Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

From: Nicolas Dichtel
Date: Thu Sep 25 2014 - 04:53:45 EST

Le 24/09/2014 18:45, Cong Wang a Ãcrit :
On Wed, Sep 24, 2014 at 9:27 AM, Nicolas Dichtel
<nicolas.dichtel@xxxxxxxxx> wrote:
Now informations got with 'ip link' are wrong and incomplete:
- the link dev is now tunl0 instead of eth0, because we only got an
from the kernel without any netns informations.

This is not new, macvlan has the same problem. This is why I said
it is mostly a display problem, maybe just mark the ifindex as -1 or
something when it is not in this netns. At least I don't expect the inner
netns know anything outside, and I don't think I am the only one using
netns in this way.
I understand your point but there is several use of netns. Netns can be used
also to instantiate virtual routers. In this case, administrators or daemons
need to be able to monitor and dump the configuration on all netns
(particularly beeing able to identify fully x-netns interfaces). We start to
discuss this in one of the two thread pointed in my cover letter and get the
conclusion that checking user ns is a good way to know if an id should be
disclosed or not for a peer netns.
Can you describe your use case?

- the encapsulation addresses are not part of this netns but the user
known that (still because netns info is missing). These IPv4 addresses
exist into this netns.

I don't remember your x-netns code, but we have two choices:

1) Lookup the route of the netns which it is in

If the address is not available in this netns, it will fail, this is expected
since tunnel device is not a pure L2 device. Or maybe just fail
early when we move it.

2) Lookup the route of the netns where it was created

Transparent for upper layer, but as you said, the outer address is not
available in this netns therefore hard to display. Just hiding this information
doesn't seem wrong to me.
Your assumption here is that all dameons were started before the tunnel was
created. But this is not true, a daemon may be started later. Another case is
when a daemon crash: we need to be able to restart it and it should be able to
recover all needed information.

- it's not possible to create the same netdevice with these infos.

This is expected, because after all you are already in a different netns.

A different netns only means a different network stack, not a different user ns
or mount ns or PID ns, ...
If you only play with netns, you may want to monitor all activies in all netns
(this is already possible) and beeing able to link information between netns
(this is what I'm trying to solve).
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