[Qemu-devel] Re: [PATCH 3/5] QMP: Introduce MIGRATION events

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, May 25, 2010 at 06:43:13PM +0200, Juan Quintela wrote:
> Anthony Liguori <anthony@codemonkey.ws> wrote:
> > On 05/25/2010 11:25 AM, Daniel P. Berrange wrote:
> >> On Tue, May 25, 2010 at 06:04:17PM +0200, Juan Quintela wrote:
> >>    
> >>> Anthony Liguori<anthony@codemonkey.ws>  wrote:
> 
> > I'm not sure why you would need a notification of when migration
> > starts (since you know when you've started migration).
> 
> But you don't know if the other end "knows" that it has also started.
> 
> started is needed only in incoming part, because .... we don't have a
> monitor to ask if migration has started.

If we ever want to get closer to allowing multiple monitors, or allowing
apps to issue QMP commands directly via libvirt, then we still need the
'migration started' event on the source, because something else can 
have issued the 'migrate' command without the mgmt app knowing.

MIGRATED_STARTED+STOPPED really *is* needed if we're to make QMP cope 
with all possible use cases. If we rely on inferring it from STOP+RESUME
events, it is going to exclude a significant set of use cases, and likely
result in this being proposed all over again in 12 months time :-(

Regards,
Daniel
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