formatdomain.html.in

<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;title&gt;A short description - title - of the domain&lt;/title&gt;
  &lt;description&gt;Some human readable description&lt;/description&gt;
  &lt;metadata&gt;
    &lt;app1:foo xmlns:app1="http://app1.org/app1/"&gt;..&lt;/app1:foo&gt;
    &lt;app2:bar xmlns:app2="http://app1.org/app2/"&gt;..&lt;/app2:bar&gt;
  &lt;/metadata&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>title</code></dt>
      <dd>The optional element <code>title</code> provides space for a
        short description of the domain. The title should not contain
        any newlines. <span class="since">Since 0.9.10</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>

      <dt><code>metadata</code></dt>
      <dd>The <code>metadata</code> node can be used by applications
        to store custom metadata in the form of XML
        nodes/trees. Applications must use custom namespaces on their
        XML nodes/trees, with only one top-level element per namespace
        (if the application needs structure, they should have
        sub-elements to their namespace
        element). <span class="since">Since 0.9.10</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.
        Multiple devices of the same type are sorted according to their
        targets while preserving the order of buses. After defining the
        domain, its XML configuration returned by libvirt (through
        virDomainGetXMLDesc) lists devices in the sorted order. Once sorted,
        the first device is marked as bootable. Thus, e.g., a domain
        configured to boot from "hd" with vdb, hda, vda, and hdc disks
        assigned to it will boot from vda (the sorted list is vda, vdb, hda,
        hdc). Similar domain with hdc, vda, vdb, and hda disks will boot from
        hda (sorted disks are: hda, hdc, vda, vdb). It can be tricky to
        configure in the desired way, which is why per-device boot elements
        (see <a href="#elementsDisks">disks</a>,
        <a href="#elementsNICS">network interfaces</a>, and
        <a href="#elementsUSB">USB and PCI devices</a> sections below) were
        introduced and they are the preferred way providing full control over
        booting order. The <code>boot</code> element and per-device boot
        elements are mutually exclusive. <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>

    <h4><a name="eleemntsOSContainer">Container boot</a></h4>

    <p>
      When booting a domain using container based virtualization, instead
      of a kernel / boot image, a path to the init binary is required, using
      the <code>init</code> element. By default this will be launched with
      no arguments. To specify the initial argv, use the <code>initarg</code>
      element, repeated as many time as is required. The <code>cmdline</code>
      element, if set will be used to provide an equivalent to <code>/proc/cmdline</code>
      but will not effect init argv.
    </p>

    <pre>
  &lt;os&gt;
    &lt;type arch='x86_64'&gt;exe&lt;/type&gt;
    &lt;init&gt;/bin/systemd&lt;/init&gt;
    &lt;initarg&gt;--unit&lt;/initarg&gt;
    &lt;initarg&gt;emergency.service&lt;/initarg&gt;
  &lt;/os&gt;
    </pre>


