It's a BlockBackend wrapper of the BDS interface.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20180601092648.24614-10-famz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>