netdev - Re: UDP splice

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Message-ID: <1372088554.1896.3.camel@bwh-desktop.uk.level5networks.com>
Date:	Mon, 24 Jun 2013 16:42:34 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Ricardo Landim <ricardolan@...il.com>
CC:	<netdev@...r.kernel.org>
Subject: Re: UDP splice

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?

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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