From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Subject: Re: [PATCH] [RFC] fs, proc: don't guard /proc/<pid>/task/<tid>/children
 on CONFIG_CHECKPOINT_RESTORE
Date: Thu, 21 May 2015 14:47:33 -0700
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To: Alban Crequy <alban.crequy-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Cyrill Gorcunov <gorcunov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Pavel Emelyanov <xemul-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, Serge Hallyn <serge.hallyn-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Linux FS Devel <linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Alban Crequy <alban-973cpzSjLbNWk0Htik3J/w@public.gmane.org>, Iago Lopez Galeiras <iago-973cpzSjLbNWk0Htik3J/w@public.gmane.org>
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On Thu, May 21, 2015 at 3:30 AM, Alban Crequy <alban.crequy-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> From: Alban Crequy <alban-973cpzSjLbNWk0Htik3J/w@public.gmane.org>
>
> commit 818411616baf ("fs, proc: introduce
> /proc/<pid>/task/<tid>/children entry") introduced the children entry
> for checkpoint restore and the file is only available on kernels
> configured with CONFIG_EXPERT and CONFIG_CHECKPOINT_RESTORE.
>
> This is available in most distributions (Fedora, Debian, Ubuntu, CoreOS)
> because they usually enable CONFIG_EXPERT and CONFIG_CHECKPOINT_RESTORE.
> But Arch does not enable CONFIG_EXPERT or CONFIG_CHECKPOINT_RESTORE.
>
> However, the children proc file is useful outside of checkpoint restore.
> I would like to use it in rkt. The rkt process exec() another program it
> does not control, and that other program will fork()+exec() a child
> process. I would like to find the pid of the child process from an
> external tool without iterating in /proc over all processes to find
> which one has a parent pid equal to rkt.
>
> Since the children proc file is useful outside of checkpoint-restore,
> I am removing the guard on CONFIG_CHECKPOINT_RESTORE.

I sent an essentially identical patch a couple years ago, and it got
some interesting comments:

http://lkml.kernel.org/g/0e00e9073855c02a382d49ba1ede9c4fda3451b7.1372189875.git.luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org

See also:

http://lkml.kernel.org/g/5f9a6b3ab75b12f2c5ba61ea1f6f3b08e9952b55.1372280661.git.luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org

--Andy