linux-kernel - Re: ftrace and debugfs weird interaction

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Message-ID: <Pine.LNX.4.58.0804281523260.4615@gandalf.stny.rr.com>
Date:	Mon, 28 Apr 2008 15:27:21 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, Pekka Paalanen <pq@....fi>
Subject: Re: ftrace and debugfs weird interaction

5BOn Mon, 28 Apr 2008, Ingo Molnar wrote:

>
> * 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

It should actually send "1" and not 1 (and technically "1\n") ;-)

> > 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.

I haven't seen this. Perhaps I'm confused about what you are seeing.

> >
> > 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 ?

This looks normal to me. Could you provide a bit more detail to what you
are doing, what the results are, and what you expect the restults to be?

>
> hm. Cc:-ed more ftrace developers.

Thanks,

-- Steve
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