Date: Thu, 16 Jun 2011 15:06:13 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Cedric Le Goater <clg@fr.ibm.com>
Cc: Greg Kurz <gkurz@fr.ibm.com>, linux-kernel@vger.kernel.org,
        ebiederm@xmission.com, containers@lists.osdl.org,
        akpm@linux-foundation.org, xemul@openvz.org
Subject: Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was
	Vpid:)
Message-ID: <20110616130613.GC19312@redhat.com>
References: <20110615145527.4016.70157.stgit@bahia.local> <20110615190302.GA16440@redhat.com> <1308223158.8230.66.camel@bahia.local> <4DF9F657.7030605@fr.ibm.com>
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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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