On Wed, Sep 24, 2014 at 9:01 AM, Cong Wang [off-list ref] wrote:

And clearly you missed my question above: how do you get netns id
without sharing /var/run/netns/ ?

OK, I found it:

Ids are stored in the parent user namespace. These ids are valid only inside
this user namespace. The user can retrieve these ids via a new netlink messages,
but only if peer netns are in the same user namespace.

So your example is confusing, perhaps you need some other way to show the ID's
instead of binding to ip netns output which is basically ls
/var/run/netns/. We don't
want an inner netns know anything outside, IOW, we don't share /var/run/netns/.
I think in this case your ID's are still available, but aren't you
providing a new way
for the inner netns device to escape which we are trying to avoid?