<volume type='file'>

<name>volume_name.qcow2</name>
<source>
</source>
<capacity unit='GiB'>capacity</capacity>
<allocation unit='GiB'>0</allocation>
<target>
  <path>/path/to/volume_name.qcow2</path>
  <format type='qcow2'/>
</target>

</volume>