optional attribute <code>current</code> can
        be used to specify whether fewer than the maximum number of
        virtual CPUs should be enabled.
      </dd>
    </dl>


    <h3><a name="elementsCPUTuning">CPU Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;cputune&gt;
    &lt;vcpupin vcpu="0" cpuset="1-4,^2"/&gt;
    &lt;vcpupin vcpu="1" cpuset="0,1"/&gt;
    &lt;vcpupin vcpu="2" cpuset="2,3"/&gt;
    &lt;vcpupin vcpu="3" cpuset="0,4"/&gt;
    &lt;shares&gt;2048&lt;/shares&gt;
    &lt;period&gt;1000000&lt;/period&gt;
    &lt;quota&gt;-1&lt;/quota&gt;
  &lt;/cputune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>cputune</code></dt>
      <dd>
         The optional <code>cputune</code> element provides details
         regarding the cpu tunable parameters for the domain.
         <span class="since">Since 0.9.0</span>
      </dd>
      <dt><code>vcpupin</code></dt>
      <dd>
        The optional <code>vcpupin</code> element specifies which of host
        physical CPUS the domain VCPU will be pinned to. If this is ommited,
        each VCPU pinned to all the physical CPUS by default. It contains two
        required attributes, the attribute <code>vcpu</code> specifies vcpu id,
        and the attribute <code>cpuset</code> is same as
        attribute <code>cpuset</code>
        of element <code>vcpu</code>. (NB: Only qemu driver support)
        <span class="since">Since 0.9.0</span>
       </dd>
      <dt><code>shares</code></dt>
      <dd>
        The optional <code>shares</code> element specifies the proportional
        weighted share for the domain. If this is ommited, it defaults to
        the OS provided defaults. NB, There is no unit for the value,
        it's a relative measure based on the setting of other VM,
        e.g. A VM configured with value
        2048 will get twice as much CPU time as a VM configured with value 1024.
        <span class="since">Since 0.9.0</span>
      </dd>
      <dt><code>period</code></dt>
      <dd>
        The optional <code>period</code> element specifies the enforcement
        interval(unit: microseconds). Within <code>period</code>, each vcpu of
        the domain will not be allowed to consume more than <code>quota</code>
        worth of runtime. The value should be in range [1000, 1000000]. A period
        with value 0 means no value. (NB: Only qemu driver support)
        <span class="since">Since 0.9.4</span>
      </dd>
      <dt><code>quota</code></dt>
      <dd>
        The optional <code>quota</code> element specifies the maximum allowed
        bandwidth(unit: microseconds). A domain with <code>quota</code> as any
        negative value indicates that the domain has infinite bandwidth, which
        means that it is not bandwidth controlled. The value should be in range
        [1000, 18446744073709551] or less than 0. A quota with value 0 means no
        value. You can use this feature to ensure that all vcpus run at the same
        speed. (NB: Only qemu driver support)
        <span class="since">Since 0.9.4</span>
      </dd>
    </dl>


    <h3><a name="elementsMemoryAllocation">Memory Allocation</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;memory&gt;524288&lt;/memory&gt;
  &lt;currentMemory&gt;524288&lt;/currentMemory&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>memory</code></dt>
      <dd>The maximum allocation of memory for the guest at boot time.
        The units for this value are kilobytes (i.e. blocks of 1024 bytes)</dd>
      <dt><code>currentMemory</code></dt>
      <dd>The actual allocation of memory for the guest. This value can
        be less than the maximum allocation, to allow for ballooning
        up the guests memory on the fly. If this is omitted, it defaults
        to the same value as the <code>memory</code> element</dd>
    </dl>


    <h3><a name="elementsMemoryBacking">Memory Backing</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;memoryBacking&gt;
    &lt;hugepages/&gt;
  &lt;/memoryBacking&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>memoryBacking</code></dt>
      <dd>The optional <code>memoryBacking</code> element, may have an
        <code>hugepages</code> element set within it. This tells the
        hypervisor that the guest should have its memory allocated using
        hugepages instead of the normal native page size.</dd>
    </dl>


    <h3><a name="elementsMemoryTuning">Memory Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;memtune&gt;
    &lt;hard_limit&gt;1048576&lt;/hard_limit&gt;
    &lt;soft_limit&gt;131072&lt;/soft_limit&gt;
    &lt;swap_hard_limit&gt;2097152&lt;/swap_hard_limit&gt;
    &lt;min_guarantee&gt;65536&lt;/min_guarantee&gt;
  &lt;/memtune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>memtune</code></dt>
      <dd> The optional <code>memtune</code> element provides details
        regarding the memory tunable parameters for the domain. If this is
        omitted, it defaults to the OS provided defaults. For QEMU/KVM, the
        parameters are applied to the QEMU process as a whole. Thus, when
        counting them, one needs to add up guest RAM, guest video RAM, and
        some memory overhead of QEMU itself. The last piece is hard to
        determine so one needs guess and try.</dd>
      <dt><code>hard_limit</code></dt>
      <dd> The optional <code>hard_limit</code> element is the maximum memory
        the guest can use. The units for this value are kilobytes (i.e. blocks
        of 1024 bytes)</dd>
      <dt><code>soft_limit</code></dt>
      <dd> The optional <code>soft_limit</code> element is the memory limit to
        enforce during memory contention. The units for this value are
        kilobytes (i.e. blocks of 1024 bytes)</dd>
      <dt><code>swap_hard_limit</code></dt>
      <dd> The optional <code>swap_hard_limit</code> element is the maximum
        memory plus swap the guest can use. The units for this value are
        kilobytes (i.e. blocks of 1024 bytes). This has to be more than
        hard_limit value provided</dd>
      <dt><code>min_guarantee</code></dt>
      <dd> The optional <code>min_guarantee</code> element is the guaranteed
        minimum memory allocation for the guest. The units for this value are
        kilobytes (i.e. blocks of 1024 bytes)</dd>
    </dl>


    <h3><a name="elementsNUMATuning">NUMA Node Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;numatune&gt;
    &lt;memory mode="strict" nodeset="1-4,^3"/&gt;
  &lt;/numatune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>numatune</code></dt>
      <dd>
        The optional <code>numatune</code> element provides details of
        how to tune the performance of a NUMA host via controlling NUMA policy
        for domain process. NB, only supported by QEMU driver.
        <span class='since'>Since 0.9.3</span>
      <dt><code>memory</code></dt>
      <dd>
        The optional <code>memory</code> element specify how to allocate memory
        for the domain process on a NUMA host. It contains two attributes,
        attribute <code>mode</code> is either 'interleave', 'strict',
        or 'preferred',
        attribute <code>nodeset</code> specifies the NUMA nodes, it leads same
        syntax with attribute <code>cpuset</code> of element <code>vcpu</code>.
        <span class='since'>Since 0.9.3</span>
      </dd>
    </dl>


    <h3><a name="elementsBlockTuning">Block I/O Tuning</a></h3>
<pre>
&lt;domain&gt;
  ...
  &lt;blkiotune&gt;
    &lt;weight&gt;800&lt;/weight&gt;
  &lt;/blkiotune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>blkiotune</code></dt>
      <dd> The optional <code>blkiotune</code> element provides the ability
        to tune Blkio cgroup tunable parameters for the domain. If this is
        omitted, it defaults to the OS provided defaults.</dd>
      <dt><code>weight</code></dt>
      <dd> The optional <code>weight</code> element is the I/O weight of the
        guest. The value should be in range [100, 1000].</dd>
    </dl>


    <h3><a name="elementsCPU">CPU model and topology</a></h3>

    <p>
      Requirements for CPU model, its features and topology can be specified
      using the following collection of elements.
      <span class="since">Since 0.7.5</span>
    </p>

<pre>
  ...
  &lt;cpu match='exact'&gt;
    &lt;model&gt;core2duo&lt;/model&gt;
    &lt;vendor&gt;Intel&lt;/vendor&gt;
    &lt;topology sockets='1' cores='2' threads='1'/&gt;
    &lt;feature policy='disable' name='lahf_lm'/&gt;
  &lt;/cpu&gt;
  ...</pre>

    <p>
      In case no restrictions need to be put on CPU model and its features, a
      simpler <code>cpu</code> element can be used.
      <span class="since">Since 0.7.6</span>
    </p>

<pre>
  ...
  &lt;cpu&gt;
    &lt;topology sockets='1' cores='2' threads='1'/&gt;
  &lt;/cpu&gt;
  ...</pre>

    <dl>
      <dt><code>cpu</code></dt>
      <dd>The <code>cpu</code> element is the main container for describing
        guest CPU requirements. Its <code>match</code> attribute specified how
        strictly has the virtual CPU provided to the guest match these
        requirements. <span class="since">Since 0.7.6</span> the
        <code>match</code> attribute can be omitted if <code>topology</code>
        is the only element within <code>cpu</code>. Possible values for the
        <code>match</code> attribute are:

        <dl>
          <dt><code>minimum</code></dt>
          <dd>The specified CPU model and features describes the minimum
            requested CPU.</dd>
          <dt><code>exact</code></dt>
          <dd>The virtual CPU provided to the guest will exactly match the
            specification</dd>
          <dt><code>strict</code></dt>
          <dd>The guest will not be created unless the host CPU does exactly
            match the specification.</dd>
        </dl>

        <span class="since">Since 0.8.5</span> the <code>match</code>
        attribute can be omitted and will default to <code>exact</code>.
      </dd>

      <dt><code>model</code></dt>
      <dd>The content of the <code>model</code> element specifies CPU model
        requested by the guest. The list of available CPU models and their
        definition can be found in <code>cpu_map.xml</code> file installed
        in libvirt's data directory.</dd>

      <dt><code>vendor</code></dt>
      <dd><span class="since">Since 0.8.3</span> the content of the
        <code>vendor</code> element specifies CPU vendor requested by the
        guest. If this element is missing, the guest can be run on a CPU
        matching given features regardless on its vendor. The list of
        supported vendors can be found in <code>cpu_map.xml</code>.</dd>

      <dt><code>topology</code></dt>
      <dd>The <code>topology</code> element specifies requested topology of
        virtual CPU provided to the guest. Three non-zero values have to be
        given for <code>sockets</code>, <code>cores</code>, and
        <code>threads</code>: total number of CPU sockets, number of cores per
        socket, and number of threads per core, respectively.</dd>

      <dt><code>feature</code></dt>
      <dd>The <code>cpu</code> element can contain zero or more
        <code>elements</code> used to fine-tune features provided by the
        selected CPU model. The list of known feature names can be found in
        the same file as CPU models. The meaning of each <code>feature</code>
        element depends on its <code>policy</code> attribute, which has to be
        set to one of the following values:

        <dl>
          <dt><code>force</code></dt>
          <dd>The virtual CPU will claim the feature is supported regardless
            of it being supported by host CPU.</dd>
          <dt><code>require</code></dt>
          <dd>Guest creation will fail unless the feature is supported by host
            CPU.</dd>
          <dt><code>optional</code></dt>
          <dd>The feature will be supported by virtual CPU if and only if it
            is supported by host CPU.</dd>
          <dt><code>disable</code></dt>
          <dd>The feature will not be supported by virtual CPU.</dd>
          <dt><code>forbid</code></dt>
          <dd>Guest creation will fail if the feature is supported by host
            CPU.</dd>
        </dl>

        <span class="since">Since 0.8.5</span> the <code>policy</code>
        attribute can be omitted and will default to <code>require</code>.
      </dd>
    </dl>

