linux-kernel - Re: [PATCH 0/2] Fix /proc/net in presence of net namespaces

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Date:	Mon, 03 Mar 2008 11:52:49 +0300
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Alexey Dobriyan <adobriyan@...nvz.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Fix /proc/net in presence of net namespaces

Eric W. Biederman wrote:
> Pavel Emelyanov <xemul@...nvz.org> writes:
> 
>> I could use the struct net pointer values (obtained with sprintf(id, "%p", net))
>> instead, but exporting internal kernel addresses seemed even uglier.
> 
> Agreed.
> 
>>> Can you try this approach by capturing a struct pid instead of an id
>>> in a new global namespace? 
>> This is a bad approach. When task, that created the namespace dies, his
>> pid is removed from the pidmap and can be reused, so we can get another
>> net with the same id.
> 
> It takes a little updating of how we use pids.  The easiest method
> is to add an extra counter.  So we know when someone besides the hash
> chains is using the pid as an id.  However it might make sense to actually
> have a net namespace pointer in the pid.

No, please, no. I'm strongly opposed to making pids provide identification
for anything we need in the kernel.

>> This net's id is not supposed to be used to address any net in the kernel.
>> And I see no problems with migration - you can change the net's id safely
>> during checkpoint/restart - tasks will always see this one via the /proc/net
>> symlink, which is dynamic.
> 
> So you are really talking about a hidden id.  There are just enough
> ways for something like that to slip out I'm not especially
> comfortable with the idea.
> 
> I really think we need something clean that we can live with, and be
> proud of.  However we implement the enhancement to /proc/net this has
> to be maintained for decades.
> 
> Eric
> 

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