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

[Eduardo Habkost]

Excerpts from Anthony Liguori's message of Mon Nov 23 14:44:04 -0200 2009:
> 
> I don't want to transparently migrate from 5.4.1 to 5.4.0 and have my 
> guest's time start drifting.  I specifically want that to fail.

If you migrate from 5.4.0 to 5.4.0 or from 5.4.0 to 5.4.1, the guest
will also start drifting. Do you expect migration to fail on all those
cases too?


>
<snip>
> You've made a policy decision.  As a user, I really don't like that 
> policy decision and it makes me want to make sure that we upgrade all of 
> our hosts at once to avoid this problem.  Of course, I'm a control freak 
> and I'm particularly concerned about time drift issues as that's been 
> consuming a bit of my time lately.
<snip>
> 
> Can we reasonably support a guest that doesn't have this older field?  
> If the answer is "yes", then it's a feature that can be delayed until 
> the next release.

If you are really concerned about the time drift as you say above, the
answer is "no". A guest that doesn't have the new fields on savevm will
start drifting as soon as it is migrated--it doesn't matter if it is a
forward, backward, or sideways migration.
-- 
Eduardo