netdev - Re: [PATCH RFC net-next 00/11] udp gso

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Message-ID: <CAF=yD-+iT55h_QbQNR6RWa0R41N=3GCr+71+qr32GW=1oEc0Hg@mail.gmail.com>
Date:   Wed, 18 Apr 2018 09:59:11 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC net-next 00/11] udp gso

> One thing that was not clear to me about the API: shouldn't UDP_SEGMENT
> just be automatically determined in the stack from the pmtu? Whats
> the motivation for the socket option for this? also AIUI this can be
> either a per-socket or a per-packet option?

I decided to let the application explicitly set segment size, to avoid
bugs from the application assuming a different MTU from the one
used in the kernel for segmentation.

With path MTU, it is too easy for a process to incorrectly assume
link MTU or stale path MTU. With the current interface, if a process
tries to assemble segments larger than relevant path MTU, the
send call will fail.

A process may also explicitly want to send a chain of packets
smaller than MTU.