Re: [Qemu-devel] [PATCH 4/6] snapshot: implemention of common API to take snapshots

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Dec 21, 2012 at 06:20:40AM +0000, Dietmar Maurer wrote:
> >    If libvirt could integrate external tool using code, that would be great. For
> > qemu, My understanding is just to take internal snapshot and stop vm,
> 
> You just need to save VM state, flush all IO requests, then stop.
> 
> After that the management framework can issue command to:
> 
> * create internal snapshots (qmp)
> * create external snapshots (qmp)
> * create snapshot using external tools (lvcreate, nexenta API, btrfs?, ...)
> 
> > then let management stack do the things remain. Dietmar, do you think that is all
> > what needed in qemu?
> 
> Basically yes. Maybe we need to provide some 'abort/cleanup' handler to restore
> state if something fail (AFAIK external snapshots needs that).

Yes, I agree that we several steps that can be orchestrated over QMP -
and remember the QEMU guest agent which can ensure consistent backups.

External snapshots (LVM, btrfs, etc) should happen outside of QEMU,
usually in the management stack.  It's not just beyond the scope of QEMU
to execute LVM, btrfs, etc tools but also not possible when SELinux or
file descriptor passing are used.

Stefan