linux-kernel - Re: [PATCH 1/1] ftrace: fix wrong pos computing when read buffer has been fulfilled.

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Date:	Tue, 18 Nov 2008 16:52:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	walimis <walimisdev@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ftrace: fix wrong pos computing when read buffer
	has been fulfilled.


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Tue, 18 Nov 2008, walimis wrote:
> > On Tue, Nov 18, 2008 at 09:36:07AM -0500, Steven Rostedt wrote:
> > >> 
> > >> fix:
> > >> 
> > >> Through checking return value of seq_printf, if less than 0, we know
> > >> this function doesn't be printed. Then we decrease position to force
> > >> this function to be printed next time, in next read buffer.
> > >
> > >A lot of the code for seq files I cut and paste from other places that I 
> > >have written it. The seq files always confuse me, so I like to use stuff 
> > >that worked before. Some of the things that walimis fixed were not needed 
> > >for this file, and was overkill.
> 
> > It also confuse me a lot. I also checked all places using seq files in
> > trace/ftrace code, to see whether there are similar problem.
> >   - trace.c: in s_start() it force pos to decrease one such as: 
> > 	l = *pos - 1;
> > 	so it works well.
> >   - trace_stack.c: t_start, in almost all cases, can be only called
> >     once, so we don't see the error. But I wonder whether it still works
> >     well if output message exceeds the size of seq file buffer and call
> >     t_start twice. If needed, I can test it.
> >   - trace_branch.c : the same with above.
> > 
> 
> If you can find a bug, then by all means, fix it ;-)

also, if you can think of a way to structure the code in a cleaner way 
to make such mistakes less likely to occur, feel free to change that 
too.

	Ingo
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