linux-kernel - Re: [PATCH] perf, tool, record: Fix the header generation for pipe

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Date:	Mon, 29 Aug 2011 10:20:37 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, paulus@...ba.org, linux-kernel@...r.kernel.org,
	Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH] perf, tool, record: Fix the header generation for pipe

Em Mon, Aug 22, 2011 at 06:07:13PM +0200, Jiri Olsa escreveu:
> On Mon, Aug 22, 2011 at 05:51:06PM +0200, Eric Dumazet wrote:
> > Le lundi 22 août 2011 à 16:52 +0200, Jiri Olsa a écrit :
> > > - fd is always file.. the descriptor, which might be pipe, is in output_fd variable
> > >   but, maybe the die call is not necessary.. this should not fail

> > > - the record_file function is called only on debugfs or procfs files:
> > > 	events/header_page
> > > 	events/header_event
> > > 	events/**/format
> > > 	printk_formats
> > > 	/proc/kallsyms

> > > so I think I need to read the whole file as in current code.

> > You read the file twice. Is it the right fix ?

> > Once to compute the length to be able to write the output header, once
> > to process the content.

> > Are you sure length cannot change between the two phases ?

> > /proc/kallsyms can definitely change when a module is loaded.

> Right, better to store it to a temp file as you suggest, so we have
> consistent view.. I'll prepare new patch.

Hi Jiri, any news here?

I just stumbled in this bug while testing Neil's net_dropmonitor script
:-\

- Arnaldo
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