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

[Paul Brook]

On Wednesday 10 June 2009, Michael S. Tsirkin wrote:
> On Wed, Jun 10, 2009 at 04:15:04PM +0100, Paul Brook wrote:
> > > > That's seems just plain wrong to me.
> > > > Loading a VM shouldn't not
> > > > do anything that can't happen during normal operation.
> > >
> > > At least wrt pci, we are very far from this state: load just overwrites
> > > all registers, readonly or not, which can never happen during normal
> > > operation.
> >
> > IMO that code is wrong. We should only be loading things that the guest
> > can change (directly or indirectly).
>
> Making it work this way will mean that minor changes to a device can
> break backwards compatibility with old images, often in surprising ways.
> What are the advantages?

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.

It may be that the snapshot/migration code wants to include a machine config, 
and create a new machine from that. However this is a separate issue, and 
arguably something your VM manager should be handling for you.

Paul