netdev - Re: [ABI REVIEW][PATCH 0/8] Namespace file descriptors

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Message-ID: <20100923151853.GC1160234@jupiter.n2.diac24.net>
Date:	Thu, 23 Sep 2010 17:18:53 +0200
From:	David Lamparter <equinox@...c24.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org,
	Linux Containers <containers@...ts.osdl.org>,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, jamal <hadi@...erus.ca>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Ulrich Drepper <drepper@...il.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	David Miller <davem@...emloft.net>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Ben Greear <greearb@...delatech.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Jonathan Corbet <corbet@....net>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [ABI REVIEW][PATCH 0/8] Namespace file descriptors

On Thu, Sep 23, 2010 at 01:45:04AM -0700, Eric W. Biederman wrote:
> Introduce file for manipulating namespaces and related syscalls.
> files:
> /proc/self/ns/<nstype>

As feedback from using network namespaces extensively in more or less
production setups, I would like to make a request/suggestion: there
needs to be a way to enumerate network namespaces independent from
by-pid access.

At several occasions, I was left with either some runaway daemon which
kept the namespace alive. To describe this a little more graphically:
I found no other way than doing a
	md5sum /proc/*/net/if_inet6 | sort | uniq -c -w 32
to find out which runaway to kill to terminate the namespace.

This makes network namespaces particularly cumbersome to use without PID
namespaces. While I agree that a large part of the users - namely lxc -
will use them together, network namespaces without pidns are very
interesting for routing applications implementing VRFs.

Is it possible to add some kind of "all namespaces" list, optimally
giving an opportunity to open() exactly this file descriptor that you
get from /proc/<pid>/ns/net?

Also, is it possible to extend that file descriptor to have an
"get all pids" ioctl,
...or, wait, maybe have /proc/...ns/proc/<pid> symlink?

(This obviously isn't fully thought to the end, please pick up...)

-David

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