'Returns the pool, image and snapshot name for the parent of an
RBD volume.
:volume: Name of RBD object
:pool: Name of pool'

def parent_info(self, volume, pool=None):

    try:
        with RBDVolumeProxy(self, str(volume), pool=pool, read_only=True) as vol:
            return vol.parent_info()
    except rbd.ImageNotFound:
        raise exception.ImageUnacceptable((_('no    usable    parent    snapshot    for    volume    %s') % volume))
