On Wed, Nov 25, 2009 at 03:10:16PM +0100, Gerd Hoffmann wrote: > 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
We were discussing features that are (mostly) not user-visible. It is clear that if you have a user-visible change you have a different machine, so you can not migrate. Now if you fix a bug by changing savevm format, without user visible changes you *also* can not migrate, but this does not make it into feature or make it a good fit for machine description. -- MST
