Re: [Qemu-devel] [PATCH 5/7] block: allow migration to work with image files (v2)

[Anthony Liguori <aliguori@us.ibm.com>]

On 11/14/2011 07:11 AM, Juan Quintela wrote:
>
>> diff --git a/cpus.c b/cpus.c
>> index 82530c4..ae5ec99 100644
>> --- a/cpus.c
>> +++ b/cpus.c
>> @@ -398,6 +398,7 @@ static void do_vm_stop(RunState state)
>>           vm_state_notify(0, state);
>>           qemu_aio_flush();
>>           bdrv_flush_all();
>> +        bdrv_invalidate_cache_all();
>>           monitor_protocol_event(QEVENT_STOP, NULL);
>>       }
>
> This is too much. Reopening all qcow2 images each time that we stop the
> vm looks excesive, no?

This general code came in via:

http://mid.gmane.org/cover.1290613959.git.mst@redhat.com

That series made migration stable after issuing a stop operation.  I believe the 
justification was for debugging purposes or something like that.

At any rate, invalidating the cache is part of what's required to make things 
stable.  If you look at something like cache=unsafe, the only way the metadata 
will get flushed if via a bdrv_close since bdrv_flush is a nop.

So this is needed as long as we care about supporting this use-case.

Regards,

Anthony Liguori

>
> Later, Juan.
>