linux-kernel - Re: [PATCH RESEND 2/2] pidns: Expose task pid_ns_for

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Message-Id: <20170330150520.1bdf20e599ff464bda0776b9@linux-foundation.org>
Date:   Thu, 30 Mar 2017 15:05:20 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     <agruenba@...hat.com>, <keescook@...omium.org>,
        <linux-api@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <viro@...iv.linux.org.uk>, <oleg@...hat.com>,
        <paul@...l-moore.com>, <ebiederm@...ssion.com>,
        <avagin@...nvz.org>, <linux-fsdevel@...r.kernel.org>,
        <mtk.manpages@...il.com>, <luto@...capital.net>,
        <mingo@...nel.org>, <serge@...lyn.com>
Subject: Re: [PATCH RESEND 2/2] pidns: Expose task pid_ns_for_children to
 userspace

On Thu, 30 Mar 2017 13:27:59 +0300 Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> pid_ns_for_children set by a task is known only to the task itself,
> and it's impossible to identify it from outside.
> 
> It's a big problem for checkpoint/restore software like CRIU,
> because it can't correctly handle tasks, that do setns(CLONE_NEWPID)
> in proccess of their work.
> 
> This patch solves the problem, and it exposes pid_ns_for_children
> to ns directory in standard way with the name "pid_for_children":
> 
> ~# ls /proc/5531/ns -l | grep pid
> lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid -> pid:[4026531836]
> lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid_for_children -> pid:[4026532286]
> 
> --- a/fs/proc/namespaces.c
> +++ b/fs/proc/namespaces.c
> @@ -23,6 +23,7 @@ static const struct proc_ns_operations *ns_entries[] = {
>  #endif
>  #ifdef CONFIG_PID_NS
>  	&pidns_operations,
> +	&pidns_for_children_operations,
>  #endif

This interface should be documented somewhere under Documentation/. 
But I can't immediately find where the /proc/pid/ns/ pseudo-files are
documented...