    <h3><a name="elementsLifecycle">Lifecycle control</a></h3>

    <p>
      It is sometimes necessary to override the default actions taken
      when a guest OS triggers a lifecycle operation. The following
      collections of elements allow the actions to be specified. A
      common use case is to force a reboot to be treated as a poweroff
      when doing the initial OS installation. This allows the VM to be
      re-configured for the first post-install bootup.
    </p>

<pre>
  ...
  &lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
  &lt;on_reboot&gt;restart&lt;/on_reboot&gt;
  &lt;on_crash&gt;restart&lt;/on_crash&gt;
  ...</pre>

    <dl>
      <dt><code>on_poweroff</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest requests a poweroff.</dd>
      <dt><code>on_reboot</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest requests a reboot.</dd>
      <dt><code>on_crash</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest crashes.</dd>
    </dl>

    <p>
      Each of these states allow for the same four possible actions.
    </p>

    <dl>
      <dt><code>destroy</code></dt>
      <dd>The domain will be terminated completely and all resources
        released</dd>
      <dt><code>restart</code></dt>
      <dd>The domain will be terminated, and then restarted with
        the same configuration</dd>
      <dt><code>preserve</code></dt>
      <dd>The domain will be terminated, and its resource preserved
        to allow analysis.</dd>
      <dt><code>rename-restart</code></dt>
      <dd>The domain will be terminated, and then restarted with
        a new name</dd>
    </dl>

    <p>
      on_crash supports these additional
      actions <span class="since">since 0.8.4</span>.
    </p>

    <dl>
      <dt><code>coredump-destroy</code></dt>
      <dd>The crashed domain's core will be dumped, and then the
        domain will be terminated completely and all resources
        released</dd>
      <dt><code>coredump-restart</code></dt>
      <dd>The crashed domain's core will be dumped, and then the
        domain will be restarted with the same configuration</dd>
    </dl>

    <h3><a name="elementsFeatures">Hypervisor features</a></h3>

    <p>
      Hypervisors may allow certain CPU / machine features to be
      toggled on/off.
    </p>

<pre>
  ...
  &lt;features&gt;
    &lt;pae/&gt;
    &lt;acpi/&gt;
    &lt;apic/&gt;
    &lt;hap/&gt;
  &lt;/features&gt;
  ...</pre>

    <p>
      All features are listed within the <code>features</code>
      element, omitting a togglable feature tag turns it off.
      The available features can be found by asking
      for the <a href="formatcaps.html">capabilities XML</a>,
      but a common set for fully virtualized domains are:
    </p>

    <dl>
      <dt><code>pae</code></dt>
      <dd>Physical address extension mode allows 32-bit guests
        to address more than 4 GB of memory.</dd>
      <dt><code>acpi</code></dt>
      <dd>ACPI is useful for power management, for example, with
        KVM guests it is required for graceful shutdown to work.
      </dd>
      <dt><code>hap</code></dt>
      <dd>Enable use of Hardware Assisted Paging if available in
        the hardware.
      </dd>
    </dl>

    <h3><a name="elementsTime">Time keeping</a></h3>

    <p>
      The guest clock is typically initialized from the host clock.
      Most operating systems expect the hardware clock to be kept
      in UTC, and this is the default. Windows, however, expects
      it to be in so called 'localtime'.
    </p>

<pre>
  ...
  &lt;clock offset="localtime"&gt;
    &lt;timer name="rtc" tickpolicy="catchup" track="guest"&gt;
      &lt;catchup threshold=123 slew=120 limit=10000/&gt;
    &lt;/timer&gt;
    &lt;timer name="pit" tickpolicy="none"/&gt;
  &lt;/clock&gt;
  ...</pre>

    <dl>
      <dt><code>clock</code></dt>
      <dd>
        <p>The <code>offset</code> attribute takes four possible
          values, allowing fine grained control over how the guest
          clock is synchronized to the host. NB, not all hypervisors
          support all modes.</p>
        <dl>
          <dt><code>utc</code></dt>
          <dd>
            The guest clock will always be synchronized to UTC when
            booted</dd>
          <dt><code>localtime</code></dt>
          <dd>
            The guest clock will be synchronized to the host's configured
            timezone when booted, if any.
          </dd>
          <dt><code>timezone</code></dt>
          <dd>
            The guest clock will be synchronized to the requested timezone
            using the <code>timezone</code> attribute.
            <span class="since">Since 0.7.7</span>
          </dd>
          <dt><code>variable</code></dt>
          <dd>
            The guest clock will have an arbitrary offset applied
            relative to UTC. The delta relative to UTC is specified
            in seconds, using the <code>adjustment</code> attribute.
            The guest is free to adjust the RTC over time an expect
            that it will be honoured at next reboot. This is in
            contrast to 'utc' mode, where the RTC adjustments are
            lost at each reboot. <span class="since">Since 0.7.7</span>
          </dd>
        </dl>
        <p>
          A <code>clock</code> may have zero or more
          <code>timer</code>sub-elements. <span class="since">Since
          0.8.0</span>
        </p>
      </dd>
      <dt><code>timer</code></dt>
      <dd>
        <p>
          Each timer element requires a <code>name</code> attribute,
          and has other optional attributes that depend on
          the <code>name</code> specified.  Various hypervisors
          support different combinations of attributes.
        </p>
        <dl>
          <dt><code>name</code></dt>
          <dd>
            The <code>name</code> attribute selects which timer is
            being modified, and can be one of "platform", "pit",
            "rtc", "hpet", or "tsc".
          </dd>
          <dt><code>track</code></dt>
          <dd>
            The <code>track</code> attribute specifies what the timer
            tracks, and can be "boot", "guest", or "wall".
            Only valid for <code>name="rtc"</code>
            or <code>name="platform"</code>.
          </dd>
          <dt><code>tickpolicy</code></dt>
          <dd>
            The <code>tickpolicy</code> attribute determines how
            missed ticks in the guest are handled, and can be "delay",
            "catchup", "merge", or "discard".  If the policy is
            "catchup", there can be further details in
            the <code>catchup</code> sub-element.
            <dl>
              <dt><code>catchup</code></dt>
              <dd>
                The <code>catchup</code> element has three optional
                attributes, each a positive integer.  The attributes
                are <code>threshold</code>, <code>slew</code>,
                and <code>limit</code>.
              </dd>
            </dl>
          </dd>
          <dt><code>frequency</code></dt>
          <dd>
            The <code>frequency</code> attribute is an unsigned
            integer specifying the frequency at
            which <code>name="tsc"</code> runs.
          </dd>
          <dt><code>mode</code></dt>
          <dd>
            The <code>mode</code> attribute controls how
            the <code>name="tsc"</code> timer is managed, and can be
            "auto", "native", "emulate", "paravirt", or "smpsafe".
            Other timers are always emulated.
          </dd>
          <dt><code>present</code></dt>
          <dd>
            The <code>present</code> attribute can be "yes" or "no" to
            specify whether a particular timer is available to the guest.
          </dd>
        </dl>
      </dd>
    </dl>

    <h3><a name="elementsDevices">Devices</a></h3>

    <p>
      The final set of XML elements are all used to describe devices
      provided to the guest domain. All devices occur as children
      of the main <code>devices</code> element.
      <span class="since">Since 0.1.3</span>
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;emulator&gt;/usr/lib/xen/bin/qemu-dm&lt;/emulator&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>emulator</code></dt>
      <dd>
        The contents of the <code>emulator</code> element specify
        the fully qualified path to the device model emulator binary.
        The <a href="formatcaps.html">capabilities XML</a> specifies
        the recommended default emulator to use for each particular
        domain type / architecture combination.
      </dd>
    </dl>

