netdev - Re: [PATCH v2 net 3/3] wireguard: send: account for mtu=0 devices

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Message-ID: <CAHmME9pjLfscZ-b0YFsOoKMcENRh4Ld1rfiTTzzHmt+OxOzdjA@mail.gmail.com>
Date:   Fri, 14 Feb 2020 19:15:26 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 net 3/3] wireguard: send: account for mtu=0 devices

On Fri, Feb 14, 2020 at 6:56 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
> Oh dear, can you describe what do you expect of a wireguard device with mtu == 0 or mtu == 1
>
> Why simply not allowing silly configurations, instead of convoluted tests in fast path ?
>
> We are speaking of tunnels adding quite a lot of headers, so we better not try to make them
> work on networks with tiny mtu. Just say no to syzbot.

The idea was that wireguard might still be useful for the persistent
keepalive stuff. This branch becomes very cold very fast, so I don't
think it makes a difference performance wise, but if you feel strongly
about it, I can get rid of it and set a non-zero min_mtu that's the
smallest thing wireguard's xmit semantics will accept. It sounds like
you'd prefer that?