linux-kernel - ftrace and debugfs weird interaction

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Date:	Sat, 26 Apr 2008 14:54:03 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Greg Kroah-Hartman <gregkh@...e.de>, Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: ftrace and debugfs weird interaction

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 ?

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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