linux-kernel - Re: [PATCH net-next v5] net/tun: Call netdev notifiers

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Message-ID: <a00d2725bce23f451cd030b9e621a764@dev.tdt.de>
Date:   Mon, 23 Nov 2020 07:18:07 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5] net/tun: Call netdev notifiers

On 2020-11-20 19:28, Jakub Kicinski wrote:
> On Wed, 18 Nov 2020 07:39:19 +0100 Martin Schiller wrote:
>> Call netdev notifiers before and after changing the device type.
>> 
>> Signed-off-by: Martin Schiller <ms@....tdt.de>
> 
> This is a fix, right? Can you give an example of something that goes
> wrong without this patch?

This change is related to my latest patches to the X.25 Subsystem:
https://patchwork.kernel.org/project/netdevbpf/list/?series=388087

I use a tun interface in a XoT (X.25 over TCP) application and use the
TUNSETLINK ioctl to change the device type to ARPHRD_X25.
As the default device type is ARPHRD_NONE the initial NETDEV_REGISTER
event won't be catched by the X.25 Stack.

Therefore I have to use the NETDEV_POST_TYPE_CHANGE to make sure that
the corresponding neighbour structure is created.

I could imagine that other protocols have similar requirements.

Whether this is a fix or a functional extension is hard to say.

Some time ago there was also a corresponding patch for the WAN/HDLC
subsystem:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=2f8364a291e8