<domain>

  <devices>

    <filesystem type="file" accessmode="mapped">

      <driver type="nbd" format="qcow2"/>

      <source file="/path/to/source"/>

      <target dir="/path/to/target1"/>

      <readonly/>

    </filesystem>

    <filesystem type="ram" accessmode="passthrough">

      <driver type="path"/>

      <source usage="1234" units="bytes"/>

      <target dir="/path/to/target2"/>

    </filesystem>

  </devices>

</domain>