| Re: [PATCH v7 09/10] IPC: message queue copy feature introduced [message #48496 is a reply to message #48494] |
Thu, 18 October 2012 14:40   |
Stanislav Kinsbursky
Messages: 683
Registered: October 2011
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Senior Member |
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18.10.2012 15:52, Eric W. Biederman пишет:
> Stanislav Kinsbursky <skinsbursky@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
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