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

[Liu Yuan]

On 04/01/2012 02:21 PM, MORITA Kazutaka wrote:

> 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.
> 


How about flushing the IO before inserting the Join/Leave Event at the
head?  That is, before inserting, we check
	if sys->nr_outstanding_io == 0

This can be thought as move this line in front of inserting.

Thanks,
Yuan