    <h4><a name="elementsDisks">Hard drives, floppy disks, CDROMs</a></h4>

    <p>
      Any device that looks like a disk, be it a floppy, harddisk,
      cdrom, or paravirtualized driver is specified via the <code>disk</code>
      element.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;disk type='file' snapshot='external'&gt;
      &lt;driver name="tap" type="aio" cache="default"/&gt;
      &lt;source file='/var/lib/xen/images/fv0'/&gt;
      &lt;target dev='hda' bus='ide'/&gt;
      &lt;boot order='2'/&gt;
      &lt;encryption type='...'&gt;
        ...
      &lt;/encryption&gt;
      &lt;shareable/&gt;
      &lt;serial&gt;
        ...
      &lt;/serial&gt;
    &lt;/disk&gt;
      ...
    &lt;disk type='network'&gt;
      &lt;driver name="qemu" type="raw" io="threads" ioeventfd="on" event_idx="off"/&gt;
      &lt;source protocol="sheepdog" name="image_name"&gt;
        &lt;host name="hostname" port="7000"/&gt;
      &lt;/source&gt;
      &lt;target dev="hdb" bus="ide"/&gt;
      &lt;boot order='1'/&gt;
      &lt;transient/&gt;
      &lt;address type='drive' controller='0' bus='1' unit='0'/&gt;
    &lt;/disk&gt;
    &lt;disk type='block' device='cdrom'&gt;
      &lt;driver name='qemu' type='raw'/&gt;
      &lt;target def='hdc' bus='ide'/&gt;
      &lt;readonly/&gt;
    &lt;/disk&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>disk</code></dt>
      <dd>The <code>disk</code> element is the main container for describing
        disks. The <code>type</code> attribute is either "file",
        "block", "dir", or "network"
        and refers to the underlying source for the disk. The optional
        <code>device</code> attribute indicates how the disk is to be exposed
        to the guest OS. Possible values for this attribute are "floppy", "disk"
        and "cdrom", defaulting to "disk".  The
        optional <code>snapshot</code> attribute indicates the default
        behavior of the disk during disk snapshots: "internal"
        requires a file format such as qcow2 that can store both the
        snapshot and the data changes since the snapshot;
        "external" will separate the snapshot from the live data; and
        "no" means the disk will not participate in snapshots.
        Read-only disks default to "no", while the default for other
        disks depends on the hypervisor's capabilities.  Some
        hypervisors allow a per-snapshot choice as well,
        during <a href="formatsnapshot.html">domain snapshot
        creation</a>.  Not all snapshot modes are supported;
        for example, <code>snapshot='yes'</code> with a transient disk
        generally does not make sense.  <span class="since">Since 0.0.3;
        "device" attribute since 0.1.4;
        "network" attribute since 0.8.7; "snapshot" since
        0.9.5</span></dd>
      <dt><code>source</code></dt>
      <dd>If the disk <code>type</code> is "file", then
        the <code>file</code> attribute specifies the fully-qualified
        path to the file holding the disk. If the disk
        <code>type</code> is "block", then the <code>dev</code>
        attribute specifies the path to the host device to serve as
        the disk. If the disk <code>type</code> is "network", then
        the <code>protocol</code> attribute specifies the protocol to
        access to the requested image; possible values are "nbd",
        "rbd", and "sheepdog".  If the <code>protocol</code> attribute
        is "rbd" or "sheepdog", an additional
        attribute <code>name</code> is mandatory to specify which
        image to be used.  When the disk <code>type</code> is
        "network", the <code>source</code> may have zero or
        more <code>host</code> sub-elements used to specify the hosts
        to connect.
        <span class="since">Since 0.0.3</span></dd>
      <dt><code>target</code></dt>
      <dd>The <code>target</code> element controls the bus / device
        under which the disk is exposed to the guest
        OS. The <code>dev</code> attribute indicates the "logical"
        device name. The actual device name specified is not
        guaranteed to map to the device name in the guest OS. Treat it
        as a device ordering hint.  The optional <code>bus</code>
        attribute specifies the type of disk device to emulate;
        possible values are driver specific, with typical values being
        "ide", "scsi", "virtio", "xen" or "usb". If omitted, the bus type is
        inferred from the style of the device name. eg, a device named 'sda'
        will typically be exported using a SCSI bus.
        <span class="since">Since 0.0.3; <code>bus</code> attribute since 0.4.3;
        "usb" attribute value since after 0.4.4</span></dd>
      <dt><code>driver</code></dt>
      <dd>
        The optional driver element allows specifying further details
        related to the hypervisor driver used to provide the disk.
        <span class="since">Since 0.1.8</span>
        <ul>
          <li>
            If the hypervisor supports multiple backend drivers, then
            the <code>name</code> attribute selects the primary
            backend driver name, while the optional <code>type</code>
            attribute provides the sub-type.  For example, xen
            supports a name of "tap", "tap2", "phy", or "file", with a
            type of "aio", while qemu only supports a name of "qemu",
            but multiple types including "raw", "bochs", "qcow2", and
            "qed".
          </li>
          <li>
            The optional <code>cache</code> attribute controls the
            cache mechanism, possible values are "default", "none",
            "writethrough", "writeback", and "directsync". "directsync"
            is like "writethrough", but it bypasses the host page
            cache.
            <span class="since">Since 0.6.0</span>
          </li>
          <li>
            The optional <code>error_policy</code> attribute controls
            how the hypervisor will behave on an error, possible
            values are "stop", "ignore", and "enospace".
            <span class="since">Since 0.8.0</span>
          </li>
          <li>
            The optional <code>io</code> attribute controls specific
            policies on I/O; qemu guests support "threads" and
            "native". <span class="since">Since 0.8.8</span>
          </li>
          <li>
            The optional <code>ioeventfd</code> attribute allows users to
            set <a href='https://patchwork.kernel.org/patch/43390/'>
            domain I/O asynchronous handling</a> for disk device.
            The default is left to the discretion of the hypervisor.
            Accepted values are "on" and "off". Enabling this allows
            qemu to execute VM while a separate thread handles I/O.
            Typically guests experiencing high system CPU utilization
            during I/O will benefit from this. On the other hand,
            on overloaded host it could increase guest I/O latency.
            <span class="since">Since 0.9.3 (QEMU and KVM only)</span>
            <b>In general you should leave this option alone, unless you
            are very certain you know what you are doing.</b>
          </li>
          <li>
            The optional <code>event_idx</code> attribute controls
            some aspects of device event processing. The value can be
            either 'on' or 'off' - if it is on, it will reduce the
            number of interupts and exits for the guest. The default
            is determined by QEMU; usually if the feature is
            supported, default is on. In case there is a situation
            where this behavior is suboptimal, this attribute provides
            a way to force the feature off.
            <span class="since">Since 0.9.5 (QEMU and KVM only)</span>
            <b>In general you should leave this option alone, unless you
            are very certain you know what you are doing.</b>
          </li>
        </ul>
      </dd>
      <dt><code>boot</code></dt>
      <dd>Specifies that the disk is bootable. The <code>order</code>
        attribute determines the order in which devices will be tried during
        boot sequence. The per-device <code>boot</code> elements cannot be
        used together with general boot elements in
        <a href="#elementsOSBIOS">BIOS bootloader</a> section.
        <span class="since">Since 0.8.8</span>
      </dd>
      <dt><code>encryption</code></dt>
      <dd>If present, specifies how the volume is encrypted.  See
        the <a href="formatstorageencryption.html">Storage Encryption</a> page
        for more information.
      </dd>
      <dt><code>readonly</code></dt>
      <dd>If present, this indicates the device cannot be modified by
        the guest.  For now, this is the default for disks with
        attribute <code>type='cdrom'</code>.
      </dd>
      <dt><code>shareable</code></dt>
      <dd>If present, this indicates the device is expected to be shared
          between domains (assuming the hypervisor and OS support this),
          which means that caching should be deactivated for that device.
      </dd>
      <dt><code>transient</code></dt>
      <dd>If present, this indicates that changes to the device
        contents should be reverted automatically when the guest
        exits.  With some hypervisors, marking a disk transient
        prevents the domain from participating in migration or
        snapshots. <span class="since">Since 0.9.5</span>
      </dd>
      <dt><code>serial</code></dt>
      <dd>If present, this specify serial number of virtual hard drive.
          For example, it may look
          like <code>&lt;serial&gt;WD-WMAP9A966149&lt;/serial&gt;</code>.
          <span class="since">Since 0.7.1</span>
      </dd>
      <dt><code>host</code></dt>
      <dd>The <code>host</code> element has two attributes "name" and "port",
        which specify the hostname and the port number. The meaning of this
        element and the number of the elements depend on the protocol attribute.
        <table class="top_table">
          <tr>
            <th> Protocol </th>
            <th> Meaning </th>
            <th> Number of hosts </th>
          </tr>
          <tr>
            <td> nbd </td>
            <td> a server running nbd-server </td>
            <td> only one </td>
          </tr>
          <tr>
            <td> rbd </td>
            <td> monitor servers of RBD </td>
            <td> one or more </td>
          </tr>
          <tr>
            <td> sheepdog </td>
            <td> one of the sheepdog servers (default is localhost:7000) </td>
            <td> zero or one </td>
          </tr>
        </table>
      </dd>
      <dt><code>address</code></dt>
      <dd>If present, the <code>address</code> element ties the disk
        to a given slot of a controller (the
        actual <code>&lt;controller&gt;</code> device can often be
        inferred by libvirt, although it can
        be <a href="#elementsControllers">explicitly specified</a>).
        The <code>type</code> attribute is mandatory, and is typically
        "pci" or "drive".  For a "pci" controller, additional
        attributes for <code>bus</code>, <code>slot</code>,
        and <code>function</code> must be present, as well as an
        optional <code>domain</code>.  For a "drive" controller,
        additional attributes <code>controller</code>, <code>bus</code>,
        and <code>unit</code> are available, each defaulting to 0.
      </dd>
    </dl>

    <h4><a name="elementsFilesystems">Filesystems</a></h4>

    <p>
      A directory on the host that can be accessed directly from the guest.
      <span class="since">since 0.3.3, since 0.8.5 for QEMU/KVM</span>
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;filesystem type='template'&gt;
      &lt;source name='my-vm-template'/&gt;
      &lt;target dir='/'/&gt;
    &lt;/filesystem&gt;
    &lt;filesystem type='mount' accessmode='passthrough'&gt;
      &lt;source dir='/export/to/guest'/&gt;
      &lt;target dir='/import/from/host'/&gt;
      &lt;readonly/&gt;
    &lt;/filesystem&gt;
    ...
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>filesystem</code></dt>
      <dd>

      The filesystem attribute <code>type</code> specifies the type of the
      <code>source</code>. The possible values are:

        <dl>
        <dt><code>type='mount'</code></dt>
        <dd>
        A host directory to mount in the guest. Used by LXC,
        OpenVZ <span class="since">(since 0.6.2)</span>
        and QEMU/KVM <span class="since">(since 0.8.5)</span>.
        This is the default <code>type</code> if one is not specified.
        </dd>
        <dt><code>type='template'</code></dt>
        <dd>
        OpenVZ filesystem template. Only used by OpenVZ driver.
        </dd>
        <dt><code>type='file'</code></dt>
        <dd>
        Currently unused.
        </dd>
        <dt><code>type='block'</code></dt>
        <dd>
        Currently unused.
        </dd>
        </dl>

      The filesystem block has an optional attribute <code>accessmode</code>
      which specifies the security mode for accessing the source
      <span class="since">(since 0.8.5)</span>. Currently this only works
      with <code>type='mount'</code> for the QEMU/KVM driver. The possible
      values are:

        <dl>
        <dt><code>accessmode='passthrough'</code></dt>
        <dd>
        The <code>source</code> is accessed with the permissions of the
        user inside the guest. This is the default <code>accessmode</code> if
        one is not specified.
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-05/msg02673.html">More info</a>
        </dd>
        <dt><code>accessmode='mapped'</code></dt>
        <dd>
        The <code>source</code> is accessed with the permissions of the
        hypervisor (QEMU process).
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-05/msg02673.html">More info</a>
        </dd>
        <dt><code>accessmode='squash'</code></dt>
        <dd>
        Similar to 'passthrough', the exception is that failure of
        privileged operations like 'chown' are ignored. This makes a
        passthrough-like mode usable for people who run the hypervisor
        as non-root.
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-09/msg00121.html">More info</a>
        </dd>
        </dl>

      </dd>

      <dt><code>source</code></dt>
      <dd>
        The resource on the host that is being accessed in the guest. The
        <code>name</code> attribute must be used with
        <code>type='template'</code>, and the <code>dir</code> attribute must
        be used with <code>type='mount'</code>
      </dd>

      <dt><code>target</code></dt>
      <dd>
        Where the <code>source</code> can be accessed in the guest. For
        most drivers this is an automatic mount point, but for QEMU/KVM
        this is merely an arbitrary string tag that is exported to the
        guest as a hint for where to mount.
      </dd>

      <dt><code>readonly</code></dt>
      <dd>
      An optional <code>readonly</code> attribute is available but currently
      unused.
      </dd>
    </dl>

    <h4><a name="elementsControllers">Controllers</a></h4>

    <p>
      Many devices that have an <code>&lt;address&gt;</code>
      sub-element are designed to work with a controller to manage
      related devices.  Normally, libvirt can automatically infer such
      controllers without requiring explicit XML markup, but sometimes
      it is necessary to provide an explicit controller element.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;controller type='ide' index='0'/&gt;
    &lt;controller type='virtio-serial' index='0' ports='16' vectors='4'/&gt;
    &lt;controller type='virtio-serial' index='1'&gt;
      &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/&gt;
    &lt;/controller&gt;
    ...
  &lt;/devices&gt;
  ...</pre>

    <p>
      Each controller has a mandatory attribute <code>type</code>,
      which must be one of "ide", "fdc", "scsi", "sata", "usb",
      "ccid", or "virtio-serial", and a mandatory
      attribute <code>index</code> which is the decimal integer
      describing in which order the bus controller is encountered (for
      use in <code>controller</code> attributes
      of <code>&lt;address&gt;</code> elements).  The "virtio-serial"
      controller has two additional optional
      attributes <code>ports</code> and <code>vectors</code>, which
      control how many devices can be connected through the
      controller.  A "scsi" controller has an optional
      attribute <code>model</code>, which is one of "auto",
      "buslogic", "lsilogic", "lsias1068", or "vmpvscsi".
      A "usb" controller has an optional attribute <code>model</code>,
      which is one of "piix3-uhci", "piix4-uhci", "ehci",
      "ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3",
      "vt82c686b-uhci" or "pci-ohci".
    </p>

    <p>
      For controllers that are themselves devices on a PCI or USB bus,
      an optional sub-element <code>&lt;address&gt;</code> can specify
      the exact relationship of the controller to its master bus, with
      semantics like any other device's <code>address</code>
      sub-element.
    </p>