    <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 placement='static' 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.  <span class="since">Since
        0.9.11 (QEMU and KVM only), the optional attribute
        <code>placement</code> can be used to indicate the CPU placement
        mode for domain process, its value can be either "static" or
        "auto", defaults to "static" if <code>cpuset</code> is specified,
        "auto" indicates the domain process will be pinned to the advisory
        nodeset from querying numad, and the value of attribute
        <code>cpuset</code> will be overridden by the advisory nodeset
        from numad if it's specified. If both <code>cpuset</code> and
        <code>placement</code> are not specified, or if <code>placement</code>
        is "static", but no <code>cpuset</code> is specified, the domain
        process will be pinned to all the available physical CPUs.
      </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 unit='KiB'&gt;524288&lt;/memory&gt;
  &lt;currentMemory unit='KiB'&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 determined by the optional
        atttribute <code>unit</code>, which defaults to "KiB"
        (kibibytes, 2<sup>10</sup> or blocks of 1024 bytes).  Valid
        units are "b" or "bytes" for bytes, "KB" for kilobytes
        (10<sup>3</sup> or 1,000 bytes), "k" or "KiB" for kibibytes
        (1024 bytes), "MB" for megabytes (10<sup>6</sup> or 1,000,000
        bytes), "M" or "MiB" for mebibytes (2<sup>20</sup> or
        1,048,576 bytes), "GB" for gigabytes (10<sup>9</sup> or
        1,000,000,000 bytes), "G" or "GiB" for gibibytes
        (2<sup>30</sup> or 1,073,741,824 bytes), "TB" for terabytes
        (10<sup>12</sup> or 1,000,000,000,000 bytes), or "T" or "TiB"
        for tebibytes (2<sup>40</sup> or 1,099,511,627,776 bytes).
        However, the value will be rounded up to the nearest kibibyte
        by libvirt, and may be further rounded to the granularity
        supported by the hypervisor.  Some hypervisors also enforce a
        minimum, such as
        4000KiB. <span class='since'><code>unit</code> since
        0.9.11</span></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.
        The <code>unit</code> attribute behaves the same as
        for <code>memory</code>.</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 unit='G'&gt;1&lt;/hard_limit&gt;
    &lt;soft_limit unit='M'&gt;128&lt;/soft_limit&gt;
    &lt;swap_hard_limit unit='G'&gt;2&lt;/swap_hard_limit&gt;
    &lt;min_guarantee unit='bytes'&gt;67108864&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.  For each tunable, it
        is possible to designate which unit the number is in on
        input, using the same values as
        for <code>&lt;memory&gt;</code>.  For backwards
        compatibility, output is always in
        KiB.  <span class='since'><code>unit</code>
        since 0.9.11</span></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 kibibytes (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
        kibibytes (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
        kibibytes (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
        kibibytes (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 specifies 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;device&gt;
      &lt;path&gt;/dev/sda&lt;/path&gt;
      &lt;weight&gt;1000&lt;/weight&gt;
    &lt;/device&gt;
    &lt;device&gt;
      &lt;path&gt;/dev/sdb&lt;/path&gt;
      &lt;weight&gt;500&lt;/weight&gt;
    &lt;/device&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. <span class="since">Since 0.8.8</span></dd>
      <dt><code>weight</code></dt>
      <dd> The optional <code>weight</code> element is the overall I/O
        weight of the guest. The value should be in the range [100,
        1000].</dd>
      <dt><code>device</code></dt>
      <dd>The domain may have multiple <code>device</code> elements
        that further tune the weights for each host block device in
        use by the domain.  Note that
        multiple <a href="#elementsDisks">guest disks</a> can share a
        single host block device, if they are backed by files within
        the same host file system, which is why this tuning parameter
        is at the global domain level rather than associated with each
        guest disk device (contrast this to
        the <a href="#elementsDisks"><code>&lt;iotune&gt;</code></a>
        element which can apply to an
        individual <code>&lt;disk&gt;</code>).
        Each <code>device</code> element has two
        mandatory sub-elements, <code>path</code> describing the
        absolute path of the device, and <code>weight</code> giving
        the relative weight of that device, in the range [100,
        1000].  <span class="since">Since 0.9.8</span></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 fallback='allow'&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>

<pre>
  &lt;cpu mode='host-model'&gt;
    &lt;model fallback='forbid'/&gt;
    &lt;topology sockets='1' cores='2' threads='1'/&gt;
  &lt;/cpu&gt;
  ...</pre>

<pre>
  &lt;cpu mode='host-passthrough'/&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>.

        <span class="since">Since 0.9.10</span>, an optional <code>mode</code>
        attribute may be used to make it easier to configure a guest CPU to be
        as close to host CPU as possible. Possible values for the
        <code>mode</code> attribute are:

        <dl>
          <dt><code>custom</code></dt>
          <dd>In this mode, the <code>cpu</code> element describes the CPU
          that should be presented to the guest. This is the default when no
          <code>mode</code> attribute is specified. This mode makes it so that
          a persistent guest will see the same hardware no matter what host
          the guest is booted on.</dd>
          <dt><code>host-model</code></dt>
          <dd>The <code>host-model</code> mode is essentially a shortcut to
          copying host CPU definition from capabilities XML into domain XML.
          Since the CPU definition is copied just before starting a domain,
          exactly the same XML can be used on different hosts while still
          providing the best guest CPU each host supports. Neither
          <code>match</code> attribute nor any <code>feature</code> elements
          can be used in this mode. Specifying CPU model is not supported
          either, but <code>model</code>'s <code>fallback</code> attribute may
          still be used. Libvirt does not model every aspect of each CPU so
          the guest CPU will not match the host CPU exactly. On the other
          hand, the ABI provided to the guest is reproducible. During
          migration, complete CPU model definition is transferred to the
          destination host so the migrated guest will see exactly the same CPU
          model even if the destination host contains more capable CPUs for
          the running instance of the guest; but shutting down and restarting
          the guest may present different hardware to the guest according to
          the capabilities of the new host.</dd>
          <dt><code>host-passthrough</code></dt>
          <dd>With this mode, the CPU visible to the guest should be exactly
          the same as the host CPU even in the aspects that libvirt does not
          understand. Though the downside of this mode is that the guest
          environment cannot be reproduced on different hardware. Thus, if you
          hit any bugs, you are on your own. Neither <code>model</code> nor
          <code>feature</code> elements are allowed in this mode.</dd>
        </dl>

