netdev - Re: [RFC 0/2] Delayed binding of UDP sockets for Quic per-connection sockets

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Message-ID: <CAF=yD-+0ASe9xjzLg2cde=E5XfCRhCKboAaMSr08Q3eQFL4vNg@mail.gmail.com>
Date:   Thu, 1 Nov 2018 17:51:39 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     cpaasch@...le.com
Cc:     Network Development <netdev@...r.kernel.org>, ianswett@...gle.com,
        lhedstrom@...le.com, jri.ietf@...il.com,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [RFC 0/2] Delayed binding of UDP sockets for Quic per-connection sockets

On Wed, Oct 31, 2018 at 7:30 PM Christoph Paasch <cpaasch@...le.com> wrote:
>
> Implementations of Quic might want to create a separate socket for each
> Quic-connection by creating a connected UDP-socket.
>
> To achieve that on the server-side, a "master-socket" needs to wait for
> incoming new connections and then creates a new socket that will be a
> connected UDP-socket. To create that latter one, the server needs to
> first bind() and then connect(). However, after the bind() the server
> might already receive traffic on that new socket that is unrelated to the
> Quic-connection at hand.

This can also be achieved with SO_REUSEPORT_BPF and a filter
that only selects the listener socket(s) in the group. The connect
call should call udp_lib_rehash and take the connected socket out
of the reuseport listener group. Though admittedly that is more
elaborate than setting a boolean socket option.

> The ideas for the implementation came up after a discussion with Ian
> and Jana re: their implementation of a QUIC server.

That might have preceded SO_TXTIME? AFAIK traffic shaping was the
only real reason to prefer connected sockets.