netdev - Re: Identifying network namespaces (was: Network namespace manipulation with file descriptors)

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Message-ID: <BANLkTinx1i3UJ86xw8KdvF+dQ1-qNZfFtA@mail.gmail.com>
Date:	Wed, 18 May 2011 17:13:05 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	David Lamparter <equinox@...c24.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	jamal <hadi@...erus.ca>, Daniel Lezcano <daniel.lezcano@...e.fr>,
	Linux Containers <containers@...ts.osdl.org>,
	Renato Westphal <renatowestphal@...il.com>
Subject: Re: Identifying network namespaces (was: Network namespace
 manipulation with file descriptors)

On Wed, May 18, 2011 at 4:33 PM, David Lamparter <equinox@...c24.net> wrote:
> On Wed, May 18, 2011 at 04:03:03PM +0300, Alexey Dobriyan wrote:
>> On Wed, May 18, 2011 at 3:43 PM, David Lamparter <equinox@...c24.net> wrote:
>> > -   processes cannot easily be cross referenced with each other
>> >
>> >  in the case of user space stuff running astray - like management
>> >  software crashing, routing daemons screwing up, etc. - it becomes
>> >  fairly difficult to shut down a network namespace (or even reaquire
>> >  physical devices that have been reassigned)
>>
>> It shutdowns itself when last process using netns disappeares,
>> so if you kill your routing daemons you should be fine.
>> Physical netdevices are moved to init_net.
>
> Now assume I'm running pptpd, which forks a new pppd for each
> connection. Even if I kill pptpd, the pppd keeps running... now how do I
> find the pppds that belong to that one namespace that I'm trying to
> get rid of?

That's a valid question.

>> > So, considering this set of premises (feedback welcome) I looked for
>> > some suitable means of identification. I discarded going for any process
>> > identifiers since Eric's patches allow for network namespaces without
>> > any process holding a reference, using bind mounts instead.
>>
>> If anything it should be netns->id, /proc/*/netns outputting id
>> where id is not derived from kernel pointer.

Actually it should be symlink
/proc/net/netns -> 0         # for init_net
/proc/net/netns -> u32 (> 0)   # for the rest
to extract information by 1 syscall, not 3
where netns id is totally random, so userspace won't make assumptions.
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