        In both <code>host-model</code> and <code>host-passthrough</code>
        mode, the real (approximate in <code>host-passthrough</code> mode) CPU
        definition which would be used on current host can be determined by
        specifying <code>VIR_DOMAIN_XML_UPDATE_CPU</code> flag when calling
        <code>virDomainGetXMLDesc</code> API. When running a guest that might
        be prone to operating system reactivation when presented with
        different hardware, and which will be migrated between hosts with
        different capabilities, you can use this output to rewrite XML to the
        <code>custom</code> mode for more robust migration.
      </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. If a hypervisor is not able to use the
        exact CPU model, libvirt automatically falls back to a closest model
        supported by the hypervisor while maintaining the list of CPU
        features. <span class="since">Since 0.9.10</span>, an optional
        <code>fallback</code> attribute can be used to forbid this behavior,
        in which case an attempt to start a domain requesting an unsupported
        CPU model will fail. Supported values for <code>fallback</code>
        attribute are: <code>allow</code> (this is the default), and
        <code>forbid</code>.</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>

    <p>
      Guest NUMA topology can be specifed using the <code>numa</code> element.
      <span class="since">Since 0.9.8</span>
    </p>

<pre>
  ...
  &lt;cpu&gt;
    ...
    &lt;numa&gt;
      &lt;cell cpus='0-3' memory='512000'/&gt;
      &lt;cell cpus='4-7' memory='512000'/&gt;
    &lt;/numa&gt;
    ...
  &lt;/cpu&gt;
  ...</pre>

    <p>
      Each <code>cell</code> element specifies a NUMA cell or a NUMA node.
      <code>cpus</code> specifies the CPU or range of CPUs that are part of
      the node. <code>memory</code> specifies the node memory in kibibytes
      (i.e. blocks of 1024 bytes). Each cell or node is assigned cellid
      or nodeid in the increasing order starting from 0.
    </p>

    <p>
      This guest NUMA specification is currently available only for QEMU/KVM.
    </p>

