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

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Date:	Wed, 24 Sep 2014 11:23:19 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Cong Wang <cwang@...pensource.com>
CC:	netdev <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, David Miller <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

Le 23/09/2014 21:22, Cong Wang a écrit :
> On Tue, Sep 23, 2014 at 6:20 AM, Nicolas Dichtel
> <nicolas.dichtel@...nd.com> wrote:
>>
>> Here is a small screenshot to show how it can be used by userland:
>> $ ip netns add foo
>> $ ip netns del foo
>> $ ip netns
>> $ touch /var/run/netns/init_net
>> $ mount --bind /proc/1/ns/net /var/run/netns/init_net
>> $ ip netns add foo
>> $ ip netns
>> foo (id: 3)
>> init_net (id: 1)
>> $ ip netns exec foo ip netns
>> foo (id: 3)
>> init_net (id: 1)
>> $ ip netns exec foo ip link add ipip1 link-netnsid 1 type ipip remote 10.16.0.121 local 10.16.0.249
>> $ ip netns exec foo ip l ls ipip1
>> 6: ipip1@...E: <POINTOPOINT,NOARP> mtu 1480 qdisc noop state DOWN mode DEFAULT group default
>>      link/ipip 10.16.0.249 peer 10.16.0.121 link-netnsid 1
>>
>> The parameter link-netnsid shows us where the interface sends and receives
>> packets (and thus we know where encapsulated addresses are set).
>>
>
> So ipip1 is shown in netns foo but functioning in netns init_net? Getting the
> id of init_net in foo depends on your mount namespace, /var/run/netns/ may
> not visible inside foo, in this case, link-netnsid is meaningless. It
> is not your
> fault, network namespace already heavily relies on mount namespace (sysfs
> needs to be remount otherwise you can not create device with the same name.)
>
> On the other hand, what's the problem you are trying to solve? AFAIK,
> the ifindex
> issue is purely in output, IOW, the device still functions correctly
> even through
> its link ifindex is not correct after moving to another namespace. If
> not, it is bug
> we need to fix.
>
The problem is explained here:
http://thread.gmane.org/gmane.linux.network/315933/focus=316064
and here:
http://thread.gmane.org/gmane.linux.kernel.containers/28301/focus=4239


Regards,
Nicolas
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