formatcaps.html.in

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    <h1>Driver capabilities XML format</h1>

        <p>As new virtualization engine support gets added to libvirt, and to handle
cases like QEmu supporting a variety of emulations, a query interface has
been added in 0.2.1 allowing to list the set of supported virtualization
capabilities on the host:</p>
        <pre>    char * virConnectGetCapabilities (virConnectPtr conn);</pre>
        <p>The value returned is an XML document listing the virtualization
capabilities of the host and virtualization engine to which
<code>@conn</code> is connected. One can test it using <code>virsh</code>
command line tool command '<code>capabilities</code>', it dumps the XML
associated to the current connection. For example in the case of a 64 bits
machine with hardware virtualization capabilities enabled in the chip and
BIOS you will see</p>
        <pre>&lt;capabilities&gt;
  <span style="color: #E50000">&lt;host&gt;
    &lt;cpu&gt;
      &lt;arch&gt;x86_64&lt;/arch&gt;
      &lt;features&gt;
        &lt;vmx/&gt;
      &lt;/features&gt;
      &lt;model&gt;core2duo&lt;/model&gt;
      &lt;vendor&gt;Intel&lt;/vendor&gt;
      &lt;topology sockets="1" cores="2" threads="1"/&gt;
      &lt;feature name="lahf_lm"/&gt;
      &lt;feature name='xtpr'/&gt;
      ...
    &lt;/cpu&gt;
    &lt;power_management&gt;
      &lt;S3/&gt;
      &lt;S4/&gt;
      &lt;Hybrid-Suspend/&gt;
    &lt;power_management/&gt;
  &lt;/host&gt;</span>

  &lt;!-- xen-3.0-x86_64 --&gt;
  <span style="color: #0000E5">&lt;guest&gt;
    &lt;os_type&gt;xen&lt;/os_type&gt;
    &lt;arch name="x86_64"&gt;
      &lt;wordsize&gt;64&lt;/wordsize&gt;
      &lt;domain type="xen"&gt;&lt;/domain&gt;
      &lt;emulator&gt;/usr/lib64/xen/bin/qemu-dm&lt;/emulator&gt;
    &lt;/arch&gt;
    &lt;features&gt;
    &lt;/features&gt;
  &lt;/guest&gt;</span>

  &lt;!-- hvm-3.0-x86_32 --&gt;
  <span style="color: #00B200">&lt;guest&gt;
    &lt;os_type&gt;hvm&lt;/os_type&gt;
    &lt;arch name="i686"&gt;
      &lt;wordsize&gt;32&lt;/wordsize&gt;
      &lt;domain type="xen"&gt;&lt;/domain&gt;
      &lt;emulator&gt;/usr/lib/xen/bin/qemu-dm&lt;/emulator&gt;
      &lt;machine&gt;pc&lt;/machine&gt;
      &lt;machine&gt;isapc&lt;/machine&gt;
      &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
    &lt;/arch&gt;
    &lt;features&gt;
      &lt;cpuselection/&gt;
      &lt;deviceboot/&gt;
    &lt;/features&gt;
  &lt;/guest&gt;</span>
  ...
&lt;/capabilities&gt;</pre>
        <p>The first block (in red) indicates the host hardware
          capabilities, such as CPU properties and the power
          management features of the host platform.  CPU models are
          shown as additional features relative to the closest base
          model, within a feature block (the block is similar to what
          you will find in a Xen fully virtualized domain
          description). Further, the power management features
          supported by the host are shown, such as Suspend-to-RAM (S3),
          Suspend-to-Disk (S4) and Hybrid-Suspend (a combination of S3
          and S4). In case the query for power
          management features succeeded but the host does not support
          any such feature, then an empty &lt;power_management/&gt;
          tag will be shown. Otherwise, if the query itself failed, no
          such tag will be displayed (i.e., there will not be any
          power_management block or empty tag in the XML).</p>
        <p>The second block (in blue) indicates the paravirtualization
          support of the Xen support, you will see the os_type of xen
          to indicate a paravirtual kernel, then architecture
          information and potential features.</p>
        <p>The third block (in green) gives similar information but
          when running a 32 bit OS fully virtualized with Xen using
          the hvm support.</p>
        <p>This section is likely to be updated and augmented in the
          future,
          see <a href="https://www.redhat.com/archives/libvir-list/2007-March/msg00215.html">the
          discussion</a> which led to the capabilities format in the
          mailing-list archives.</p>

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