    <p>
      USB companion controllers have an optional
      sub-element <code>&lt;master&gt;</code> to specify the exact
      relationship of the companion to its master controller.
      A companion controller is on the same bus as its master, so
      the companion <code>index</code> value should be equal.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;controller type='usb' index='0' model='ich9-ehci1'&gt;
      &lt;address type='pci' domain='0' bus='0' slot='4' function='7'/&gt;
    &lt;/controller&gt;
    &lt;controller type='usb' index='0' model='ich9-uhci1'&gt;
      &lt;master startport='0'/&gt;
      &lt;address type='pci' domain='0' bus='0' slot='4' function='0'/&gt;
    &lt;/controller&gt;
    ...
  &lt;/devices&gt;
  ...</pre>

    <h4><a name="elementsLease">Device leases</a></h4>

    <p>
      When using a lock manager, it may be desirable to record device leases
      against a VM. The lock manager will ensure the VM won't start unless
      the leases can be acquired.
    </p>

<pre>
  ...
  &lt;devices&gt;
    ...
    &lt;lease&gt;
      &lt;lockspace&gt;somearea&lt;/lockspace&gt;
      &lt;key&gt;somekey&lt;/key&gt;
      &lt;target path='/some/lease/path' offset='1024'/&gt;
    &lt;/lease&gt;
    ...
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt>lockspace</dt>
      <dd>This is an arbitrary string, identifying the lockspace
        within which the key is held. Lock managers may impose
        extra restrictions on the format, or length of the lockspace
        name.</dd>
      <dt>key</dt>
      <dd>This is an arbitrary string, uniquely identifying the
        lease to be acquired. Lock managers may impose extra
        restrictions on the format, or length of the key.
      </dd>
      <dt>target</dt>
      <dd>This is the fully qualified path of the file associated
        with the lockspace. The offset specifies where the lease
        is stored within the file. If the lock manager does not
        require a offset, just pass 0.
      </dd>
    </dl>

    <h4><a name="elementsUSB">USB and PCI devices</a></h4>

    <p>
      USB and PCI devices attached to the host can be passed through
      to the guest using
      the <code>hostdev</code> element. <span class="since">since after
      0.4.4 for USB and 0.6.0 for PCI (KVM only)</span>:
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;hostdev mode='subsystem' type='usb'&gt;
      &lt;source&gt;
        &lt;vendor id='0x1234'/&gt;
        &lt;product id='0xbeef'/&gt;
      &lt;/source&gt;
      &lt;boot order='2'/&gt;
    &lt;/hostdev&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>or:</p>

<pre>
  ...
  &lt;devices&gt;
    &lt;hostdev mode='subsystem' type='pci' managed='yes'&gt;
      &lt;source&gt;
        &lt;address bus='0x06' slot='0x02' function='0x0'/&gt;
      &lt;/source&gt;
      &lt;boot order='1'/&gt;
    &lt;/hostdev&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>hostdev</code></dt>
      <dd>The <code>hostdev</code> element is the main container for describing
        host devices. For usb device passthrough <code>mode</code> is always
        "subsystem" and <code>type</code> is "usb" for a USB device and "pci"
        for a PCI device. When <code>managed</code> is "yes" for a PCI
        device, it is detached from the host before being passed on to
        the guest.</dd>
      <dt><code>source</code></dt>
      <dd>The source element describes the device as seen from the host.
      The USB device can either be addressed by vendor / product id using the
      <code>vendor</code> and <code>product</code> elements or by the device's
      address on the hosts using the <code>address</code> element.
      PCI devices on the other hand can only be described by their
      <code>address</code></dd>
      <dt><code>vendor</code>, <code>product</code></dt>
      <dd>The <code>vendor</code> and <code>product</code> elements each have an
      <code>id</code> attribute that specifies the USB vendor and product id.
      The ids can be given in decimal, hexadecimal (starting with 0x) or
      octal (starting with 0) form.</dd>
      <dt><code>boot</code></dt>
      <dd>Specifies that the device is bootable. The <code>order</code>
      attribute determines the order in which devices will be tried during
      boot sequence. The per-device <code>boot</code> elements cannot be
      used together with general boot elements in
      <a href="#elementsOSBIOS">BIOS bootloader</a> section.
      <span class="since">Since 0.8.8</span></dd>
      <dt><code>address</code></dt>
      <dd>The <code>address</code> element for USB devices has a
      <code>bus</code> and <code>device</code> attribute to specify the
      USB bus and device number the device appears at on the host.
      The values of these attributes can be given in decimal, hexadecimal
      (starting with 0x) or octal (starting with 0) form.
      For PCI devices the element carries 3 attributes allowing to designate
      the device as can be found with the <code>lspci</code> or
      with <code>virsh nodedev-list</code>. The
      <code>bus</code> attribute allows the hexadecimal values 0 to ff, the
      <code>slot</code> attribute allows the hexadecimal values 0 to 1f, and
      the <code>function</code> attribute allows the hexadecimal values 0 to
      7. There is also an optional <code>domain</code> attribute for the
      PCI domain, with hexadecimal values 0 to ffff, but it is currently
      not used by qemu.</dd>
    </dl>

    <h4><a name="elementsRedir">Redirected devices</a></h4>

    <p>
      USB device redirection through a character device is
      supported <span class="since">since after 0.9.5 (KVM
      only)</span>:
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;redirdev bus='usb' type='tcp'&gt;
      &lt;source mode='connect' host='localhost' service='4000'/&gt;
    &lt;/redirdev&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>redirdev</code></dt>
      <dd>The <code>redirdev</code> element is the main container for
        describing redirected devices. <code>bus</code> must be "usb"
        for a USB device.

        An additional attribute <code>type</code> is required,
        matching one of the
        supported <a href="#elementsConsole">serial device</a> types,
        to describe the host side of the
        tunnel; <code>type='tcp'</code>
        or <code>type='spicevmc'</code> (which uses the usbredir
        channel of a <a href="#elementsGraphics">SPICE graphics
        device</a>) are typical.  Further sub-elements, such
        as <code>&lt;source&gt;</code>, may be required according to
        the given type, although a <code>&lt;target&gt;</code>
        sub-element is not required (since the consumer of the
        character device is the hypervisor itself, rather than a
        device visible in the guest).</dd>

    </dl>

    <h4><a name="elementsSmartcard">Smartcard devices</a></h4>

    <p>
      A virtual smartcard device can be supplied to the guest via the
      <code>smartcard</code> element. A USB smartcard reader device on
      the host cannot be used on a guest with simple device
      passthrough, since it will then not be available on the host,
      possibly locking the host computer when it is "removed".
      Therefore, some hypervisors provide a specialized virtual device
      that can present a smartcard interface to the guest, with
      several modes for describing how credentials are obtained from
      the host or even a from a channel created to a third-party
      smartcard provider. <span class="since">Since 0.8.8</span>
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;smartcard mode='host'/&gt;
    &lt;smartcard mode='host-certificates'&gt;
      &lt;certificate&gt;cert1&lt;/certificate&gt;
      &lt;certificate&gt;cert2&lt;/certificate&gt;
      &lt;certificate&gt;cert3&lt;/certificate&gt;
      &lt;database&gt;/etc/pki/nssdb/&lt;/database&gt;
    &lt;/smartcard&gt;
    &lt;smartcard mode='passthrough' type='tcp'&gt;
      &lt;source mode='bind' host='127.0.0.1' service='2001'/&gt;
      &lt;protocol type='raw'/&gt;
      &lt;address type='ccid' controller='0' slot='0'/&gt;
    &lt;/smartcard&gt;
    &lt;smartcard mode='passthrough' type='spicevmc'/&gt;
  &lt;/devices&gt;
  ...
</pre>

    <p>
      The <code>&lt;smartcard&gt;</code> element has a mandatory
      attribute <code>mode</code>.  The following modes are supported;
      in each mode, the guest sees a device on its USB bus that
      behaves like a physical USB CCID (Chip/Smart Card Interface
      Device) card.
    </p>

    <dl>
      <dt><code>mode='host'</code></dt>
      <dd>The simplest operation, where the hypervisor relays all
      requests from the guest into direct access to the host's
      smartcard via NSS.  No other attributes or sub-elements are
      required.  See below about the use of an
      optional <code>&lt;address&gt;</code> sub-element.</dd>

      <dt><code>mode='host-certificates'</code></dt>
      <dd>Rather than requiring a smartcard to be plugged into the
      host, it is possible to provide three NSS certificate names
      residing in a database on the host.  These certificates can be
      generated via the command <code>certutil -d /etc/pki/nssdb -x -t
      CT,CT,CT -S -s CN=cert1 -n cert1</code>, and the resulting three
      certificate names must be supplied as the content of each of
      three <code>&lt;certificate&gt;</code> sub-elements.  An
      additional sub-element <code>&lt;database&gt;</code> can specify
      the absolute path to an alternate directory (matching
      the <code>-d</code> option of the <code>certutil</code> command
      when creating the certificates); if not present, it defaults to
      /etc/pki/nssdb.</dd>

      <dt><code>mode='passthrough'</code></dt>
      <dd>Rather than having the hypervisor directly communicate with
      the host, it is possible to tunnel all requests through a
      secondary character device to a third-party provider (which may
      in turn be talking to a smartcard or using three certificate
      files).  In this mode of operation, an additional
      attribute <code>type</code> is required, matching one of the
      supported <a href="#elementsConsole">serial device</a> types, to
      describe the host side of the tunnel; <code>type='tcp'</code>
      or <code>type='spicevmc'</code> (which uses the smartcard
      channel of a <a href="#elementsGraphics">SPICE graphics
      device</a>) are typical.  Further sub-elements, such
      as <code>&lt;source&gt;</code>, may be required according to the
      given type, although a <code>&lt;target&gt;</code> sub-element
      is not required (since the consumer of the character device is
      the hypervisor itself, rather than a device visible in the
      guest).</dd>
    </dl>

    <p>
      Each mode supports an optional
      sub-element <code>&lt;address&gt;</code>, which fine-tunes the
      correlation between the smartcard and a ccid bus controller.
      If present, the element must have an attribute
      of <code>type='ccid'</code> as well as a <code>bus</code>
      attribute listing the index of the bus that the smartcard
      utilizes.  An optional <code>slot</code> attribute lists which
      slot within the bus.  For now, qemu only supports at most one
      smartcard, with an address of bus=0 slot=0.
    </p>

    <h4><a name="elementsNICS">Network interfaces</a></h4>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='xenbr0'/&gt;
      &lt;mac address='00:16:3e:5d:c7:9e'/&gt;
      &lt;script path='vif-bridge'/&gt;
      &lt;boot order='1'/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      There are several possibilities for specifying a network
      interface visible to the guest.  Each subsection below provides
      more details about common setup options.  Additionally,
      each <code>&lt;interface&gt;</code> element has an
      optional <code>&lt;address&gt;</code> sub-element that can tie
      the interface to a particular pci slot, with
      attribute <code>type='pci'</code> and additional
      attributes <code>domain</code>, <code>bus</code>, <code>slot</code>,
      and <code>function</code> as appropriate.
    </p>

    <h5><a name="elementsNICSVirtual">Virtual network</a></h5>

    <p>
      <strong><em>
      This is the recommended config for general guest connectivity on
      hosts with dynamic / wireless networking configs (or multi-host
      environments where the host hardware details are described
      separately in a <code>&lt;network&gt;</code>
      definition <span class="since">Since 0.9.4</span>).
      </em></strong>
    </p>

