linux-kernel - Re: [PATCH 1/3] relay: Fix 4 off-by-one errors occuring when writing to a CPU buffer.

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Message-ID: <20080730174821.GA5222@localhost>
Date:	Wed, 30 Jul 2008 20:48:21 +0300
From:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
To:	Tom Zanussi <tzanussi@...il.com>
Cc:	penberg@...helsinki.fi, akpm@...ux-foundation.org,
	compudj@...stal.dyndns.org, linux-kernel@...r.kernel.org,
	righi.andrea@...il.com
Subject: Re: [PATCH 1/3] relay: Fix 4 off-by-one errors occuring when
	writing to a CPU buffer.

On Thu, Jul 24, 2008 at 12:09:36AM -0500, Tom Zanussi wrote:
> 
> On Sat, 2008-06-21 at 05:06 +0300, Eduard - Gabriel Munteanu wrote:
> > On Mon, 16 Jun 2008 00:22:27 -0500
> > Tom Zanussi <tzanussi@...il.com> wrote:
> > 
> > > So apparently what you're seeing is zeroes being read when there's a
> > > buffer-full condition?  If so, we need to figure out exactly why
> > > that's happening to see whether your fix is really what's needed; I
> > > haven't seen problems in the buffer-full case before and I think your
> > > fix would break it even if it fixed your read problem.  So it would
> > > be good to be able to reproduce it first.
> > > 
> > > Tom  
> > 
> > Hi,
> > 
> > Sorry for being so late, there were some exams I had to cope with.
> > 
> > Although I couldn't reproduce zeros, I've come up with something I'd
> > say is equally good. This has been done on a vanilla 2.6.26-rc6.
> > 
> > Please look at the testcase below and tell me what you think.
> > 
> 
> Hi,
> 
> Yes, this is a bug - thanks for sending the nice test case.  This patch
> should fix it.  BTW, if the output still looks a little different from
> what you were expecting, it might make more sense after adding a
> relay_test printk for each dropped event, something like this:

The all-zeros problem happened when poll() with infinite timeout is not
used before reading. I fixed the user app I was writing, but the docs should
really reflect this. Relay has a kinda strange interface.


	Cheers,
	Eduard

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