linux-kernel - Re: [PATCH] splice: fix problem with sys_tee and SPLICE_F

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Date:	Tue, 19 Feb 2008 22:47:41 +0100
From:	Johann Felix Soden <johfel@....de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Johann Felix Soden <johfel@....de>,
	Patrick McManus <mcmanus@...ksong.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] splice: fix problem with sys_tee and SPLICE_F_NONBLOCK


Am Dienstag, den 19.02.2008, 22:25 +0100 schrieb Jens Axboe:
> On Tue, Feb 19 2008, Johann Felix Soden wrote:
> > > On Tue, Feb 19 2008, Johann Felix Soden wrote:
> > > > From: Johann Felix Soden <johfel@...rs.sourceforge.net>
> > > > 
> > > > With SPLICE_F_NONBLOCK sys_tee should return number of duplicated bytes,
> > > > not only -EAGAIN on success.
> > > 
> > > ?
> > > 
> > > The current behaviour is to return bytes tee'd, or return -EAGAIN for
> > > zero bytes if SPLICE_F_NONBLOCK is set. It doesn't return "-EAGAIN on
> > > success", not sure what you mean there.
> > > 
> > Sorry, my patch description was not correct. 
> > 
> > The new behavior of sys_tee with my patch is: 
> > 	- return -EAGAIN if there are no data in the pipe, but writer
> > 	  connected to the pipe, 
> > 	- return 0 if there are not writers connected
> > 	- else return number of duplicated byte 
> > 
> > The old behavior was: return -EAGAIN or the number (>0) of duplicated
> > bytes.
> 
> Your patch has an odd way of achieving that goal, modify the real
> location of the assignment instead of overriding something. That has the
> potential to turn into another confusing bug later on, wondering why the
> heck your return value isn't being passed back.
> 
> Improvement is welcome though, you can't distuingish -EAGAIN on the
> input side from the output side currently.
> 

I thought again about the problem and my patch: you are right, the patch
is nonsense. I have learnt, that the correctness of a patch is not
guaranteed by the (bad, but anyhow working) solution of the problem the
patch was written for.
Sorry for wasting your time.
--
 J. F. Soden


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