netdev - Re: [RESEND net v3] net: ip_tunnel: fix mtu calculation

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Message-ID: <CAM_iQpVu7duRR=KXp8F209qdKj7W6u02icATdRcMtL5Rh8Sv-A@mail.gmail.com>
Date:   Fri, 29 Jan 2021 16:28:52 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Slava Bacherikov <mail@...va.cc>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [RESEND net v3] net: ip_tunnel: fix mtu calculation

On Fri, Jan 29, 2021 at 2:30 PM Vadim Fedorenko <vfedorenko@...ek.ru> wrote:
>
> dev->hard_header_len for tunnel interface is set only when header_ops
> are set too and already contains full overhead of any tunnel encapsulation.
> That's why there is not need to use this overhead twice in mtu calc.
>
> Fixes: fdafed459998 ("ip_gre: set dev->hard_header_len and dev->needed_headroom properly")
> Reported-by: Slava Bacherikov <mail@...va.cc>
> Signed-off-by: Vadim Fedorenko <vfedorenko@...ek.ru>

I have no objection, just please double check this does not break
other IP tunnels as you touch the core ip tunnel code, especially
those using ip_tunnel_header_ops.

Thanks.