    <p>

      Provides a connection whose details are described by the named
      network definition. Depending on the virtual network's "forward
      mode" configuration, the network may be totally isolated
      (no <code>&lt;forward&gt;</code> element given), NAT'ing to an
      explicit network device or to the default route
      (<code>&lt;forward mode='nat'&gt;</code>), routed with no NAT
      (<code>&lt;forward mode='route'/&gt;</code>), or connected
      directly to one of the host's network interfaces (via macvtap)
      or bridge devices ((<code>&lt;forward
      mode='bridge|private|vepa|passthrough'/&gt;</code> <span class="since">Since
      0.9.4</span>)
    </p>
    <p>
      For networks with a forward mode of bridge, private, vepa, and
      passthrough, it is assumed that the host has any necessary DNS
      and DHCP services already setup outside the scope of libvirt. In
      the case of isolated, nat, and routed networks, DHCP and DNS are
      provided on the virtual network by libvirt, and the IP range can
      be determined by examining the virtual network config with
      '<code>virsh net-dumpxml [networkname]</code>'. There is one
      virtual network called 'default' setup out of the box which does
      NAT'ing to the default route and has an IP range
      of <code>192.168.122.0/255.255.255.0</code>. Each guest will
      have an associated tun device created with a name of vnetN,
      which can also be overridden with the &lt;target&gt; element
      (see
      <a href="#elementsNICSTargetOverride">overriding the target element</a>).
    </p>
    <p>
      When the source of an interface is a network,
      a <code>portgroup</code> can be specified along with the name of
      the network; one network may have multiple portgroups defined,
      with each portgroup containing slightly different configuration
      information for different classes of network
      connections. <span class="since">Since 0.9.4</span>). Also,
      similar to <code>direct</code> network connections (described
      below), a connection of type <code>network</code> may specify
      a <code>virtportprofile</code> element, with configuration data
      to be forwarded to a vepa or 802.1Qbh compliant switch.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
    &lt;/interface&gt;
    ...
    &lt;interface type='network'&gt;
      &lt;source network='default' portgroup='engineering'/&gt;
      &lt;target dev='vnet7'/&gt;
      &lt;mac address="00:11:22:33:44:55"/&gt;
      &lt;virtualport type='802.1Qbg'&gt;
        &lt;parameters managerid='11' typeid='1193047' typeidversion='2' instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/&gt;
      &lt;/virtualport&gt;

    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <h5><a name="elementsNICSBridge">Bridge to LAN</a></h5>

    <p>
      <strong><em>
      This is the recommended config for general guest connectivity on
      hosts with static wired networking configs
      </em></strong>
    </p>

    <p>
      Provides a bridge from the VM directly onto the LAN. This assumes
      there is a bridge device on the host which has one or more of the hosts
      physical NICs enslaved. The guest VM will have an associated tun device
      created with a name of vnetN, which can also be overridden with the
      &lt;target&gt; element (see
      <a href="#elementsNICSTargetOverride">overriding the target element</a>).
      The tun device will be enslaved to the bridge. The IP range / network
      configuration is whatever is used on the LAN. This provides the guest VM
      full incoming &amp; outgoing net access just like a physical machine.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='bridge'&gt;
      &lt;source bridge='br0'/&gt;
    &lt;/interface&gt;
    ...
    &lt;interface type='bridge'&gt;
      &lt;source bridge='br0'/&gt;
      &lt;target dev='vnet7'/&gt;
      &lt;mac address="00:11:22:33:44:55"/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <h5><a name="elementsNICSSlirp">Userspace SLIRP stack</a></h5>

    <p>
      Provides a virtual LAN with NAT to the outside world. The virtual
      network has DHCP &amp; DNS services and will give the guest VM addresses
      starting from <code>10.0.2.15</code>. The default router will be
      <code>10.0.2.2</code> and the DNS server will be <code>10.0.2.3</code>.
      This networking is the only option for unprivileged users who need their
      VMs to have outgoing access.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='user'/&gt;
    ...
    &lt;interface type='user'&gt;
      &lt;mac address="00:11:22:33:44:55"/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>


    <h5><a name="elementsNICSEthernet">Generic ethernet connection</a></h5>

    <p>
      Provides a means for the administrator to execute an arbitrary script
      to connect the guest's network to the LAN. The guest will have a tun
      device created with a name of vnetN, which can also be overridden with the
      &lt;target&gt; element. After creating the tun device a shell script will
      be run which is expected to do whatever host network integration is
      required. By default this script is called /etc/qemu-ifup but can be
      overridden.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='ethernet'/&gt;
    ...
    &lt;interface type='ethernet'&gt;
      &lt;target dev='vnet7'/&gt;
      &lt;script path='/etc/qemu-ifup-mynet'/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <h5><a name="elementsNICSDirect">Direct attachment to physical interface</a></h5>

    <p>
      Provides direct attachment of the virtual machine's NIC to the given
      physial interface of the host.
      <span class="since">Since 0.7.7 (QEMU and KVM only)</span><br/>
      This setup requires the Linux macvtap
      driver to be available. <span class="since">(Since Linux 2.6.34.)</span>
      One of the modes 'vepa'
      ( <a href="http://www.ieee802.org/1/files/public/docs2009/new-evb-congdon-vepa-modular-0709-v01.pdf">
      'Virtual Ethernet Port Aggregator'</a>), 'bridge' or 'private'
      can be chosen for the operation mode of the macvtap device, 'vepa'
      being the default mode. The individual modes cause the delivery of
      packets to behave as follows:
    </p>

    <dl>
      <dt><code>vepa</code></dt>
      <dd>All VMs' packets are sent to the external bridge. Packets
      whose destination is a VM on the same host as where the
      packet originates from are sent back to the host by the VEPA
      capable bridge (today's bridges are typically not VEPA capable).</dd>
      <dt><code>bridge</code></dt>
      <dd>Packets whose destination is on the same host as where they
      originate from are directly delivered to the target macvtap device.
      Both origin and destination devices need to be in bridge mode
      for direct delivery. If either one of them is in <code>vepa</code> mode,
      a VEPA capable bridge is required.</dd>
      <dt><code>private</code></dt>
      <dd>All packets are sent to the external bridge and will only be
      delivered to a target VM on the same host if they are sent through an
      external router or gateway and that device sends them back to the
      host. This procedure is followed if either the source or destination
      device is in <code>private</code> mode.</dd>
      <dt><code>passthrough</code></dt>
      <dd>This feature attaches a virtual function of a SRIOV capable
      NIC directly to a VM without losing the migration capability.
      All packets are sent to the VF/IF of the configured network device.
      Depending on the capabilities of the device additional prerequisites or
      limitations may apply; for example, on Linux this requires
      kernel 2.6.38 or newer. <span class="since">Since 0.9.2</span></dd>
    </dl>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='direct'/&gt;
    ...
    &lt;interface type='direct'&gt;
      &lt;source dev='eth0' mode='vepa'/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      The network access of direct attached virtual machines can be
      managed by the hardware switch to which the physical interface
      of the host machine is connected to.
    </p>
    <p>
      The interface can have additional parameters as shown below,
      if the switch is conforming to the IEEE 802.1Qbg standard.
      The parameters of the virtualport element are documented in more detail
      in the IEEE 802.1Qbg standard. The values are network specific and
      should be provided by the network administrator. In 802.1Qbg terms,
      the Virtual Station Interface (VSI) represents the virtual interface
      of a virtual machine. <span class="since">Since 0.8.2</span>
    </p>
    <p>
      Please note that IEEE 802.1Qbg requires a non-zero value for the
      VLAN ID.
    </p>
    <dl>
      <dt><code>managerid</code></dt>
      <dd>The VSI Manager ID identifies the database containing the VSI type
        and instance definitions. This is an integer value and the
        value 0 is reserved.</dd>
      <dt><code>typeid</code></dt>
      <dd>The VSI Type ID identifies a VSI type characterizing the network
        access. VSI types are typically managed by network administrator.
        This is an integer value.
      </dd>
      <dt><code>typeidversion</code></dt>
      <dd>The VSI Type Version allows multiple versions of a VSI Type.
        This is an integer value.
      </dd>
      <dt><code>instanceid</code></dt>
      <dd>The VSI Instance ID Identifier is generated when a VSI instance
        (i.e. a virtual interface of a virtual machine) is created.
        This is a globally unique identifier.
      </dd>
    </dl>
<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='direct'/&gt;
    ...
    &lt;interface type='direct'&gt;
      &lt;source dev='eth0.2' mode='vepa'/&gt;
      &lt;virtualport type="802.1Qbg"&gt;
        &lt;parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/&gt;
      &lt;/virtualport&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      The interface can have additional parameters as shown below
      if the switch is conforming to the IEEE 802.1Qbh standard.
      The values are network specific and should be provided by the
      network administrator. <span class="since">Since 0.8.2</span>
    </p>
    <dl>
      <dt><code>profileid</code></dt>
      <dd>The profile ID contains the name of the port profile that is to
        be applied onto this interface.  This name is resolved by the port
        profile database into the network parameters from the port profile,
        and those network parameters will be applied to this interface.
      </dd>
    </dl>
  <pre>
  ...
  &lt;devices&gt;
    &lt;interface type='direct'/&gt;
    ...
    &lt;interface type='direct'&gt;
      &lt;source dev='eth0' mode='private'/&gt;
      &lt;virtualport type='802.1Qbh'&gt;
        &lt;parameters profileid='finance'/&gt;
      &lt;/virtualport&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...
  </pre>

    <h5><a name="elementsNICSMulticast">Multicast tunnel</a></h5>

    <p>
      A multicast group is setup to represent a virtual network. Any VMs
      whose network devices are in the same multicast group can talk to each
      other even across hosts. This mode is also available to unprivileged
      users. There is no default DNS or DHCP support and no outgoing network
      access. To provide outgoing network access, one of the VMs should have a
      2nd NIC which is connected to one of the first 4 network types and do the
      appropriate routing. The multicast protocol is compatible with that used
      by user mode linux guests too. The source address used must be from the
      multicast address block.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='mcast'&gt;
      &lt;source address='230.0.0.1' port='5558'/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <h5><a name="elementsNICSTCP">TCP tunnel</a></h5>

    <p>
      A TCP client/server architecture provides a virtual network. One VM
      provides the server end of the network, all other VMS are configured as
      clients. All network traffic is routed between the VMs via the server.
      This mode is also available to unprivileged users. There is no default
      DNS or DHCP support and no outgoing network access. To provide outgoing
      network access, one of the VMs should have a 2nd NIC which is connected
      to one of the first 4 network types and do the appropriate routing.</p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='server'&gt;
      &lt;source address='192.168.0.1' port='5558'/&gt;
    &lt;/interface&gt;
    ...
    &lt;interface type='client'&gt;
    &lt;source address='192.168.0.1' port='5558'/&gt;
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <h5><a name="elementsNICSModel">Setting the NIC model</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet1'/&gt;
      <b>&lt;model type='ne2k_pci'/&gt;</b>
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      For hypervisors which support this, you can set the model of
      emulated network interface card.
    </p>

    <p>
      The values for <code>type</code> aren't defined specifically by
      libvirt, but by what the underlying hypervisor supports (if
      any).  For QEMU and KVM you can get a list of supported models
      with these commands:
    </p>

<pre>
qemu -net nic,model=? /dev/null
qemu-kvm -net nic,model=? /dev/null
</pre>

    <p>
      Typical values for QEMU and KVM include:
      ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio
    </p>

