linux-kernel - Re: [PATCH 3/7] add syscall tracepoints

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Date:	Mon, 15 Jun 2009 10:12:10 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...e.hu,
	laijs@...fujitsu.com, rostedt@...dmis.org, peterz@...radead.org,
	jiayingz@...gle.com, bligh@...gle.com, roland@...hat.com,
	fche@...hat.com
Subject: Re: [PATCH 3/7] add syscall tracepoints

On Fri, Jun 12, 2009 at 05:57:26PM -0400, Mathieu Desnoyers wrote:
> > Introduce a new 'DECLARE_TRACE_REG()' macro, so that tracepoints can associate
> > an external register/unregister function.
> > 
> > 
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > 
> > ---
> >  include/linux/tracepoint.h |   27 +++++++++++++++++++++++----
> >  1 files changed, 23 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index 14df7e6..9a3660b 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -61,7 +61,7 @@ struct tracepoint {
> >   * not add unwanted padding between the beginning of the section and the
> >   * structure. Force alignment to the same alignment as the section start.
> >   */
> > -#define DECLARE_TRACE(name, proto, args)				\
> > +#define DECLARE_TRACE_REG(name, proto, args, reg, unreg)		\
> >  	extern struct tracepoint __tracepoint_##name;			\
> >  	static inline void trace_##name(proto)				\
> >  	{								\
> > @@ -71,13 +71,29 @@ struct tracepoint {
> >  	}								\
> >  	static inline int register_trace_##name(void (*probe)(proto))	\
> >  	{								\
> > -		return tracepoint_probe_register(#name, (void *)probe);	\
> > +		int ret;						\
> > +		void (*func)(void) = (void (*)(void))reg;		\
> > +									\
> > +		ret = tracepoint_probe_register(#name, (void *)probe);	\
> > +		if (func && !ret)					\
> > +			func();						\
> 
> I don't see why you need to add this weird interface when all you really
> need to do is to call the function to set the TIF flags explicitly in
> reg_event_syscall_enter when registering a tracepoint.
> 
> Mathieu
> 

I could enable the TIF flag in reg_event_syscall_enter, however that
would not manage the TIF flag for other users of these traceoints. When
users 'register/unregister' with a tracepoint, they expect the tracepoint
to be enabled/disabled. If we move this functionality to the user, we are
changing how that interface works. Therefore, I associated the
enabling/disabling of the tracepoint, with the tracepoint definition.

thanks,

-Jason
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