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Date: Mon, 28 Apr 2008 22:35:35 +0300
From: Pekka Paalanen <pq@iki.fi>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Ingo Molnar <mingo@elte.hu>, Greg Kroah-Hartman <gregkh@suse.de>,
       linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: ftrace and debugfs weird interaction
Message-ID: <20080428223535.4fe2aeca@daedalus.pq.iki.fi>
In-Reply-To: <20080428153956.GH18776@elte.hu>
References: <20080426185403.GA22522@Krystal>
	<20080428153956.GH18776@elte.hu>
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> * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
> 
> > Hi,
> > 
> > When trying to figure out what was going on with the sched tracer
> > "tracing_enabled" file (sched-devel.git tree), I fell on this strange
> > behavior :
> > 
> > echo 1>tracing_enabled seems _not_ to send 1 to the tracing_ctrl_write

Wait a minute, are you literally running the command:
echo 1>tracing_enabled

If you are, you just echoed only a newline and directed stdout, stream 1,
to the file. No? :-)

Could you try with a space:
echo 1 > tracing_enabled

> > callback. However, sending garbage, e.g. echo s> tracing_enabled,
> > correctly sends the 's' character down the chain. echo 0>tracing_enabled
> > sometimes results in the callback not even being called.

Stream 0 is stdin, so... not sure what this would do. Probably nothing,
just like you experienced.


Thanks.

-- 
Pekka Paalanen
http://www.iki.fi/pq/