Paolo Bonzini wrote:
On 11/23/2009 02:51 PM, Eduardo Habkost wrote:
Right, but I wouldn't be surprised if a user complains that "I know that
my guest don't use that VM feature, so I want to be able to migrate to
an older version anyway".
That's a bit more tricky. What if the older version doesn't support
sound (just making up an example) and you know that you're not using a
client that plays sound, but still the sound card is part of the
machine? I think there is no doubt that the migration (or
save/restore) should be aborted in that case.
I would not generalize very much, the problem that Dor posed is very
specific and probably quite rare. However, it's real.
I think the problem is that you shouldn't be changing the guest visible
state in a stable update of qemu. If you change the guest visible state
in a stable update, then you won't be able to support live migration
between arbitrary stable versions. You can't introduce features without
introducing forward compatibility issues. If you're adding new guest
visible state, you've added a feature.
This is not a live migration problem, this is a problem with your stable
branch policy.
Regards,
Anthony Liguori
Paolo