Processes with multiple pid_t values

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm at xmission.com):
> Sukadev Bhattiprolu <sukadev at us.ibm.com> writes:
> 
> > A process that unshares its namespace gets a new pid_t in the child
> > namespace. Simlarly its process group and session leaders get new pid_ts
> > in the child namespace right ?
> >
> > i.e do the following pid_ts look reasonable when process 1234 unshares
> > its pid namespace ?
> >
> >
> > 		PID	PPID	PGID	SID
> >
> > init pid ns	1234	1233	1230	1220
> >
> > child pid ns	3	2	1	0	
> 
> A slightly more complete answer.
> 
> A pid that cannot be represented in the current pid namespace should be
> 0.
> 
> pid 1 is very special and in the case of a clone should definitely
> be the first pid in the namespace.
> 
> In the case of an unshare pid == 1 is probably the process that does
> the unshare, and it's children all show up in the child namespace.

Sigh, here we go back again to the question of what to do in the case
of a lightweight container which doesn't have a /sbin/init.  Let's say
I do
	spawn_container(fork_and_exit(sleep 30m));

so pid 1 forks, pid 2 sleeps 30 minutes, but pid 1 exits right after
the fork.  What do we do?  Create an idle pid 1?  Tack a struct pid
to the parent namespaces' pid=1 making it pid=1 for the child namespace?

-serge