Re: [patch] PID namespace design bug, workaround

[Arjan van de Ven <arjan@infradead.org>]

On Sat, 3 Nov 2007 15:40:48 -0700 (PDT)
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> I don't understand how you can call this a "PID namespace design
> bug", when it clearly has nothing what-so-ever to do with pid
> namespaces, and everything to do with the *futexes* that blithely
> assume that pid's are unique and that made it part of the
> user-visible interface.
> 
> OF COURSE any pid namespace design will always break such
> assumptions, but that's not because of any PID namespace bugs. It's
> what the whole *point* of PID namespaces are. If you use pid's
> (instead of some opaque cookies), you will not be able to use such
> things across pid-separation.

well... kind of.
THere are 2 things around pid namespaces: which pids you can see/touch
(in proc or signals or otherwise), and the non-uniqueness.

For containers you clearly want the first part... but... is there a
strong reason to not just *not* create duplicate pids even across
namespaces? there's no rule in posix or anything similar to fd's afaik
concerning which pids we can hand out... so we could just make then
unique globally but just with limited visibility....