Date: Wed, 07 Feb 2001 10:51:45 -0700 From: Wes Peters <wes@softweyr.com> To: Alfred Perlstein <bright@wintelcom.net> Cc: Luigi Rizzo <rizzo@aciri.org>, net@FreeBSD.ORG Subject: Re: send problem on udp socket... Message-ID: <3A818B31.9B12C8B3@softweyr.com> References: <200102071714.f17HEDH75274@iguana.aciri.org> <20010207093731.N26076@fw.wintelcom.net>
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Alfred Perlstein wrote:
>
> * Luigi Rizzo <rizzo@aciri.org> [010207 09:14] wrote:
> > Hi,
> >
> > just occurred to me that there exists the following feature of
> > send/sendmsg and probably also write on UDP sockets, and it would
> > be worth documenting.
>
> Yes it is.
>
> [snip]
> > When you attempt to send() to an udp socket, the socket buffer
> > (which has no function other than bounding the max message size
> > for UDP sockets) is just bypassed, and the low-level routine gets
> > called. The latter (typically ip_output() or ether_output()) can
> > return an ENOBUFS message if some queue fills up down there (typically
> > the interface queue), and the error message is passed up.
> >
> > Now, the send() manpage is technically correct as it only
> > mentions the socket buffer full as the reason for blocking,
> > but in my opinion the above is not _that_ obvious and it would
> > be worth documenting.
> >
> > As a matter of fact, i wonder if it would be a good idea to
> > try and improve this behaviour by letting sosend() do a tsleep()
> > on the device/subsystem reporting the failure, and have the
> > latter issue a wakeup when space frees again. The only thing
> > is, i believe this has some odd ramifications with handling
> > select/poll, and might break some software that does not
> > handle blocking send() on UDP sockets.
>
> ENOBUFS == ESYSADMINNEEDSTORAISENMBCLUSTERS
Or perhaps ENOBUFS == E_SYSTEM_NEEDS_TO_RAISE_NMBCLUSTERS_ALL_ON_ITS_OWN?
A starting point, increment, and ceiling, based on the memory size of the
system, might be a more reasonable design for a lot of these hard-coded
parameters left over from the days of the VAX 750.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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