netdev - Re: [PATCH] Make /proc/net a symlink on /proc/self/net (v2)

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Message-ID: <m1od9r26bu.fsf@ebiederm.dsl.xmission.com>
Date:	Thu, 06 Mar 2008 08:57:41 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] Make /proc/net a symlink on /proc/self/net (v2)

Pavel Emelyanov <xemul@...nvz.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@...nvz.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
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