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

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Date:   Tue, 17 Apr 2018 16:15:57 -0400
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC net-next 00/11] udp gso

On (04/17/18 16:00), Willem de Bruijn wrote:
> 
> This patchset implements GSO for UDP. A process can concatenate and
> submit multiple datagrams to the same destination in one send call
> by setting socket option SOL_UDP/UDP_SEGMENT with the segment size,
> or passing an analogous cmsg at send time.
> 
> The stack will send the entire large (up to network layer max size)
> datagram through the protocol layer. At the GSO layer, it is broken
> up in individual segments. All receive the same network layer header
> and UDP src and dst port. All but the last segment have the same UDP
> header, but the last may differ in length and checksum.

I'll go through the patch-set later today/tomorrow (interesting!), 
but a question: what are message boundary semantics in this model? E.g.,
if I do a udp_sendmsg of 2000 bytes, and then then a udp_sendmsg of
512 bytes, with the receiver first recvmsg 2000 bytes and then the
512 bytes?

My understanding of the comment above is that no, it will not- 
because (assuming an mtu of 1500) there will be 2 UDP messages on 
the wire, the first one with 1500 bytes, and the second with 1012
bytes (with some discounts for the various L2/L3 etc headers)

--Sowmini