2010/3/24 Daniel P. Berrange <berrange@redhat.com>:
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
You mean you get D when you do a virDomainSnapshotCreateXML(dom, NULL) _after_ you've done a virDomainCreateAtSnapshot(dom, "A"), don't you?
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.
Yes, that's how I understand the VMware and VirtualBox snapshot model. I'll do some testing to be really sure. Matthias