Re: [PATCH] [RFC] fs, proc: don't guard /proc/<pid>/task/<tid>/children on CONFIG_CHECKPOINT_RESTORE

On Thu, May 21, 2015 at 11:47 PM, Andy Lutomirski [off-list ref] wrote:

On Thu, May 21, 2015 at 3:30 AM, Alban Crequy [off-list ref] wrote:

quoted

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

Thanks for the pointer, I didn't see it.

See also:

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

Your paragraph seems good to have in the documentation but I am also
not qualified to comment on the behavior.