Re: [Qemu-devel] Re: [PATCH v3 0/5] Add QMP migration events

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 11 Jun 2010 09:38:42 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> >   1. QMP only returns the response when the command is finished, eg:
> >
> >      C: { "execute": "migrate", "id": "foo" ... }
> >      /* nothing is returned, other commands are issued, after several hours... */
> >      S: { "return": ... "id": "foo" }
> >    
> 
> This is how just about every RPC mechanism works...

 Let's go for it then.

> >> - MIGRATION_STARTED:  somebody started a migration, it is emited on
> >>    source and target, all monitors receive this event.
> >>      
> >   The client has started the migration, it knows it. Why is the event needed?
> >    
> 
> I think we've more or less agreed that MIGRATION_CONNECTED is really the 
> event we want.

 Is it useful in the source or in the target?

> >> - MIGRATION_ENDED: migration ended with sucess, all needed data is in
> >>    target machine.  Also emitted in all monitors on source and target.
> >>
> >> - MIGRATION_CANCELED: in one of the source monitors somebody typed:
> >>    migrate_cancel.  It is only emmited on the source monitors, target
> >>    monitors will receive a MIGRATION_FAILED event.
> >>
> >> - MIGRATION_FAILED (with this error).  At this point we don't have
> >>    neither the QMP infraestructure for sending (with this error) nor
> >>    migration infrastructure to put there anything different than -1.
> >>      
> >   Aren't all the three events above duplicating the async response?
> >    
> 
> Yes.  Today, we should just generate a MIGRATION_DONE event and let a 
> client poll for failure status.

[...]

> MIGRATION_DONE gets deprecated for 0.14.

 Yeah, this removes the need for polling in 0.13, but I was wondering if
it's worth it. If I'm not mistaken, libvirt does the polling when working
with the text Monitor and I believe it's not a big deal to keep it until 0.14.