[PATCH] [RFC] c/r: Add UTS support

[Serge E. Hallyn]

Quoting Daniel Lezcano (daniel.lezcano at free.fr):
> Dan Smith wrote:
> > DL> I guess it will be esay to implement with a nsproxy level counter.
> > DL> Each time you unshare, the new nsproxy count is incremented.
> > DL> Assuming the init_nsproxy is level 0, when the nsproxy counter is
> > DL> > 1, the process is uncheckpointable.
> >
> > This should also be possible by just making sure that the nsproxy of
> > the root process being checkpointed is the same as any of the
> > children, correct?  That way we avoid having to modify the core
> > nsproxy bits and can still reject any nested namespaces.
> >   
> Right, this is another option. The nsproxy counter will allow to flag at 
> runtime a process to be uncheckpointable. The nsproxy comparison will 
> detect nested nsproxies at checkpoint time.

Or, to stick more to the resource->may_checkpoint way of doing it, you
setbit(&nsproxy->uts_ns->may_checkpoint, 0) when the uts_ns is
created, and anytime a task does clone(CLONE_NEWUTS) or
unshare(CLONE_NEWUTS), you clear the bit on the parent uts_ns.

-serge