(
  source only properties:
  {
    "driver": "file",
    "filename": "/var/lib/libvirt/images/a"
  }
  backing store string:
  /var/lib/libvirt/images/a
)
(
  source only properties:
  {
    "driver": "file",
    "filename": "/var/lib/libvirt/images/b"
  }
  backing store string:
  /var/lib/libvirt/images/b
)
(
  source only properties:
  {
    "driver": "gluster",
    "volume": "images",
    "path": "c",
    "server": [
      {
        "type": "inet",
        "host": "test.org",
        "port": "24007"
      }
    ]
  }
  backing store string:
  gluster://test.org:24007/images/c
)
(
  source only properties:
  {
    "driver": "file",
    "filename": "/var/lib/libvirt/images/d"
  }
  backing store string:
  /var/lib/libvirt/images/d
)