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

[Michael S. Tsirkin]

On Thu, Dec 03, 2020 at 12:16:24PM +0000, Daniel P. Berrangé wrote:
> On Thu, Dec 03, 2020 at 07:11:17AM -0500, Michael S. Tsirkin wrote:
> > On Thu, Dec 03, 2020 at 11:43:41AM +0000, Dr. David Alan Gilbert wrote:
> > > Another way to solve this would be to remove the unplugging from the
> > > migration layer and leave it as a problem for the management layer to do
> > > the unplug.
> > 
> > Daniel described the problem with modular management tools which expect
> > pausing or slowing down guest to cause migration to converge.
> > 
> > Point is, it actually *will* make it converge but only if you
> > pause it after unplug.
> > 
> > As it is, these tools fundamentally can not handle failover
> > requiring guest cooperation. Moving code between layers won't help.
> > Introducing failure modes as this patch does won't help either
> > especially since Daniel wrote there are countless tools like this.
> > We just break them all but have no resources to fix them,
> > this does not help at all.
> > 
> > We can just leave the situation as is.
> > 
> > Or if we do want to be nice to these tools, how about we
> > unpause the guest until unplug, then pause it again?
> > This actually addresses the problem instead of
> > shifting the blame, does it not?
> 
> This is a very bad idea because it changes the execution status of the
> guest behind the apps/admins back, and that cannot be assumed to be a
> safe thing todo.
> 
> Regards,
> Daniel

My question is this: management gets an error since guest was paused
presumably by someone (admin?) outside its control.
How does it know when it is unpaused?


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