<disk type='file' device='disk'>
  <driver name='qemu' type='raw' cache='none'/>
  <source file='/dev/null'/>
  <target dev='hda' bus='virtio'/>
  <readonly/>
  <shareable/>
  <address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0001'/>
</disk>