Re: [PATCH v3 2/5] migration: Create MigrationState active field

[Juan Quintela]

"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> Right now, there is no easy way to dectect if we have already
>> cancelled/finished/failed a migration.  This field is setup to true
>> when we start a migration, and it is set to false as soon as we stop
>> it.
>> 
>> It fixes a real bug, in ram_save_iterate() we call functions that
>> wrote to the channel even if we know that migration has stopped for
>> any reason.  This gives problems with multifd because we need to
>> synchronize various semoaphores that we don't want to take.
>> 
>> Signed-off-by: Juan Quintela <address@hidden>
>
> Why can't you use migration_is_active() in the ram.c case?
> My preference would be just to stick with something derived
> from the state rather than tacking another state bit on.

Trying to redo this as something more reasonable.
Problem that I was trying to do is being sure that we know in what state
we are.  Real migration states are:

- NOT_STARTED: We haven't even started
- SETUP: We have started with local stuff but haven't yet transmitted
  anything
- ACTIVE: Migration is donig well, we are trasnmitting data
- FINISHED: We have finished migration (COMPLETED/FAILED/CANCELLED/CANCELLING)
- COLO: Yet a completelly different can of worms

To make things even more interesting, we export ->state, so code can do
whatever they want with that variable.

What do we need in a lot of places:
- migration_is_running() (i.e. channel is still open).

And we go left and right to be sure what is going on.

>> @@ -2834,6 +2836,7 @@ static void migration_completion(MigrationState *s)
>>      }
>>  
>>      if (!migrate_colo_enabled()) {
>> +        s->active = false;
>>          migrate_set_state(&s->state, current_active_state,
>>                            MIGRATION_STATUS_COMPLETED);
>
> You've not always got these two the same way around - i.e. do you change
> the state first or do you set the active state first?  I think it needs
> to be consistent.

As said, I will try to move that to inside migrate_set_state()

thanks, Juan.