    <h5><a name="elementsDriverBackendOptions">Setting NIC driver-specific options</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet1'/&gt;
      &lt;model type='virtio'/&gt;
      <b>&lt;driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off'/&gt;</b>
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      Some NICs may have tunable driver-specific options. These are
      set as attributes of the <code>driver</code> sub-element of the
      interface definition. Currently the following attributes are
      available for the <code>"virtio"</code> NIC driver:
    </p>

    <dl>
      <dt><code>name</code></dt>
      <dd>
        The optional <code>name</code> attribute forces which type of
        backend driver to use. The value can be either 'qemu' (a
        user-space backend) or 'vhost' (a kernel backend, which
        requires the vhost module to be provided by the kernel); an
        attempt to require the vhost driver without kernel support
        will be rejected.  If this attribute is not present, then the
        domain defaults to 'vhost' if present, but silently falls back
        to 'qemu' without error.
        <span class="since">Since 0.8.8 (QEMU and KVM only)</span>
      </dd>
      <dt><code>txmode</code></dt>
      <dd>
        The <code>txmode</code> attribute specifies how to handle
        transmission of packets when the transmit buffer is full. The
        value can be either 'iothread' or 'timer'.
        <span class="since">Since 0.8.8 (QEMU and KVM only)</span><br/><br/>

        If set to 'iothread', packet tx is all done in an iothread in
        the bottom half of the driver (this option translates into
        adding "tx=bh" to the qemu commandline -device virtio-net-pci
        option).<br/><br/>

        If set to 'timer', tx work is done in qemu, and if there is
        more tx data than can be sent at the present time, a timer is
        set before qemu moves on to do other things; when the timer
        fires, another attempt is made to send more data.<br/><br/>

        The resulting difference, according to the qemu developer who
        added the option is: "bh makes tx more asynchronous and reduces
        latency, but potentially causes more processor bandwidth
        contention since the cpu doing the tx isn't necessarily the
        cpu where the guest generated the packets."<br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>ioeventfd</code></dt>
      <dd>
        This optional attribute allows users to set
        <a href='https://patchwork.kernel.org/patch/43390/'>
        domain I/O asynchronous handling</a> for interface device.
        The default is left to the discretion of the hypervisor.
        Accepted values are "on" and "off". Enabling this allows
        qemu to execute VM while a separate thread handles I/O.
        Typically guests experiencing high system CPU utilization
        during I/O will benefit from this. On the other hand,
        on overloaded host it could increase guest I/O latency.
        <span class="since">Since 0.9.3 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>event_idx</code></dt>
      <dd>
        The <code>event_idx</code> attribute controls some aspects of
        device event processing. The value can be either 'on' or 'off'
        - if it is on, it will reduce the number of interupts and
        exits for the guest. The default is determined by QEMU;
        usually if the feature is supported, default is on. In case
        there is a situation where this behavior is suboptimal, this
        attribute provides a way to force the feature off.
        <span class="since">Since 0.9.5 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
    </dl>

    <h5><a name="elementsNICSTargetOverride">Overriding the target element</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      <b>&lt;target dev='vnet1'/&gt;</b>
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      If no target is specified, certain hypervisors will
      automatically generate a name for the created tun device. This
      name can be manually specifed, however the name <i>must not
      start with either 'vnet' or 'vif'</i>, which are prefixes
      reserved by libvirt and certain hypervisors. Manually specified
      targets using these prefixes will be ignored.
    </p>

    <h5><a name="elementsNICSBoot">Specifying boot order</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet1'/&gt;
      <b>&lt;boot order='1'/&gt;</b>
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      For hypervisors which support this, you can set exact NIC which should
      be used for network boot. The <code>order</code> attribute determines
      the order in which devices will be tried during boot sequence. The
      per-device <code>boot</code> elements cannot be used together with
      general boot elements in
      <a href="#elementsOSBIOS">BIOS bootloader</a> section.
      <span class="since">Since 0.8.8</span>
    </p>

    <h5><a name="elementQoS">Quality of service</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet0'/&gt;
      <b>&lt;bandwidth&gt;
        &lt;inbound average='1000' peak='5000' burst='1024'/&gt;
        &lt;outbound average='128' peak='256' burst='256'/&gt;
      &lt;/bandwidth&gt;</b>
    &lt;/interface&gt;
  &lt;devices&gt;
  ...</pre>

    <p>
      This part of interface XML provides setting quality of service. Incoming
      and outgoing traffic can be shaped independently. The
      <code>bandwidth</code> element can have at most one <code>inbound</code>
      and at most one <code>outbound</code> child elements. Leaving any of these
      children element out result in no QoS applied on that traffic direction.
      So, when you want to shape only domain's incoming traffic, use
      <code>inbound</code> only, and vice versa. Each of these elements have one
      mandatory attribute <code>average</code>. It specifies average bit rate on
      interface being shaped. Then there are two optional attributes:
      <code>peak</code>, which specifies maximum rate at which interface can send
      data, and <code>burst</code>, amount of bytes that can be burst at
      <code>peak</code> speed. Accepted values for attributes are integer
      numbers. The units for <code>average</code> and <code>peak</code> attributes
      are kilobytes per second, and for the <code>burst</code> just kilobytes.
      <span class="since">Since 0.9.4</span>
    </p>

    <h4><a name="elementsInput">Input devices</a></h4>

    <p>
      Input devices allow interaction with the graphical framebuffer
      in the guest virtual machine. When enabling the framebuffer, an
      input device is automatically provided. It may be possible to
      add additional devices explicitly, for example,
      to provide a graphics tablet for absolute cursor movement.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;input type='mouse' bus='usb'/&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>input</code></dt>
      <dd>The <code>input</code> element has one mandatory attribute,
        the <code>type</code> whose value can be either 'mouse' or
        'tablet'. The latter provides absolute
        cursor movement, while the former uses relative movement. The optional
        <code>bus</code> attribute can be used to refine the exact device type.
        It takes values "xen" (paravirtualized), "ps2" and "usb".</dd>
    </dl>

    <p>
      The <code>input</code> element has an optional
      sub-element <code>&lt;address&gt;</code> which can tie the
      device to a particular PCI slot.
    </p>

    <h4><a name="elementsHub">Hub devices</a></h4>

    <p>
      A hub is a device that expands a single port into several so
      that there are more ports available to connect devices to a host
      system.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;hub type='usb'/&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>hub</code></dt>
      <dd>The <code>hub</code> element has one mandatory attribute,
        the <code>type</code> whose value can only be 'usb'.</dd>
    </dl>

    <p>
      The <code>hub</code> element has an optional
      sub-element <code>&lt;address&gt;</code> which can tie the
      device to a particular controller.
    </p>

    <h4><a name="elementsGraphics">Graphical framebuffers</a></h4>

    <p>
      A graphics device allows for graphical interaction with the
      guest OS. A guest will typically have either a framebuffer
      or a text console configured to allow interaction with the
      admin.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;graphics type='sdl' display=':0.0'/&gt;
    &lt;graphics type='vnc' port='5904'&gt;
      &lt;listen type='address' address='1.2.3.4'/&gt;
    &lt;/graphics&gt;
    &lt;graphics type='rdp' autoport='yes' multiUser='yes' /&gt;
    &lt;graphics type='desktop' fullscreen='yes'/&gt;
    &lt;graphics type='spice'&gt;
      &lt;listen type='network' network='rednet'/&gt;
    &lt;/graphics&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>graphics</code></dt>
      <dd>The <code>graphics</code> element has a mandatory <code>type</code>
        attribute which takes the value "sdl", "vnc", "rdp" or "desktop":
        <dl>
          <dt><code>"sdl"</code></dt>
          <dd>
            This displays a window on the host desktop, it can take 3
            optional arguments: a <code>display</code> attribute for
            the display to use, an <code>xauth</code> attribute for
            the authentication identifier, and an
            optional <code>fullscreen</code> attribute accepting
            values 'yes' or 'no'.
          </dd>
          <dt><code>"vnc"</code></dt>
          <dd>
            Starts a VNC server. The <code>port</code> attribute
            specifies the TCP port number (with -1 as legacy syntax
            indicating that it should be
            auto-allocated). The <code>autoport</code> attribute is
            the new preferred syntax for indicating autoallocation of
            the TCP port to use.  The <code>listen</code> attribute is
            an IP address for the server to listen
            on. The <code>passwd</code> attribute provides a VNC
            password in clear text. The <code>keymap</code> attribute
            specifies the keymap to use. It is possible to set a limit
            on the validity of the password be giving an
            timestamp <code>passwdValidTo='2010-04-09T15:51:00'</code>
            assumed to be in UTC. The <code>connected</code> attribute
            allows control of connected client during password changes.
            VNC accepts <code>keep</code> value only.
            <span class="since">since 0.9.3</span>
            NB, this may not be supported by all hypervisors.<br/>  <br/>
            Rather than using listen/port, QEMU supports a
            <code>socket</code> attribute for listening on a unix
            domain socket path.<span class="since">Since 0.8.8</span>
          </dd>
          <dt><code>"spice"</code></dt>
          <dd>
            <p>
              Starts a SPICE server. The <code>port</code> attribute
              specifies the TCP port number (with -1 as legacy syntax
              indicating that it should be auto-allocated),
              while <code>tlsPort</code> gives an alternative secure
              port number. The <code>autoport</code> attribute is the
              new preferred syntax for indicating autoallocation of
              both port numbers.  The <code>listen</code> attribute is
              an IP address for the server to listen
              on. The <code>passwd</code> attribute provides a SPICE
              password in clear text. The <code>keymap</code>
              attribute specifies the keymap to use. It is possible to
              set a limit on the validity of the password be giving an
              timestamp <code>passwdValidTo='2010-04-09T15:51:00'</code>
              assumed to be in UTC. The <code>connected</code> attribute
              allows control of connected client during password changes.
              SPICE accepts <code>keep</code> to keep client connected,
              <code>disconnect</code> to disconnect client and
              <code>fail</code> to fail changing password.
              <span class="since">Since 0.9.3</span>
              NB, this may not be supported by all hypervisors.
              <span class="since">"spice" since 0.8.6</span>.
            </p>
            <p>
              When SPICE has both a normal and TLS secured TCP port
              configured, it can be desirable to restrict what
              channels can be run on each port.  This is achieved by
              adding one or more &lt;channel&gt; elements inside the
              main &lt;graphics&gt; element. Valid channel names
              include <code>main</code>, <code>display</code>,
              <code>inputs</code>, <code>cursor</code>,
              <code>playback</code>, <code>record</code>;
              and <span class="since">since
              0.8.8</span>: <code>smartcard</code>.
            </p>
            <pre>
  &lt;graphics type='spice' port='-1' tlsPort='-1' autoport='yes'&gt;
    &lt;channel name='main' mode='secure'/&gt;
    &lt;channel name='record' mode='insecure'/&gt;
    &lt;image compression='auto_glz'/&gt;
    &lt;streaming mode='filter'/&gt;
    &lt;clipboard copypaste='no'/&gt;
  &lt;/graphics&gt;</pre>
            <p>
              Spice supports variable compression settings for audio,
              images and streaming, <span class="since">since
              0.9.1</span>.  These settings are accessible via
              the <code>compression</code> attribute in all following
              elements: <code>image</code> to set image compression
              (accepts <code>auto_glz</code>, <code>auto_lz</code>,
              <code>quic</code>, <code>glz</code>, <code>lz</code>,
              <code>off</code>), <code>jpeg</code> for JPEG
              compression for images over wan
              (accepts <code>auto</code>, <code>never</code>,
              <code>always</code>), <code>zlib</code> for configuring
              wan image compression (accepts <code>auto</code>,
              <code>never</code>, <code>always</code>)
              and <code>playback</code> for enabling audio stream
              compression (accepts <code>on</code> or <code>off</code>).
            </p>
            <p>
              Streaming mode is set by the <code>streaming</code>
              element, settings it's <code>mode</code> attribute to one
              of <code>filter</code>, <code>all</code>
              or <code>off</code>, <span class="since">since 0.9.2</span>.
            </p>
            <p>
              Copy &amp; Paste functionality (via Spice agent) is set
              by the <code>clipboard</code> element. It is enabled by
              default, and can be disabled by setting
              the <code>copypaste</code> property
              to <code>no</code>, <span class="since">since
              0.9.3</span>.
            </p>
          </dd>
          <dt><code>"rdp"</code></dt>
          <dd>
            Starts a RDP server. The <code>port</code> attribute
            specifies the TCP port number (with -1 as legacy syntax
            indicating that it should be
            auto-allocated). The <code>autoport</code> attribute is
            the new preferred syntax for indicating autoallocation of
            the TCP port to use. The <code>replaceUser</code>
            attribute is a boolean deciding whether multiple
            simultaneous connections to the VM are permitted.
            The <code>multiUser</code> whether the existing connection
            must be dropped and a new connection must be established
            by the VRDP server, when a new client connects in single
            connection mode.
          </dd>
          <dt><code>"desktop"</code></dt>
          <dd>
            This value is reserved for VirtualBox domains for the
            moment. It displays a window on the host desktop,
            similarly to "sdl", but using the VirtualBox viewer. Just
            like "sdl", it accepts the optional
            attributes <code>display</code>
            and <code>fullscreen</code>.
          </dd>
        </dl>
      </dd>
    </dl>

