Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions

[Paul Brook <paul@codesourcery.com>]

On Wednesday 10 June 2009, Michael S. Tsirkin wrote:
> On Wed, Jun 10, 2009 at 05:46:03PM +0100, Paul Brook wrote:
> > > > If you can't create an identical machine from scratch then I don't
> > > > consider snapshot/migration to be a useful feature. i.e. as soon as
> > > > you shutdown and restart the guest it is liable to break anyway.
> > >
> > > Why is liable to break?
> >
> > A VM booted on an old version of qemu and migrated to a new version will
> > behave differently to a the same VM booted on a new version of qemu.
>
> It will behave identically. That's what the patch does: discover
> how did the device behave on old qemu, and make it behave the same way
> on new qemu.

You're missing the point.  After doing a live migration from old-qemu to new-
qemu, there is no snapshot to load.  We need to be able to shutdown the guest, 
kill qemu (without saving a snapshot), then start qemu with the exact same 
hardware.

If we can't start a new qemu with the same hardware configuration then we 
should not be allowing migration or loading of snapshots.

Paul