linux-kernel - Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:)

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Message-ID: <20110616130613.GC19312@redhat.com>
Date:	Thu, 16 Jun 2011 15:06:13 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cedric Le Goater <clg@...ibm.com>
Cc:	Greg Kurz <gkurz@...ibm.com>, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, containers@...ts.osdl.org,
	akpm@...ux-foundation.org, xemul@...nvz.org
Subject: Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was
	Vpid:)

On 06/16, Cedric Le Goater wrote:
>
> We have a case where a task in a parent pid namespace needs to kill
> another task in a sub pid namespace only knowing its internal pid.
> the latter has been communicated to the parent task through a file or
> a unix socket.

OK, thanks, this partly answers my question... But if they communicate
anyway, it is not clear why the signal is needed.

> This 'ActivePid' information in /proc is not sufficient to identity
> the task, you also need the list of the tasks which are living in
> the pid namespace.

Yes, I see.

> a new kill syscall could be the solution:
>
>     int pidns_kill(pid_t init_pid, pid_t some_pid);
>
> where 'init_pid' identifies the namespace and 'some_pid' identifies
> a task in this namespace. this is very specific but why not.

Yes, I also thought about this. Should be trivial.

Or int sys_tell_me_its_pid(pid_t init_pid, pid_t some_pid).




Just in case.... This is hack, yes, but in fact you do not need the
kernel changes to send a signal inside the namespace. You could
ptrace sub_init, and execute the necessary code "inside" the namespace.

Oleg.

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