    <p>
      Rather than putting the address information used to set up the
      listening socket for graphics types <code>vnc</code>
      and <code>spice</code> in
      the <code>&lt;graphics&gt;</code> <code>listen</code> attribute,
      a separate subelement of <code>&lt;graphics&gt;</code>,
      called <code>&lt;listen&gt;</code> can be specified (see the
      examples above)<span class="since">since
      0.9.4</span>. <code>&lt;listen&gt;</code> accepts the following
      attributes:
    </p>
    <dl>
      <dt><code>type</code></dt>
      <dd>Set to either <code>address</code>
        or <code>network</code>. This tells whether this listen
        element is specifying the address to be used directly, or by
        naming a network (which will then be used to determine an
        appropriate address for listening).
      </dd>
    </dl>
    <dl>
      <dt><code>address</code></dt>
      <dd>if <code>type='address'</code>, the <code>address</code>
        attribute will contain either an IP address or hostname (which
        will be resolved to an IP address via a DNS query) to listen
        on. In the "live" XML of a running domain, this attribute will
        be set to the IP address used for listening, even
        if <code>type='network'</code>.
      </dd>
    </dl>
    <dl>
      <dt><code>network</code></dt>
      <dd>if <code>type='network'</code>, the <code>network</code>
        attribute will contain the name of a network in libvirt's list
        of configured networks. The named network configuration will
        be examined to determine an appropriate listen address. For
        example, if the network has an IPv4 address in its
        configuration (e.g. if it has a forward type
        of <code>route</code>, <code>nat</code>, or no forward type
        (isolated)), the first IPv4 address listed in the network's
        configuration will be used. If the network is describing a
        host bridge, the first IPv4 address associated with that
        bridge device will be used, and if the network is describing
        one of the 'direct' (macvtap) modes, the first IPv4 address of
        the first forward dev will be used.
      </dd>
    </dl>

    <h4><a name="elementsVideo">Video devices</a></h4>
    <p>
      A video device.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;video&gt;
      &lt;model type='vga' vram='8192' heads='1'&gt;
        &lt;acceleration accel3d='yes' accel3d='yes'/&gt;
      &lt;/model&gt;
    &lt;/video&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>video</code></dt>
      <dd>
        The <code>video</code> element is the a container for describing
        video devices. For backwards compatability, if no <code>video</code>
        is set but there is a <code>graphics</code> in domain xml, then libvirt
        will add a default <code>video</code> according to the guest type.
        For a guest of type "kvm", the default <code>video</code> for it is:
        <code>type</code> with value "cirrus", <code>vram</code> with value
        "9216", and <code>heads</code> with value "1".
      </dd>

      <dt><code>model</code></dt>
      <dd>
        The <code>model</code> element has a mandatory <code>type</code>
        attribute which takes the value "vga", "cirrus", "vmvga", "xen",
        "vbox", or "qxl" (<span class="since">since 0.8.6</span>)
        depending on the hypervisor features available.
        You can also provide the amount of video memory in kilobytes using
        <code>vram</code> and the number of screen with <code>heads</code>.
      </dd>

      <dt><code>acceleration</code></dt>
      <dd>
        If acceleration should be enabled (if supported) using the
        <code>accel3d</code> and <code>accel2d</code> attributes in the
        <code>acceleration</code> element.
      </dd>

      <dt><code>address</code></dt>
      <dd>
        The optional <code>address</code> sub-element can be used to
        tie the video device to a particular PCI slot.
      </dd>
    </dl>

    <h4><a name="elementsConsole">Consoles, serial, parallel &amp; channel devices</a></h4>

    <p>
      A character device provides a way to interact with the virtual machine.
      Paravirtualized consoles, serial ports, parallel ports and channels are
      all classed as character devices and so represented using the same syntax.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;parallel type='pty'&gt;
      &lt;source path='/dev/pts/2'/&gt;
      &lt;target port='0'/&gt;
    &lt;/parallel&gt;
    &lt;serial type='pty'&gt;
      &lt;source path='/dev/pts/3'/&gt;
      &lt;target port='0'/&gt;
    &lt;/serial&gt;
    &lt;console type='pty'&gt;
      &lt;source path='/dev/pts/4'/&gt;
      &lt;target port='0'/&gt;
    &lt;/console&gt;
    &lt;channel type='unix'&gt;
      &lt;source mode='bind' path='/tmp/guestfwd'/&gt;
      &lt;target type='guestfwd' address='10.0.2.1' port='4600'/&gt;
    &lt;/channel&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      In each of these directives, the top-level element name (parallel, serial,
      console, channel) describes how the device is presented to the guest. The
      guest interface is configured by the <code>target</code> element.
    </p>

    <p>
      The interface presented to the host is given in the <code>type</code>
      attribute of the top-level element. The host interface is
      configured by the <code>source</code> element.
    </p>

    <p>
      Each character device element has an optional
      sub-element <code>&lt;address&gt;</code> which can tie the
      device to a
      particular <a href="#elementsControllers">controller</a> or PCI
      slot.
    </p>

    <h5><a name="elementsCharGuestInterface">Guest interface</a></h5>

    <p>
      A character device presents itself to the guest as one of the following
      types.
    </p>

    <h6><a name="elementCharParallel">Parallel port</a></h6>

<pre>
  ...
  &lt;devices&gt;
    &lt;parallel type='pty'&gt;
      &lt;source path='/dev/pts/2'/&gt;
      &lt;target port='0'/&gt;
    &lt;/parallel&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      <code>target</code> can have a <code>port</code> attribute, which
      specifies the port number. Ports are numbered starting from 0. There are
      usually 0, 1 or 2 parallel ports.
    </p>

    <h6><a name="elementCharSerial">Serial port</a></h6>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type='pty'&gt;
      &lt;source path='/dev/pts/3'/&gt;
      &lt;target port='0'/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      <code>target</code> can have a <code>port</code> attribute, which
      specifies the port number. Ports are numbered starting from 0. There are
      usually 0, 1 or 2 serial ports.
    </p>

    <h6><a name="elementCharConsole">Console</a></h6>

    <p>
      This represents the primary console. This can be the paravirtualized
      console with Xen guests, virtio console for QEMU/KVM, or duplicates
      the primary serial port for fully virtualized guests without a
      paravirtualized console.
    </p>

    <p>
      A virtio console device is exposed in the
      guest as /dev/hvc[0-7] (for more information, see
      <a href="http://fedoraproject.org/wiki/Features/VirtioSerial">http://fedoraproject.org/wiki/Features/VirtioSerial</a>)
      <span class="since">Since 0.8.3</span>
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;console type='pty'&gt;
      &lt;source path='/dev/pts/4'/&gt;
      &lt;target port='0'/&gt;
    &lt;/console&gt;

    &lt;!-- KVM virtio console --&gt;
    &lt;console type='pty'&gt;
      &lt;source path='/dev/pts/5'/&gt;
      &lt;target type='virtio' port='0'/&gt;
    &lt;/console&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      If the console is presented as a serial port, the <code>target</code>
      element has the same attributes as for a serial port. There is usually
      only 1 console.
    </p>

    <h6><a name="elementCharChannel">Channel</a></h6>

    <p>
      This represents a private communication channel between the host and the
      guest.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;channel type='unix'&gt;
      &lt;source mode='bind' path='/tmp/guestfwd'/&gt;
      &lt;target type='guestfwd' address='10.0.2.1' port='4600'/&gt;
    &lt;/channel&gt;

    &lt;!-- KVM virtio channel --&gt;
    &lt;channel type='pty'&gt;
      &lt;target type='virtio' name='arbitrary.virtio.serial.port.name'/&gt;
    &lt;/channel&gt;
    &lt;channel type='spicevmc'&gt;
      &lt;target type='virtio' name='com.redhat.spice.0'/&gt;
    &lt;/channel&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      This can be implemented in a variety of ways. The specific type of
      channel is given in the <code>type</code> attribute of the
      <code>target</code> element. Different channel types have different
      <code>target</code> attributes.
    </p>

    <dl>
      <dt><code>guestfwd</code></dt>
      <dd>TCP traffic sent by the guest to a given IP address and port is
        forwarded to the channel device on the host. The <code>target</code>
        element must have <code>address</code> and <code>port</code> attributes.
        <span class="since">Since 0.7.3</span></dd>

      <dt><code>virtio</code></dt>
      <dd>Paravirtualized virtio channel. Channel is exposed in the guest under
        /dev/vport*, and if the optional element <code>name</code> is specified,
        /dev/virtio-ports/$name (for more info, please see
        <a href="http://fedoraproject.org/wiki/Features/VirtioSerial">http://fedoraproject.org/wiki/Features/VirtioSerial</a>). The
        optional element <code>address</code> can tie the channel to a
        particular <code>type='virtio-serial'</code> controller.
        <span class="since">Since 0.7.7</span></dd>

      <dt><code>spicevmc</code></dt>
      <dd>Paravirtualized SPICE channel. The domain must also have a
        SPICE server as a <a href="#elementsGraphics">graphics
        device</a>, at which point the host piggy-backs messages
        across the <code>main</code> channel.  The <code>target</code>
        element must be present, with
        attribute <code>type='virtio'</code>; an optional
        attribute <code>name</code> controls how the guest will have
        access to the channel, and defaults
        to <code>name='com.redhat.spice.0'</code>.  The
        optional <code>address</code> element can tie the channel to a
        particular <code>type='virtio-serial'</code> controller.
        <span class="since">Since 0.8.8</span></dd>
    </dl>

    <h5><a name="elementsCharHostInterface">Host interface</a></h5>

    <p>
      A character device presents itself to the host as one of the following
      types.
    </p>