    <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;privnet/&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>
      <dt><code>viridian</code></dt>
      <dd>Enable Viridian hypervisor extensions for paravirtualizing
        guest operating systems
      </dd>
      <dt><code>privnet</code></dt>
      <dd>Always create a private network namespace. This is
        automatically set if any interface devices are defined.
        This feature is only relevant for container based
        virtualization drivers, such as LXC.
      </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="delay"/&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 and 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", "hpet",
            "kvmclock", "pit", "rtc", 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>
            <p>
            The <code>tickpolicy</code> attribute determines what
            happens whens QEMU misses a deadline for injecting a
            tick to the guest:
            </p>
            <dl>
              <dt><code>delay</code></dt>
              <dd>Continue to deliver ticks at the normal rate.
                The guest time will be delayed due to the late
                tick</dd>
              <dt><code>catchup</code></dt>
              <dd>Deliver ticks at a higher rate to catch up
                with the missed tick. The guest time should
                not be delayed once catchup is complete.</dd>
              <dt><code>merge</code></dt>
              <dd>Merge the missed tick(s) into one tick and
                inject. The guest time may be delayed, depending
                on how the OS reacts to the merging of ticks</dd>
              <dt><code>discard</code></dt>
              <dd>Throw away the missed tick(s) and continue
                with future injection normally. The guest time
                may be delayed, unless the OS has explicit
                handling of lost ticks</dd>
            </dl>
            <p>If the policy is "catchup", there can be further details in
            the <code>catchup</code> sub-element.</p>
            <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>
            <p>
              Note that hypervisors are not required to support all policies across all time sources
            </p>
          </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' startupPolicy='optional'&gt;
        &lt;seclabel relabel='no'/&gt;
      &lt;/source&gt;
      &lt;target dev='hda' bus='ide'/&gt;
      &lt;iotune&gt;
        &lt;total_bytes_sec&gt;10000000&lt;/total_bytes_sec&gt;
        &lt;read_iops_sec&gt;400000&lt;/read_iops_sec&gt;
        &lt;write_iops_sec&gt;100000&lt;/write_iops_sec&gt;
      &lt;/iotune&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='network'&gt;
      &lt;driver name="qemu" type="raw"/&gt;
      &lt;source protocol="rbd" name="image_name2"&gt;
        &lt;host name="hostname" port="7000"/&gt;
      &lt;/source&gt;
      &lt;target dev="hdd" bus="ide"/&gt;
      &lt;auth username='myuser'&gt;
        &lt;secret type='ceph' usage='mypassid'/&gt;
      &lt;/auth&gt;
    &lt;/disk&gt;
    &lt;disk type='block' device='cdrom'&gt;
      &lt;driver name='qemu' type='raw'/&gt;
      &lt;target dev='hdc' bus='ide' tray='open'/&gt;
      &lt;readonly/&gt;
    &lt;/disk&gt;
    &lt;disk type='block' device='lun'&gt;
      &lt;driver name='qemu' type='raw'/&gt;
      &lt;source dev='/dev/sda'/&gt;
      &lt;target dev='sda' bus='scsi'/&gt;
      &lt;address type='drive' controller='0' bus='0' target='3' unit='0'/&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", "cdrom", and "lun", defaulting to
        "disk". "lun" (<span class="since">since 0.9.10</span>) is only
        valid when type is "block" and the target element's "bus"
        attribute is "virtio", and behaves identically to "disk",
        except that generic SCSI commands from the guest are accepted
        and passed through to the physical device
        - also note that device='lun' will only be recognized for
        actual raw devices, never for individual partitions or LVM
        partitions (in those cases, the kernel will reject the generic
        SCSI commands, making it identical to device='disk').
        The optional <code>rawio</code> attribute
        (<span class="since">since 0.9.10</span>) indicates whether
        the disk is needs rawio capability; valid settings are "yes"
        or "no" (default is "no"). If any one disk in a domain has
        rawio='yes', rawio capability will be enabled for all disks in
        the domain (because, in the case of QEMU, this capability can
        only be set on a per-process basis). This attribute is only
        valid when device is "lun".
        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. With both "file" and "block", an optional
        sub-element <code>seclabel</code>, <a href="#seclabel">described
        below</a> (and <span class="since">since 0.9.9</span>), can be
        used to override the domain security labeling policy for just
        that source file.  If the disk <code>type</code> is "dir", then the
        <code>dir</code> attribute specifies the fully-qualified path
        to the directory to use 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 will 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; <code>type='dir'</code> since
        0.7.5; <code>type='network'</code> since 0.8.7</span><br/>
        For a "file" disk type which represents a cdrom or floppy
        (the <code>device</code> attribute), it is possible to define
        policy what to do with the disk if the source file is not accessible.
        This is done by the <code>startupPolicy</code> attribute, accepting
        these values:
        <table class="top_table">
          <tr>
            <td> mandatory </td>
            <td> fail if missing for any reason (the default) </td>
          </tr>
          <tr>
            <td> requisite </td>
            <td> fail if missing on boot up,
                 drop if missing on migrate/restore/revert </td>
          </tr>
          <tr>
            <td> optional </td>
            <td> drop if missing at any start attempt </td>
          </tr>
        </table>
        <span class="since">Since 0.9.7</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", "usb" or "sata". 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. The optional
        attribute <code>tray</code> indicates the tray status of the
        removable disks (i.e. CDROM or Floppy disk), the value can be either
        "open" or "closed", defaults to "closed". NB, the value of
        <code>tray</code> could be updated while the domain is running.
        <span class="since">Since 0.0.3; <code>bus</code> attribute since 0.4.3;
        <code>tray</code> attribute since 0.9.11; "usb" attribute value since
