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

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Message-ID: <CAHA+R7NnBJ=T3sukzzp-OD2am1nd318XbrXCX84LfSL=nu9ojw@mail.gmail.com>
Date:	Tue, 23 Sep 2014 12:22:01 -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 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.
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