linux-kernel - Re: [PATCH] perf_event: mount debugfs automatically

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Message-ID: <4B386615.7000207@cn.fujitsu.com>
Date:	Mon, 28 Dec 2009 16:02:29 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Clark Williams <williams@...hat.com>,
	John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH] perf_event: mount debugfs automatically



Ingo Molnar wrote:
> * Xiao Guangrong <xiaoguangrong@...fujitsu.com> wrote:
> 
>> Mount debugfs automatically if it's not mounted, umount it
>> when programme exit
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
>> ---
>>  tools/perf/perf.c         |   10 +++++++++-
>>  tools/perf/util/debugfs.c |   16 +++++++---------
>>  tools/perf/util/debugfs.h |    2 +-
>>  3 files changed, 17 insertions(+), 11 deletions(-)
> 
> I'm not sure that's a good idea. What happens if two perf tools are running in 
> parallel:
> 
>   perf report #1 start
>                           perf report #2 start
>   perf report #2 exit [umount debugfs]
>                           perf report #2 tries to open /debug file: kaboom
>                           perf report #2 exit
> 

Sorry, i not notice it, it can't work under this case.

> But your idea is sound if we only do the first half: we should mount it under 
> /sys/kernel/debug/ if it's not mounted already [and that directory is 
> available], and leave it mounted there.
> 

Um, i'll rewrite it and just mount it under /sys/kernel/debug

Thanks,
Xiao
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