        after 0.4.4; "sata" attribute value since 0.9.7</span>
      </dd>
      <dt><code>iotune</code></dt>
      <dd>The optional <code>iotune</code> element provides the
        ability to provide additional per-device I/O tuning, with
        values that can vary for each device (contrast this to
        the <a href="#elementsBlockTuning"><code>&lt;blkiotune&gt;</code></a>
        element, which applies globally to the domain).  Currently,
        the only tuning available is Block I/O throttling for qemu.
        This element has optional sub-elements; any sub-element not
        specified or given with a value of 0 implies no
        limit.  <span class="since">Since 0.9.8</span>
        <dl>
          <dt><code>total_bytes_sec</code></dt>
          <dd>The optional <code>total_bytes_sec</code> element is the
            total throughput limit in bytes per second.  This cannot
            appear with <code>read_bytes_sec</code>
            or <code>write_bytes_sec</code>.</dd>
          <dt><code>read_bytes_sec</code></dt>
          <dd>The optional <code>read_bytes_sec</code> element is the
            read throughput limit in bytes per second.</dd>
          <dt><code>write_bytes_sec</code></dt>
          <dd>The optional <code>write_bytes_sec</code> element is the
            write throughput limit in bytes per second.</dd>
          <dt><code>total_iops_sec</code></dt>
          <dd>The optional <code>total_iops_sec</code> element is the
            total I/O operations per second.  This cannot
            appear with <code>read_iops_sec</code>
            or <code>write_iops_sec</code>.</dd>
          <dt><code>read_iops_sec</code></dt>
          <dd>The optional <code>read_iops_sec</code> element is the
            read I/O operations per second.</dd>
          <dt><code>write_iops_sec</code></dt>
          <dd>The optional <code>write_iops_sec</code> element is the
            write I/O operations per second.</dd>
        </dl>
      <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", "directsync" (like
            "writethrough", but it bypasses the host page cache) and
            "unsafe" (host may cache all disk io, and sync requests from
            guest are ignored).
            <span class="since">
              Since 0.6.0,
              "directsync" since 0.9.5,
              "unsafe" since 0.9.7
            </span>
          </li>
          <li>
            The optional <code>error_policy</code> attribute controls
            how the hypervisor will behave on a disk read or write
            error, possible values are "stop", "report", "ignore", and
            "enospace".<span class="since">Since 0.8.0, "report" since
            0.9.7</span> The default setting of error_policy is "report".
            There is also an
            optional <code>rerror_policy</code> that controls behavior
            for read errors only. <span class="since">Since
            0.9.7</span>. If no rerror_policy is given, error_policy
            is used for both read and write errors. If rerror_policy
            is given, it overrides the <code>error_policy</code> for
            read errors. Also note that "enospace" is not a valid
            policy for read errors, so if <code>error_policy</code> is
            set to "enospace" and no <code>rerror_policy</code> is
            given, the read error policy will be left at its default,
            which is "report".
          </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>
          <li>
            The optional <code>copy_on_read</code> attribute controls
            wether to copy read backing file into the image file. The
            value can be either "on" or "off".
            Copy-on-read avoids accessing the same backing file sectors
            repeatedly and is useful when the backing file is over a slow
            network. By default copy-on-read is off.
            <span class='since'>Since 0.9.10 (QEMU and KVM only)</span>
          </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
        optional <code>domain</code> and <code>multifunction</code>.
        Multifunction defaults to 'off'; any other value requires
        QEMU 0.1.3 and <span class="since">libvirt 0.9.7</span>.  For a
        "drive" controller, additional attributes
        <code>controller</code>, <code>bus</code>, <code>target</code>
        (<span class="since">libvirt 0.9.11</span>), and <code>unit</code>
        are available, each defaulting to 0.
      </dd>
      <dt><code>auth</code></dt>
      <dd>If present, the <code>auth</code> element provides the
        authentication credentials needed to access the source.  It
        includes a mandatory attribute <code>username</code>, which
        identifies the username to use during authentication, as well
        as a sub-element <code>secret</code> with mandatory
        attribute <code>type</code>, to tie back to
        a <a href="formatsecret.html">libvirt secret object</a> that
        holds the actual password or other credentials (the domain XML
        intentionally does not expose the password, only the reference
        to the object that does manage the password).  For now, the
        only known secret <code>type</code> is "ceph", for Ceph RBD
        network sources, and requires either an
        attribute <code>uuid</code> with the UUID of the Ceph secret
        object, or an attribute <code>usage</code> with the name
        associated with the Ceph secret
        object.  <span class="since">libvirt 0.9.7</span>
      </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;driver type='path' wrpolicy='immediate'/&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.
        This mode also has an optional
        sub-element <code>driver</code>, with an
        attribute <code>type='path'</code>
        or <code>type='handle'</code> <span class="since">(since
        0.9.7)</span>. The driver block has an optional attribute
        <code>wrpolicy</code> that further controls interaction with
        the host page cache; omitting the attribute gives default behavior,
        while the value <code>immediate</code> means that a host writeback
        is immediately triggered for all pages touched during a guest file
        write operation <span class="since">(since 0.9.10)</span>.
        </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>
        A host block device to mount in the guest. The filesystem
        format will be autodetected. Only used by LXC driver
        <span class="since">(since 0.9.5)</span>.
        </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>
        Enables exporting filesytem as a readonly mount for guest, by
        default read-write access is given (currently only works for
        QEMU/KVM driver).
      </dd>
    </dl>

