netdev - Re: UDP splice

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Date:	Mon, 24 Jun 2013 17:51:54 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Ricardo Landim <ricardolan@...il.com>, netdev@...r.kernel.org
Subject: Re: UDP splice

On Mon, Jun 24, 2013 at 04:42:34PM +0100, Ben Hutchings wrote:
> On Fri, 2013-06-21 at 07:04 -0300, Ricardo Landim wrote:
> > Hi folks,
> > 
> > I am developing a RTP proxy for voip applications and tried use the
> > splice syscall
> > for zero copy. I am trying splice udp data to pipe and splice pipe to udp
> > socket.
> > 
> > I read some information of the splice function and reading the kernel
> > source code I saw this lines in net/ipv4/af_inet.c
> > 
> > const struct proto_ops inet_stream_ops = {
> > ...
> >     .splice_read = tcp_splice_read,
> > ...
> > }
> > 
> > const struct proto_ops inet_dgram_ops = {
> > ...
> > ...
> > }
> > 
> > There is an implementation of splice for TCP socket but not for UDP socket.
> > 
> > My question is: there is some limitation in UDP socket that prevents this
> > implementation?
> 
> splice() works with streams, but UDP is a message-oriented protocol.
> How would a UDP implementation of splice() decide where to put the
> message boundaries, or to distinguish the messages?

Splicing a pipe to udp socket should work nontheless. Splicing from udp socket
to pipe does not work.

Greetings,

  Hannes
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