Re: [libvirt] [RFC]: Snapshot API

On Wed, Mar 24, 2010 at 09:09:08AM -0400, Chris Lalancette wrote: > On 03/24/2010 04:52 AM, Paolo Bonzini wrote: > > > > >> > How can<parent>  be settable? If I have snapshots A and B > >> > > >> >    A ->  B ->  current state > >> > > >> > and I create a new snapshot C, then B will be the parent of C. > >> > > >> >    A ->  B ->  C ->  current state > >> > > >> > If I create another snapshot D now and specify A to be its parent, > >> > what's supposed to happen then? > >> > >> You are right, that doesn't make that much sense.  I have to admit that > >> the tree structure is the part I thought about least, so I'll take that > >> part back. <parent> is just going to be an informational field about > >> which snapshot was current (if any) when this one was created. > > > > If discarding a snapshot also discards the children, it would definitely > > make sense to be able to specify the parent. > > The problem, though, is what Mattias points out; there is no (easy) way > that, given state C, I can get back to state A to make a new snapshot. > I actually have to be at state A to take a new snapshot with a parent of > A.  I think this is a place where we have to make it manual; if you really > want a new snapshot that is a child of A, you'll have to manually shutdown > your domain, boot to snapshot A, then take a snapshot of A. This is something virDomainCreateAtSnapshot() should solve. If you have a series   A -> B -> C And you do  virDomainCreateAtSnapshot(dom, "A"), then you get 'D'   A -> B -> C   |   \-> D

B & C are still valid IIUC, this is how VMWare works & we essentially need our API to map to that since VirtualBox seems to follow the VMWare model too & there's no reason that QEMU can't too.