Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest

[Daniel P . Berrangé]

On Wed, Dec 02, 2020 at 05:31:50AM -0500, Michael S. Tsirkin wrote:
> On Wed, Dec 02, 2020 at 10:27:18AM +0000, Daniel P. Berrangé wrote:
> > On Wed, Dec 02, 2020 at 05:13:18AM -0500, Michael S. Tsirkin wrote:
> > > On Wed, Nov 18, 2020 at 09:37:22AM +0100, Juan Quintela wrote:
> > > > If we have a paused guest, it can't unplug the network VF device, so
> > > > we wait there forever.  Just change the code to give one error on that
> > > > case.
> > > > 
> > > > Signed-off-by: Juan Quintela <quintela@redhat.com>
> > > 
> > > It's certainly possible but it's management that created
> > > this situation after all - why do we bother to enforce
> > > a policy? It is possible that management will unpause immediately
> > > afterwards and everything will proceed smoothly.
> > > 
> > > Yes migration will not happen until guest is
> > > unpaused but the same it true of e.g. a guest that is stuck
> > > because of a bug.
> > 
> > That's pretty different behaviour from how migration normally handles
> > a paused guest, which is that it is guaranteed to complete the migration
> > in as short a time as network bandwidth allows.
> > 
> > Just ignoring the situation I think will lead to surprise apps / admins,
> > because the person/entity invoking the migration is not likely to have
> > checked wether this particular guest uses net failover or not before
> > invoking - they'll just be expecting a paused migration to run fast and
> > be guaranteed to complete.
>
> Okay I guess. But then shouldn't we handle the reverse situation too:
> pausing guest after migration started but before device was
> unplugged?

Yeah we likely want todo something there.

Regards,
Daniel
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