    <h4><a name="elementsAddress">Device Addresses</a></h4>

    <p>
      Many devices have an optional <code>&lt;address&gt;</code>
      sub-element to describe where the device is placed on the
      virtual bus presented to the guest.  If an address (or any
      optional attribute within an address) is omitted on
      input, libvirt will generate an appropriate address; but an
      explicit address is required if more control over layout is
      required.  See below for device examples including an address
      element.
    </p>

    <p>
      Every address has a mandatory attribute <code>type</code> that
      describes which bus the device is on.  The choice of which
      address to use for a given device is constrained in part by the
      device and the architecture of the guest.  For example,
      a <code>&lt;disk&gt;</code> device
      uses <code>type='disk'</code>, while
      a <code>&lt;console&gt;</code> device would
      use <code>type='pci'</code> on i686 or x86_64 guests,
      or <code>type='spapr-vio'</code> on PowerPC64 pseries guests.
      Each address type has further optional attributes that control
      where on the bus the device will be placed:
    </p>

    <dl>
      <dt><code>type='pci'</code></dt>
      <dd>PCI addresses have the following additional
        attributes: <code>domain</code> (a 2-byte hex integer, not
        currently used by qemu), <code>bus</code> (a hex value between
        0 and 0xff, inclusive), <code>slot</code> (a hex value between
        0x0 and 0x1f, inclusive), and <code>function</code> (a value
        between 0 and 7, inclusive).  Also available is
        the <code>multifunction</code> attribute, which controls
        turning on the multifunction bit for a particular
        slot/function in the PCI control register
        (<span class="since">since 0.9.7, requires QEMU
        0.13</span>). <code>multifunction</code> defaults to 'off',
        but should be set to 'on' for function 0 of a slot that will
        have multiple functions used.
      </dd>
      <dt><code>type='drive'</code></dt>
      <dd>Drive addresses have the following additional
        attributes: <code>controller</code> (a 2-digit controller
        number), <code>bus</code> (a 2-digit bus number),
        <code>target</code> (a 2-digit bus number),
        and <code>unit</code> (a 2-digit unit number on the bus).
      </dd>
      <dt><code>type='virtio-serial'</code></dt>
      <dd>Each virtio-serial address has the following additional
        attributes: <code>controller</code> (a 2-digit controller
        number), <code>bus</code> (a 2-digit bus number),
        and <code>slot</code> (a 2-digit slot within the bus).
      </dd>
      <dt><code>type='ccid'</code></dt>
      <dd>A CCID address, for smart-cards, has the following
        additional attributes: <code>bus</code> (a 2-digit bus
        number), and <code>slot</code> attribute (a 2-digit slot
        within the bus).  <span class="since">Since 0.8.8.</span>
      <dt><code>type='usb'</code></dt>
      <dd>USB addresses have the following additional
        attributes: <code>bus</code> (a hex value between 0 and 0xfff,
        inclusive), and <code>port</code> (a dotted notation of up to
        four octets, such as 1.2 or 2.1.3.1).
      </dd>
      <dt><code>type='spapr-vio'</code></dt>
      <dd>On PowerPC pseries guests, devices can be assigned to the
        SPAPR-VIO bus.  It has a flat 64-bit address space; by
        convention, devices are generally assigned at a non-zero
        multiple of 0x1000, but other addresses are valid and
        permitted by libvirt.  Each address has the following
        additional attribute: <code>reg</code> (the hex value address
        of the starting register).  <span class="since">Since
        0.9.9.</span>
      </dd>
    </dl>

