Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts

[Gerd Hoffmann]

  Hi,

> > Doesn't work.  If you have a qemu 0.11 machine, a virtio nic and your
> > guest uses MSI-X you simply can't migrate to qemu 0.10.  End of story.
> > If you want to be able to migrate to 0.10 you have to start in 0.10
> > compat mode with MSI-X disabled.  So IMHO it does makes sense to tie the
> > savevm format to -M pc-<version>.
> >
> > cheers,
> >    Gerd
>
> MSI-X is an orthogonal issue, let's not mix it in.

It isn't.  I was making that point with feature=MSI-X.  The same 
argument is true for any other feature:  If $feature is new in qemu 
$newversion and you are using it you can't migrate to qemu $oldversion 
which hasn't $feature.  The versioned machine types turn $feature in 
$newversion, so migration to $oldversion could work.

cheers,
  Gerd