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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;/cpu&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;/features&gt;
  &lt;/guest&gt;</span>
  ...
&lt;/capabilities&gt;</pre>
        <p>The first block (in red) indicates the host hardware capabilities, currently
it is limited to the CPU properties but other information may be available,
it shows the CPU architecture, and the features of the chip (the feature
block is similar to what you will find in a Xen fully virtualized domain
description).</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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