linux-kernel - Re: Honoring SO_RCVLOWAT in proto

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Message-ID: <20080921151811.46328133@lxorguk.ukuu.org.uk>
Date:	Sun, 21 Sep 2008 15:18:11 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	lkml@...garu.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Honoring SO_RCVLOWAT in proto_ops.poll methods

> > You might also want to look at the socket(7) man page which implies that
> > what Linux currently does is exceptional & incorrect:

Actually we follow 1003.1g draft 6.4 which is about as close as there
ever was a spec for BSD sockets. We go beyond it actually -
SO_RCVLOWAT/SO_SNDLOWAT are in fact optional.

> SO_RCVLOWAT, and to my surprise even my recv() calls with MSG_PEEK flags
> set are not blocking.  They block without MSG_PEEK, but not with.

Correct and we've always done that intentionally.

> At this point, for my application to work on Linux without burning CPU like
> mad... I basically have to sleep and poll the socket regularly to see if
> more data has arrived with the tcp socket ioctl SIOCINQ. :(

What are you actually trying to do ? The usual way to handle urgent data
in those odd cases that use it is to select for an exception event.

Alan
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