From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?iso-8859-1?q?R=E9mi_Denis-Courmont?= <rdenis@simphalempin.com>
Subject: Re: [PATCH] sendfile() and UDP socket
Date: Thu, 18 Sep 2008 20:31:00 +0300
Message-ID: <200809182031.01291.rdenis@simphalempin.com>
References: <1221387956.9204.7.camel@fry> <20080916.210117.31865904.taka@valinux.co.jp>
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To: Hirokazu Takahashi <taka@valinux.co.jp>, johaahn@gmail.com
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Le mardi 16 septembre 2008 15:01:17 Hirokazu Takahashi, vous avez =E9cr=
it=A0:
> UDP is a datagram protocol, so I think applications using UDP should
> care about the size of packets they are going to send rather than
> expecting that the messages will be split into several packets
> automatically. If some of the packets have lost, it will be really ha=
rd for
> the applications to re-create the same ones to send again.

Also, why use UDP for this... If you want stream semantics, why not use=
 TCP or=20
SCTP instead?

> If you want send a large file over UDP, the typical code will be like=
:

> while (...) {
>         sendmsg(fd, &apl_header, sizeof(apl_header), MSG_MORE);
>         offset +=3D sendfile(fd, offset, count);
> }

Correct me if I am wrong, but... Unless you have a big MTU (as _not_ in=
 1500=20
bytes :D), doing an extra syscall might be slower than copying data in =
a=20
single vectorized sendmsg() syscall.

--=20
R=E9mi Denis-Courmont
http://www.remlab.net/