Re: [Qemu-devel] [PATCH 2/3] move vm stop/start to migrate_set_state

[Dor Laor <dlaor@redhat.com>]

On 07/13/2009 05:52 PM, Anthony Liguori wrote:
> Gleb Natapov wrote:
>> With unreliable socket it doesn't matter what write() returns data may
>> or may not reach the destination regardless, with reliable sockets
>> write() succeeds only after data was acked by the receiver, but it still
>> doesn't mean that data will be read from destination socket.
>
> You are correct and we handle both of these cases appropriately. In the
> event that we think we completed a migration successfully and we really
> didn't because of a lost network connection, the result is both the
> source and destination are stopped. A third party can resume the source
> and continue along happily.
>
> The case being debated is whether write() can ever actually complete and
> yet still return an error. In this case, since we automatically resume
> the source on error, the result would be two copies of the VM running.
>
> I haven't seen any evidence that this case could actually happen other
> than theoretic speculation. I just at the migration code and it's not a
> simple change to try and be conservative wrt this case because of the
> way we do buffering.
>

Reminder: please remember to commit for saving the running state so we 
won't resume paused guest after successful migration.


> Regards,
>
> Anthony Liguori
>
>> --
>> Gleb.
>
>
>