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

    <p>
      Depending on the guest architecture, some device busses can
      appear more than once, with a group of virtual devices tied to a
      virtual controller.  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",
      "ibmvscsi", "lsilogic", "lsias1068", "virtio-scsi" 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".  The PowerPC64 "spapr-vio"
      addresses do not have an associated controller.
    </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 <a href="#elementsAddress">given above</a>.
    </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' multifunction='on'/&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;rom bar='on' file='/etc/fake/boot.bin'/&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, and reattached to the host after the guest exits.
        If <code>managed</code> is omitted or "no", and for USB
        devices, the user is responsible to
        call <code>virNodeDeviceDettach</code> (or <code>virsh
        nodedev-dettach</code>) before starting the guest or
        hot-plugging the device,
        and <code>virNodeDeviceReAttach</code> (or <code>virsh
        nodedev-reattach</code>) after hot-unplug or stopping 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>rom</code></dt>
      <dd>The <code>rom</code> element is used to change how a PCI
        device's ROM is presented to the guest. The optional <code>bar</code>
        attribute can be set to "on" or "off", and determines whether
        or not the device's ROM will be visible in the guest's memory
        map. (In PCI documentation, the "rombar" setting controls the
        presence of the Base Address Register for the ROM). If no rom
        bar is specified, the qemu default will be used (older
        versions of qemu used a default of "off", while newer qemus
        have a default of "on"). <span class="since">Since
        0.9.7 (QEMU and KVM only)</span>. The optional
        <code>file</code> attribute is used to point to a binary file
        to be presented to the guest as the device's ROM BIOS. This
        can be useful, for example, to provide a PXE boot ROM for a
        virtual function of an sr-iov capable ethernet device (which
        has no boot ROMs for the VFs).
        <span class="since">Since 0.9.10 (QEMU and KVM only)</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>. <a href="#elementsAddress">See above</a> for
      more details on the address element.
    </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.</dd>

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

    <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, <a href="#elementsAddress">documented above</a>.
      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;rom bar='off'/&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>
      as <a href="#elementsAddress">documented above</a>.
    </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="elementsNICSHostdev">PCI Passthrough</a></h5>

    <p>
      A PCI network device (specified by the &lt;source&gt; element)
      is directly assigned to the guest using generic device
      passthrough, after first optionally setting the device's MAC
      address to the configured value, and associating the device with
      an 802.1Qgh capable switch using an optionally specified
      %lt;virtualport%gt; element (see the examples of virtualport
      given above for type='direct' network devices). Note that - due
      to limitations in standard single-port PCI ethernet card driver
      design - only SR-IOV (Single Root I/O Virtualization) virtual
      function (VF) devices can be assigned in this manner; to assign
      a standard single-port PCI or PCIe ethernet card to a guest, use
      the traditional &lt;hostdev&gt; device definition and
      <span class="since">Since 0.9.11</span>
    </p>

    <p>
      Note that this "intelligent passthrough" of network devices is
      very similar to the functionality of a standard &lt;hostdev&gt;
      device, the difference being that this method allows specifying
      a MAC address and &lt;virtualport&gt; for the passed-through
      device. If these capabilities are not required, if you have a
      standard single-port PCI, PCIe, or USB network card that doesn't
      support SR-IOV (and hence would anyway lose the configured MAC
      address during reset after being assigned to the guest domain),
      or if you are using a version of libvirt older than 0.9.11, you
      should use standard &lt;hostdev&gt; to assign the device to the
      guest instead of &lt;interface type='hostdev'/&gt;.
    </p>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='hostdev'&gt;
      &lt;source&gt;
        &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/&gt;
      &lt;/source&gt;
      &lt;mac address='52:54:00:6d:90:02'&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;mac address='52:54:00:6d:90:01'&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;mac address='52:54:00:22:c9:42'&gt;
      &lt;source address='192.168.0.1' port='5558'/&gt;
    &lt;/interface&gt;
    ...
    &lt;interface type='client'&gt;
      &lt;mac address='52:54:00:8b:c9:51'&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 a specific NIC to
      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="elementsNICSROM">Interface ROM BIOS configuration</a></h5>

<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet1'/&gt;
      <b>&lt;rom bar='on' file='/etc/fake/boot.bin'/&gt;</b>
    &lt;/interface&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>
      For hypervisors which support this, you can change how a PCI Network
      device's ROM is presented to the guest. The <code>bar</code>
      attribute can be set to "on" or "off", and determines whether
      or not the device's ROM will be visible in the guest's memory
      map. (In PCI documentation, the "rombar" setting controls the
      presence of the Base Address Register for the ROM). If no rom
      bar is specified, the qemu default will be used (older
      versions of qemu used a default of "off", while newer qemus
      have a default of "on").
      The optional <code>file</code> attribute is used to point to a
      binary file to be presented to the guest as the device's ROM
      BIOS. This can be useful to provide an alternative boot ROM for a
      network device.
      <span class="since">Since 0.9.10 (QEMU and KVM only)</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>

