[Devel] Re: [PATCH v7 09/10] IPC: message queue copy feature introduced

[Stanislav Kinsbursky]

18.10.2012 15:52, Eric W. Biederman пишет:
> Stanislav Kinsbursky <skinsbursky at parallels.com> writes:
>
>> First of all, this problem exist as is regardless to C/R feature or this patch
>> set. If you share some resource (like message queue in this particular case)
>> system-wide, then any process A can read out a message, which was send by
>> process B to process C. So, when processes uses IPC message queues, they should
>> be designed to handle such failures.
>>
>> Second, it's up to user-space how to handle such things. It's implied, that
>> user, trying to migrate some process, holding one end of queue, will also
>> migrate another process, holding second end.
>>
>> Third, there is IPC namespace, which isolates IPC objects. It can be used for
>> safe migration of process tree.
>
> This does raise an interesting question.
>
> What is the point of the message copy feature?  It appears to be simply
> an optimization and not needed to actually perform the
> checkpoint/restart.  If you are going to restart the processes you can
> read all of the messages and then write all of the messages back before
> you restart the processes.
>

It's not just an optimisation.
If crtools will fail (with SIGSEGV, for instance), then queue will be empty.

> Eric
>


-- 
Best regards,
Stanislav Kinsbursky