def direct_snapshot(self, context, snapshot_name, image_format, image_id,
                        base_image_id):
        """Prepare a snapshot for direct reference from glance

        :raises: exception.ImageUnacceptable if it cannot be
                 referenced directly in the specified image format
        :returns: URL to be given to glance
        """
        raise NotImplementedError(_('direct_snapshot() is not implemented'))