netdev - Re: [PATCH] net: vxlan: disallow removing to other namespace

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Date:   Tue, 21 May 2019 13:53:04 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: vxlan: disallow removing to other namespace

On Tue, May 21, 2019 at 7:53 AM David Miller <davem@...emloft.net> wrote:
>
> From: xiangxia.m.yue@...il.com
> Date: Fri, 17 May 2019 19:42:23 -0700
>
> > From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> >
> > Don't allow to remove the vxlan device to other namesapce,
> > because we maintain the data of vxlan net device on original
> > net-namespace.
> >
> >     $ ip netns add ns100
> >     $ ip link add vxlan100 type vxlan dstport 4789 external
> >     $ ip link set dev vxlan100 netns ns100
> >     $ ip netns exec ns100 ip link add vxlan200 type vxlan dstport 4789 external
> >     $ ip netns exec ns100 ip link
> >     ...
> >     vxlan200: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
> >     vxlan100: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
> >
> > And we should create it on new net-namespace, so disallow removing it.
> >
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
>
> I don't understand this change at all.
>
> You keep saying "Remove" but I think you might mean simply "Move" because
> the NETNS_LOCAL flag prevents moving not removing.
Yes, should change "remove" to "move".

> And why is it bad to allow vxlan devices to be moved between network
> namespaces?  What problem would it cause and can you guarantee that
> you are not breaking an existing user?

The problem is that we create one vxlan netdevice(e.g dstport 4789 and
external), and move it to
one net-namespace, and then we hope create one again(dstport 4789 and
external) and move it to other net-namespace, but we can't create it.

$ ip netns add ns100
$ ip link add vxlan100 type vxlan dstport 4789 external
$ ip link set dev vxlan100 netns ns100
$ ip link add vxlan200 type vxlan dstport 4789 external
RTNETLINK answers: File exists

The better way is that we should create directly it in the
net-namespace. To avoid confuse user, disallow moving it to other
net-namespace.

> I'm not applying this as-is.