From: Mark Hills <mark@pogo.org.uk>
To: linux-kernel@vger.kernel.org
Subject: splice() on unix sockets
Date: Wed, 22 Apr 2009 23:15:07 +0100 (BST) [thread overview]
Message-ID: <alpine.BSO.2.00.0904220913580.19956@zrgural.vwaro.pbz> (raw)
I found that splice() can operate from a pipe to a unix socket, but from a
unix socket to a pipe fails with EINVAL.
On investigation, splicing from a pipe to a unix socket (af_unix.c) gets
routed through a regular unix_stream_sendmsg (via sock_no_sendpage). If my
understanding is correct this means it will copy memory and not
references, so it's not actually a splice.
If so, splice() behaves inconsistently; sometimes it fails on unsupported
file descriptors, sometimes it falls back to a copy. The man page favours
the former, but the latter could also be useful -- to call splice() with
any pair of fds and have the kernel do the best it can.
Splicing between unix sockets and pipes would give a useful performance
benefit. Is there any work in progress on this? Are there any caveats to
implementing it?
Thanks,
--
Mark
reply other threads:[~2009-04-22 23:06 UTC|newest]
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