[Sheepdog] [PATCH 1/2] sheep: sheep: handle node change event first

[MORITA Kazutaka]

At Sun, 01 Apr 2012 14:06:54 +0800,
Liu Yuan wrote:
> 
> On 04/01/2012 01:59 PM, MORITA Kazutaka wrote:
> 
> > 'join C' is processed after there is no outstanding I/Os.
> > 
> 
> 
> Okay, I see the race.
> 
> can we remove this line in start_cpg_event_work()
> 
>         if (is_membership_change_event(cevent->ctype) &&
> sys->nr_outstanding_io)
>                 return;

No, Sheepdog assumes that the older epoch directories are read-only
(especially in recovery codes), so we need to flush all I/Os before
updating an epoch.  I think it is much harder to remove this line than
introducing two queues.

Thanks,

Kazutaka