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

On Wed, May 18, 2011 at 4:33 PM, David Lamparter [off-list ref] wrote:

On Wed, May 18, 2011 at 04:03:03PM +0300, Alexey Dobriyan wrote:

quoted

On Wed, May 18, 2011 at 3:43 PM, David Lamparter [off-list ref] wrote:

quoted

-   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.

quoted

quoted

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.