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

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Message-Id: <20190520.195319.201742803310676769.davem@davemloft.net>
Date:   Mon, 20 May 2019 19:53:19 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     xiangxia.m.yue@...il.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] net: vxlan: disallow removing to other namespace

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.

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?

I'm not applying this as-is.