linux-kernel - Re: ftrace and debugfs weird interaction

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Message-ID: <20080428153956.GH18776@elte.hu>
Date:	Mon, 28 Apr 2008 17:39:56 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Pekka Paalanen <pq@....fi>
Subject: Re: ftrace and debugfs weird interaction


* Mathieu Desnoyers <mathieu.desnoyers@...ymtl.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
> 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.
> 
> The debugfs file has been created with
> 
>         entry = debugfs_create_file("tracing_enabled", 0644, d_tracer,
>                                     &global_trace, &tracing_ctrl_fops);
>         if (!entry)
>                 pr_warning("Could not create debugfs 'tracing_enabled' entry\n");
> 
> I wonder what kind of weird debugfs interaction we might have here ?

hm. Cc:-ed more ftrace developers.

	Ingo
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