netdev - Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

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Date:	Wed, 3 Mar 2010 09:38:00 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Ben Greear <greearb@...delatech.com>
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

Quoting Eric W. Biederman (ebiederm@...ssion.com):
> Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com> writes:
> 
> > Eric W. Biederman [ebiederm@...ssion.com] wrote:
> > | 
> > | I think replacing a struct pid for another struct pid allocated in
> > | descendant pid_namespace (but has all of the same struct upid values
> > | as the first struct pid) is a disastrous idea.  It destroys the
> >
> > True. Sorry, I did not mean we would need a new 'struct pid' for an
> > existing process. I think we talked earlier of finding a way of attaching
> > additional pid numbers to the same struct pid.
> 
> I just played with this and if you make the semantics of unshare(CLONE_NEWPID)
> to be that you become the idle task aka pid 0, and not the init task pid 1 the
> implementation is trivial.

Heh, and then (browsing through your copy_process() patch hunks) the next
forked task becomes the child reaper for the new pidns?  <shrug>  why not
I guess.

Now if that child reaper then gets killed, will the idle task get killed too?
And if not, then idle task can just re-populating the new pidns with new
idle tasks...

If this brought us a step closer to entering an existing pidns that would
be one thing, but is there actually any advantage to being able to
unshare a new pidns?  Oh, I guess there is - PAM can then use it at
login, which might be neat.

-serge
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