[Patch 0/3] posix mqueue namespace (v14)

[Serge E. Hallyn]

IPC namespaces are completely disjoint id->object mappings.
A task can pass CLONE_NEWIPC to unshare and clone to get
a new, empty, IPC namespace.  Until now this has supported
SYSV IPC.

Most Posix IPC is done in userspace.  The posix mqueue
support, however, is implemented on top of the mqueue fs.

This patchset implements multiple mqueue fs instances,
one per IPC namespace to be precise.

To create a new ipc namespace with posix mq support, you
should now:

	unshare(CLONE_NEWIPC|CLONE_NEWNS);
	umount /dev/mqueue
	mount -t mqueue mqueue /dev/mqueue

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.
After the ipc namespace has exited, you can still
unlink but no longer create files in that fs (since
accounting is carried.

Changelog:
	v14: (Jan 16 2009) port to linux-next
	v13: (Dec 28 2009)
	   1. addressed comments by Dave and Suka
	   2. ported Cedric's patch to make posix mq sysctls
	      per-namespace

When convenient, it would be great to see this tested
in -mm.

thanks,
-serge