Re: [RFC patch 0/2] posix mqueue namespace (v11)

[Cedric Le Goater <clg-NmTC/0ZBporQT0dZR+AlfA@public.gmane.org>]

Serge E. Hallyn wrote:
> (Ok I don't know what the actual version number is - it's
> high but 11 is probably safe)
> 
> Cedric and Nadia took several approaches to making posix
> message queues per-namespace.  I ended up mamking some
> deep changes so am not retaining their Signed-off-by:s
> on this version, but this is definately very much based
> on work by both of them.

you can keep mine. i have had a similar version on 2.6.26. 

http://legoater.free.fr/patches/2.6.26/2.6.26/

and it's easier to track where the patches go.

> Patch 2 hopefully explains my approach.  Briefly,
> 
> 	1. sysv and posix ipc are both under CLONE_NEWIPC
> 	2. the mqueue sb is per-ipc-namespace
> 
> So to create a new ipc namespace, you would
> 
> 	unshare(CLONE_NEWIPC|CLONE_NEWNS);

does CLONE_NEWIPC requires CLONE_NEWNS ? 

> 	umount /dev/mqueue
> 	mount -t mqueue mqueue /dev/mqueue

the semantic looks good, much better than a 'newinstance' mount 
option.

if CLONE_NEWNS is not required, what happens to the user mount (and
the mq_ns below it) when the task dies. that's the big issue. if 
CLONE_NEWNS is required were safe, but I think Pavel made
some objection to that. 

> It's perfectly valid to do vfs operations on files
> in another ipc_namespace's /dev/mqueue, but any use
> of mq_open(3) and friends will act in your own ipc_ns.

ok.

C.