[libvirt] Storage Backend - buildVolFrom Semantics

[Richard Laager]

storage_backend_rbd.c uses an RBD clone operation to implement buildVolFrom.

If I'm understanding the RBD documentation correctly, you cannot delete 
the parent until the clone has been deleted:
http://docs.ceph.com/docs/master/dev/rbd-layering/
"Before cloning a snapshot, you must mark it as protected, to prevent it 
from being deleted while child images refer to it:"
&
"To delete the parent, you must first mark it unprotected, which checks 
that there are no children left:"

Is libvirt okay with those semantics for volumes? That is, if you clone 
a volume, is it acceptable that you cannot delete the parent until you 
delete the clone?

The answer to this affects how I'll write a patch to implement 
buildVolFrom for storage_backend_zfs.c.

-- 
Richard