    <h5><a name="elementLink">Modifying virtual link state</a></h5>
<pre>
  ...
  &lt;devices&gt;
    &lt;interface type='network'&gt;
      &lt;source network='default'/&gt;
      &lt;target dev='vnet0'/&gt;
      <b>&lt;link state='down'/&gt;</b>
    &lt;/interface&gt;
  &lt;devices&gt;
  ...</pre>

    <p>
      This element provides means of setting state of the virtual network link.
      Possible values for attribute <code>state</code> are <code>up</code> and
      <code>down</code>. If <code>down</code> is specified as the value, the interface
      behaves as if it had the network cable disconnected. Default behavior if this
      element is unspecified is to have the link state <code>up</code>.
      <span class="since">Since 0.9.5</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, <a href="#elementsAddress">documented above</a>.
    </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>
      with <code>type='usb'</code>which can tie the device to a
      particular controller, <a href="#elementsAddress">documented
      above</a>.
    </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;mouse mode='client'/&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 its <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>
            <p>
              Mouse mode is set by the <code>mouse</code> element,
              setting its <code>mode</code> attribute to one of
              <code>server</code> or <code>client</code> ,
              <span class="since">since 0.9.11</span>. If no mode is
              specified, the qemu default will be used (client mode).
            </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 container for describing
        video devices. For backwards compatibility, 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 kibibytes
        (blocks of 1024 bytes) 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>
      The console element is used to represent interactive consoles. Depending
      on the type of guest in use, the consoles might be paravirtualized devices,
      or they might be a clone of a serial device, according to the following
      rules:
    </p>

    <ul>
      <li>If no <code>targetType</code> attribue is set, then the default
        device type is according to the hypervisor's rules. The default
        type will be added when re-querying the XML fed into libvirt.
        For fully virtualized guests, the default device type will usually
        be a serial port.</li>
      <li>If the <code>targetType</code> attribute is <code>serial</code>,
        then if no <code>&lt;serial&gt;</code> element exists, the console
        element will be copied to the serial element. If a <code>&lt;serial&gt;</code>
        element does already exist, the console element will be ignored.</li>
      <li>If the <code>targetType</code> attribute is not <code>serial</code>,
        it will be treated normally.</li>
      <li>Only the first <code>console</code> element may use a <code>targetType</code>
        of <code>serial</code>. Secondary consoles must all be paravirtualized.
      </li>
    </ul>

    <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='unix'&gt;
      &lt;source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/&gt;
      &lt;target type='virtio' name='org.qemu.guest_agent.0'/&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, <a href="#elementsAddress">documented above</a>.
        With qemu, if <code>name</code> is "org.qemu.guest_agent.0",
        then libvirt can interact with a guest agent installed in the
        guest, for actions such as guest shutdown or file system quiescing.
        <span class="since">Since 0.7.7, guest agent interaction
        since 0.9.10</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, <a href="#elementsAddress">documented above</a>.
    </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 three basic
      modes of operation, 'dynamic' where libvirt automatically
      generates a unique security label, 'static' where the
      application/administrator chooses the labels, or 'none'
      where confinement is disabled. 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.  <span class="since">'dynamic' since 0.6.1, 'static'
      since 0.6.2, and 'none' since 0.9.10.</span>
    </p>

    <p>
      Valid input XML configurations for the top-level 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;

  &lt;seclabel type='none'/&gt;
    </pre>

    <p>
      If no 'type' attribute is provided in the input XML, then
      the security driver default setting will be used, which
      may be either 'none' or 'dynamic'. If a 'baselabel' is set
      but no 'type' is set, then the type is presumed to be 'dynamic'
    </p>

    <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>, <code>dynamic</code> or <code>none</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>

    <p>When relabeling is in effect, it is also possible to fine-tune
      the labeling done for specific source file names, by either
      disabling the labeling (useful if the file lives on NFS or other
      file system that lacks security labeling) or requesting an
      alternate label (useful when a management application creates a
      special label to allow sharing of some, but not all, resources
      between domains), <span class="since">since 0.9.9</span>.  When
      a <code>seclabel</code> element is attached to a specific path
      rather than the top-level domain assignment, only the
      attribute <code>relabel</code> or the
      sub-element <code>label</code> are supported.
    </p>

    <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>