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SubjectRe: ftrace and debugfs weird interaction
On Sat, Apr 26, 2008 at 02:54:03PM -0400, Mathieu Desnoyers 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 ?

I don't know. Are you sure your _fops is not getting called at all?

How about using a "default" operation for such a simple file, like
debugfs_create_bool() as that is all you care about for this kind of
value?

That should save you some code at the very least :)

thanks,

greg k-h


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