Return-Path: <linux-kernel-owner+w=401wt.eu-S933274AbYCFQDz@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S933274AbYCFQDz (ORCPT <rfc822;w@1wt.eu>);
	Thu, 6 Mar 2008 11:03:55 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759294AbYCFQDn
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Thu, 6 Mar 2008 11:03:43 -0500
Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:41874 "EHLO
	ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757452AbYCFQDm (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 6 Mar 2008 11:03:42 -0500
From: ebiederm@xmission.com (Eric W. Biederman)
To: Pavel Emelyanov <xemul@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       David Miller <davem@davemloft.net>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Netdev List <netdev@vger.kernel.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] Make /proc/net a symlink on /proc/self/net (v2)
References: <47CFB6CA.8090001@openvz.org>
Date: Thu, 06 Mar 2008 08:57:41 -0700
In-Reply-To: <47CFB6CA.8090001@openvz.org> (Pavel Emelyanov's message of "Thu,
	06 Mar 2008 12:18:02 +0300")
Message-ID: <m1od9r26bu.fsf@ebiederm.dsl.xmission.com>
User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1762
Lines: 43

Pavel Emelyanov <xemul@openvz.org> writes:

> Current /proc/net is done with so called "shadows", but current
> implementation is broken and has little chances to get fixed.
>
> The problem is that dentries subtree of /proc/net directory has
> fancy revalidation rules to make processes living in different
> net namespaces see different entries in /proc/net subtree, but
> currently, tasks see in the /proc/net subdir the contents of any
> other namespace, depending on who opened the file first.
>
> The proposed fix is to turn /proc/net into a symlink, which points
> to /proc/self/net, which in turn shows what previously was in
> /proc/net - the network-related info, from the net namespace the
> appropriate task lives in.
>
> # ls -l /proc/net
> lrwxrwxrwx  1 root root 8 Mar  5 15:17 /proc/net -> self/net
>
> In other words - this behaves like /proc/mounts, but unlike
> "mounts", "net" is not a file, but a directory.
>
> Fixed a task_struct leak in get_proc_task_net, pointed out by Paul.
>
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

Before I forget.

As a future patch we need to implement a d_revalidate rule for
/proc/<pid>/task/net that will notice we have unshared a network
namespace and flush all cached dentries for the old network namespace.

Since unsharing happens rarely if at all this d_revalidate should
be relatively cheap, and since the change is real and for everyone
it will not suffer from the inconsistencies that plagued us when
working with d_revalidate on /proc/net.

Eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/