    <h6><a name="elementsCharSTDIO">Domain logfile</a></h6>

    <p>
      This disables all input on the character device, and sends output
      into the virtual machine's logfile
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;console type='stdio'&gt;
      &lt;target port='1'&gt;
    &lt;/console&gt;
  &lt;/devices&gt;
  ...</pre>


    <h6><a name="elementsCharFle">Device logfile</a></h6>

    <p>
      A file is opened and all data sent to the character
      device is written to the file.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="file"&gt;
      &lt;source path="/var/log/vm/vm-serial.log"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharVC">Virtual console</a></h6>

    <p>
      Connects the character device to the graphical framebuffer in
      a virtual console. This is typically accessed via a special
      hotkey sequence such as "ctrl+alt+3"
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type='vc'&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharNull">Null device</a></h6>

    <p>
      Connects the character device to the void. No data is ever
      provided to the input. All data written is discarded.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type='null'&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharPTY">Pseudo TTY</a></h6>

    <p>
      A Pseudo TTY is allocated using /dev/ptmx. A suitable client
      such as 'virsh console' can connect to interact with the
      serial port locally.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="pty"&gt;
      &lt;source path="/dev/pts/3"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      NB special case if &lt;console type='pty'&gt;, then the TTY
      path is also duplicated as an attribute tty='/dev/pts/3'
      on the top level &lt;console&gt; tag. This provides compat
      with existing syntax for &lt;console&gt; tags.
    </p>

    <h6><a name="elementsCharHost">Host device proxy</a></h6>

    <p>
      The character device is passed through to the underlying
      physical character device. The device types must match,
      eg the emulated serial port should only be connected to
      a host serial port - don't connect a serial port to a parallel
      port.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="dev"&gt;
      &lt;source path="/dev/ttyS0"/&gt;
      &lt;target port="1"/&gt;
  &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharPipe">Named pipe</a></h6>

    <p>
      The character device writes output to a named pipe. See pipe(7) for
      more info.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="pipe"&gt;
      &lt;source path="/tmp/mypipe"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharTCP">TCP client/server</a></h6>

    <p>
      The character device acts as a TCP client connecting to a
      remote server.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="tcp"&gt;
      &lt;source mode="connect" host="0.0.0.0" service="2445"/&gt;
      &lt;protocol type="raw"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
   ...</pre>

    <p>
      Or as a TCP server waiting for a client connection.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="tcp"&gt;
      &lt;source mode="bind" host="127.0.0.1" service="2445"/&gt;
      &lt;protocol type="raw"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      Alternatively you can use <code>telnet</code> instead
      of <code>raw</code> TCP.  <span class="since">Since 0.8.5</span>
      you can also use <code>telnets</code>
      (secure telnet) and <code>tls</code>.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="tcp"&gt;
      &lt;source mode="connect" host="0.0.0.0" service="2445"/&gt;
      &lt;protocol type="telnet"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
    ...
    &lt;serial type="tcp"&gt;
      &lt;source mode="bind" host="127.0.0.1" service="2445"/&gt;
      &lt;protocol type="telnet"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharUDP">UDP network console</a></h6>

    <p>
      The character device acts as a UDP netconsole service,
      sending and receiving packets. This is a lossy service.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="udp"&gt;
      &lt;source mode="bind" host="0.0.0.0" service="2445"/&gt;
      &lt;source mode="connect" host="0.0.0.0" service="2445"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>

    <h6><a name="elementsCharUNIX">UNIX domain socket client/server</a></h6>

    <p>
      The character device acts as a UNIX domain socket server,
      accepting connections from local clients.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;serial type="unix"&gt;
      &lt;source mode="bind" path="/tmp/foo"/&gt;
      &lt;target port="1"/&gt;
    &lt;/serial&gt;
  &lt;/devices&gt;
  ...</pre>


    <h4><a name="elementsSound">Sound devices</a></h4>

    <p>
      A virtual sound card can be attached to the host via the
      <code>sound</code> element. <span class="since">Since 0.4.3</span>
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;sound model='es1370'/&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>sound</code></dt>
      <dd>
        The <code>sound</code> element has one mandatory attribute,
        <code>model</code>, which specifies what real sound device is emulated.
        Valid values are specific to the underlying hypervisor, though typical
        choices are 'es1370', 'sb16', 'ac97', and 'ich6'
        (<span class="since">
         'ac97' only since 0.6.0, 'ich6' only since 0.8.8</span>)
      </dd>
    </dl>

    <p>
      Each <code>sound</code> element has an optional
      sub-element <code>&lt;address&gt;</code> which can tie the
      device to a particular PCI slot.
    </p>

    <h4><a name="elementsWatchdog">Watchdog device</a></h4>

    <p>
      A virtual hardware watchdog device can be added to the guest via
      the <code>watchdog</code> element.
      <span class="since">Since 0.7.3, QEMU and KVM only</span>
    </p>

    <p>
      The watchdog device requires an additional driver and management
      daemon in the guest.  Just enabling the watchdog in the libvirt
      configuration does not do anything useful on its own.
    </p>

    <p>
      Currently libvirt does not support notification when the
      watchdog fires.  This feature is planned for a future version of
      libvirt.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;watchdog model='i6300esb'/&gt;
  &lt;/devices&gt;
  ...</pre>

<pre>
  ...
  &lt;devices&gt;
    &lt;watchdog model='i6300esb' action='poweroff'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</pre>

    <dl>
      <dt><code>model</code></dt>
      <dd>
        <p>
        The required <code>model</code> attribute specifies what real
        watchdog device is emulated.  Valid values are specific to the
        underlying hypervisor.
        </p>
        <p>
        QEMU and KVM support:
        </p>
        <ul>
          <li> 'i6300esb' &mdash; the recommended device,
            emulating a PCI Intel 6300ESB </li>
          <li> 'ib700' &mdash; emulating an ISA iBase IB700 </li>
        </ul>
      </dd>
      <dt><code>action</code></dt>
      <dd>
        <p>
        The optional <code>action</code> attribute describes what
        action to take when the watchdog expires.  Valid values are
        specific to the underlying hypervisor.
        </p>
        <p>
        QEMU and KVM support:
        </p>
        <ul>
          <li>'reset' &mdash; default, forcefully reset the guest</li>
          <li>'shutdown' &mdash; gracefully shutdown the guest
            (not recommended) </li>
          <li>'poweroff' &mdash; forcefully power off the guest</li>
          <li>'pause' &mdash; pause the guest</li>
          <li>'none' &mdash; do nothing</li>
          <li>'dump' &mdash; automatically dump the guest
            <span class="since">Since 0.8.7</span></li>
        </ul>
        <p>
        Note 1: the 'shutdown' action requires that the guest
        is responsive to ACPI signals.  In the sort of situations
        where the watchdog has expired, guests are usually unable
        to respond to ACPI signals.  Therefore using 'shutdown'
        is not recommended.
        </p>
        <p>
        Note 2: the directory to save dump files can be configured
        by <code>auto_dump_path</code> in file /etc/libvirt/qemu.conf.
        </p>
      </dd>
    </dl>

    <h4><a name="elementsMemBalloon">Memory balloon device</a></h4>

    <p>
      A virtual memory balloon device is added to all Xen and KVM/QEMU
      guests. It will be seen as <code>memballoon</code> element.
      It will be automatically added when appropriate, so there is no
      need to explicitly add this element in the guest XML unless a
      specific PCI slot needs to be assigned.
      <span class="since">Since 0.8.3, Xen, QEMU and KVM only</span>
      Additionally, <span class="since">since 0.8.4</span>, if the
      memballoon device needs to be explicitly disabled,
      <code>model='none'</code> may be used.
    </p>

    <p>
      Example automatically added device with KVM
    </p>
<pre>
  ...
  &lt;devices&gt;
    &lt;memballoon model='virtio'/&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      Example manually added device with static PCI slot 2 requested
    </p>
<pre>
  ...
  &lt;devices&gt;
    &lt;watchdog model='virtio'/&gt;
    &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/&gt;
  &lt;/devices&gt;
&lt;/domain&gt;</pre>

    <dl>
      <dt><code>model</code></dt>
      <dd>
        <p>
          The required <code>model</code> attribute specifies what type
          of balloon device is provided. Valid values are specific to
          the virtualization platform
        </p>
        <ul>
          <li>'virtio' &mdash; default with QEMU/KVM</li>
          <li>'xen' &mdash; default with Xen</li>
        </ul>
      </dd>
    </dl>

    <h3><a name="seclabel">Security label</a></h3>

    <p>
      The <code>seclabel</code> element allows control over the
      operation of the security drivers. There are two basic
      modes of operation, dynamic where libvirt automatically
      generates a unique security label, or static where the
      application/administrator chooses the labels. With dynamic
      label generation, libvirt will always automatically
      relabel any resources associated with the virtual machine.
      With static label assignment, by default, the administrator
      or application must ensure labels are set correctly on any
      resources, however, automatic relabeling can be enabled
      if desired
    </p>

    <p>
      Valid input XML configurations for the security label
      are:
    </p>

    <pre>
  &lt;seclabel type='dynamic' model='selinux'/&gt;

  &lt;seclabel type='dynamic' model='selinux'&gt;
    &lt;baselabel&gt;system_u:system_r:my_svirt_t:s0&lt;/baselabel&gt;
  &lt;/seclabel&gt;

  &lt;seclabel type='static' model='selinux' relabel='no'&gt;
    &lt;label&gt;system_u:system_r:svirt_t:s0:c392,c662&lt;/label&gt;
  &lt;/seclabel&gt;

  &lt;seclabel type='static' model='selinux' relabel='yes'&gt;
    &lt;label&gt;system_u:system_r:svirt_t:s0:c392,c662&lt;/label&gt;
  &lt;/seclabel&gt;
    </pre>

    <p>
      When viewing the XML for a running guest with automatic
      resource relabeling active, an additional XML element,
      <code>imagelabel</code>, will be included. This is an
      output-only element, so will be ignored in user supplied
      XML documents
    </p>
    <dl>
      <dt><code>type</code></dt>
      <dd>Either <code>static</code> or <code>dynamic</code> to determine
        whether libvirt automatically generates a unique security label
        or not.
      </dd>
      <dt><code>model</code></dt>
      <dd>A valid security model name, matching the currently
        activated security model
      </dd>
      <dt><code>relabel</code></dt>
      <dd>Either <code>yes</code> or <code>no</code>. This must always
        be <code>yes</code> if dynamic label assignment is used. With
        static label assignment it will default to <code>no</code>.
      </dd>
      <dt><code>label</code></dt>
      <dd>If static labelling is used, this must specify the full
        security label to assign to the virtual domain. The format
        of the content depends on the security driver in use
      </dd>
      <dt><code>baselabel</code></dt>
      <dd>If dynamic labelling is used, this can optionally be
        used to specify the base security label. The format
        of the content depends on the security driver in use
      </dd>
      <dt><code>imagelabel</code></dt>
      <dd>This is an output only element, which shows the
        security label used on resources associated with the virtual domain.
        The format of the content depends on the security driver in use
      </dd>
    </dl>

    <h2><a name="examples">Example configs</a></h2>

    <p>
      Example configurations for each driver are provide on the
      driver specific pages listed below
    </p>

    <ul>
      <li><a href="drvxen.html#xmlconfig">Xen examples</a></li>
      <li><a href="drvqemu.html#xmlconfig">QEMU/KVM examples</a></li>
    </ul>
  </body>
</html>
