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Date: Fri, 1 Dec 2000 00:15:45 +0000 (GMT)
From: Ben Mansell <ben@zeus.com>
To: "David S. Miller" <davem@redhat.com>
cc: <ak@suse.de>, <linux-kernel@vger.kernel.org>
Subject: Re: TCP push missing with writev()
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On Thu, 30 Nov 2000, David S. Miller wrote:

> 	       vector[ 1 ].iov_base = NULL;
> 	       vector[ 1 ].iov_len = 0;
>
> "Don't do that" :-)
>
> I'll doubt I will bother to fix it (it's not %100 trivial to fix and
> it will put a cost into a hot path).  Even if I did, you're going to
> need to fix Zeus not to do writev's with empty iovec's like this so
> that you get the PSH's in current kernels.

Its OK, our web server currently doesn't have this problem :)

I ran into the problem developing code that wrote data out of a circular
buffer - so the data being written may potentially be in two sections if
the buffer wraps around. A generic writev() call then emptied as much data
out of the buffer as possible, and so tripping the bug. I guess what I'm saying
is that you don't have to have plain dumb code (like the example code I
gave) in order to hit this problem.

Paranoia check: can this bug occur with writev() and other combinations of
sizes, or is it only when there is a 0-length buffer in there?


Ben

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