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

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Date:	Wed, 24 Sep 2014 09:01:05 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.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

On Wed, Sep 24, 2014 at 2:23 AM, Nicolas Dichtel
<nicolas.dichtel@...nd.com> wrote:
> 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
>

Please, summarize the discussion in your changelog, instead of pointing
to a long thread.

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