[libvirt] Re: RFC: API additions for enhanced snapshot support

or, to merge all of base.img into snapshot.qcow2 then change snapshot.qcow2 to no longer have a backing file, before deleting base.img. As I understand it, either file can be deleted when a snapshot is no longer needed, but having the flexibility to decide which of the two files to delete would be useful, and may require knowing how dirty the snapshot file is in relation to the original file (if it is 95% dirty, it is faster to just pull in the last few blocks from base into snapshot before deleting base, whereas if it is only 5% dirty, it is faster to sync the dirtied blocks from snapshot back to base before deleting snapshot). And even if you have control over which of the two images to delete, you may also want to have control over the final filename used for the merged image (that is, in the 5% dirty case, use the snapshot->base merge followed by rename(base,snapshot), rather than wasting time on the base->snapshot merge, to still get the end result that the final filename is snapshot).