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

[Eric W. Biederman]

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.

Eric