[PATCH cgroup/for-3.11] cgroup: disallow rename(2) if sane_behavior

[Tejun Heo]

On Mon, Jun 17, 2013 at 06:33:53PM +0200, Lennart Poettering wrote:
> On Sun, 16.06.13 15:15, Tejun Heo (tj at kernel.org) wrote:
> 
> > We want composability regardless of migration, but as for migration
> > itself, an alternative could be having an atomic "move everything in
> > cgroup A to cgroup B" interface, so that the admin (whether human or
> > base system software) can set up a new cgroup and then move the member
> > tasks atomically.
> 
> I am not sure this would cut it for containers. For containers we'll
> usually have a fully populated cgroup subtree, and if we want to migrate
> that somewhere else, then we'd something that works recursively and
> allows us to not tell the container at all about the move (i.e. the
> namespace of cgroupfs the container sees should ideall stay entirely
> unaltered by the move).

Right, I somehow completely forgot about the sub-hierarchy.  We can
require the userland to set up the same sub-hierarchy with new configs
and do migration recursively but that's just yucky and there's no way
to make such operations invisible to the users of the sub-hierarchy.
If we're gonna do it, I agree the only sane way is properly
implementing migration via rename(2).

Thanks.

-- 
tejun