Flatten volume from glance rbd image for cinder rbd backend for Cinder

Suppose glance and cinder uses ceph rbd driver as storage backend, cinder and glance are in the same ceph storage cluster. If cinder creates a volume from an image, it could create a clone volume from that image, and the relationship is 'glance image-->rbd snap of glance image-->clone image(=volume from image)'' li...