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Date: Mon, 26 May 2014 22:04:43 +0400
From: Vasily Kulikov <segooon@gmail.com>
To: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>
Cc: containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Serge Hallyn <serge.hallyn@ubuntu.com>,
        Oleg Nesterov <oleg@redhat.com>, David Howells <dhowells@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] /proc/pid/status: show all sets of pid according to ns
Message-ID: <20140526180443.GA11145@cachalot>
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Hi Chen,

On Mon, May 26, 2014 at 18:05 +0800, Chen Hanxiao wrote:
> We need a direct method of getting the pid inside containers.
> If some issues occurred inside a container guest, host user
> could not know which process is in trouble just by guest pid:
> the users of container guest only knew the pid inside containers.
> This will bring obstacle for trouble shooting.
> 
> This patch expands fields of Tgid and Pid:
> a) In init_pid_ns, nothing changed;
> 
> b) In one pidns, they will tell the pid inside containers:
> Tgid:	1628 	9 	3
> Pid:	1628 	9 	3
> ** process id is 1628 in level 0, 9 in level 1, 3 in level 2.

1. It breaks ABI.  Any application which does something like "grep pid: | cut -d: -f2"
is now broken by the patch.  Maybe add a new field like 'Pid-ns', 'PidNS',
or 'Pids' and leave the old one for compatibility?

2. Is it OK to show internal pids to unprivileged processes?  I cannot
see anything obviously dangerous with it, though.

> c) If pidns is nested, it depends on which pidns are you in.
> Tgid:	9 	3
> Pid:	9 	3
> ** Views from level 1 for Pid 1628 in host.

-- 
Vasily