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

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Date:   Mon, 23 Nov 2020 10:40:47 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin Schiller <ms@....tdt.de>
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 Mon, 23 Nov 2020 07:18:07 +0100 Martin Schiller wrote:
> 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

Thanks for this info, applied to net-next.