<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>