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

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Date:	Fri, 19 Jun 2009 05:40:53 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, peterz@...radead.org,
	mathieu.desnoyers@...ymtl.ca, jiayingz@...gle.com,
	bligh@...gle.com, roland@...hat.com, fche@...hat.com
Subject: Re: [PATCH 3/7] add syscall tracepoints

On Thu, Jun 18, 2009 at 11:29:29PM -0400, Steven Rostedt wrote:
> 
> On Fri, 19 Jun 2009, Frederic Weisbecker wrote:
> 
> > On Fri, Jun 12, 2009 at 05:24:49PM -0400, Jason Baron 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)		\
> > 
> > 
> > 
> > May be it deserves a comment? DECLARE_TRACE_REG() as a name is not enough
> > obvious on its own :)
> 
> I agree. I was talking with Christoph Hellwig about doing something 
> similar with TRACE_EVENT, since he needs to do special things when enabled 
> and disabled (like enable other trace points).
> 
> But anyway, I totally NAK the name. What about something like 
> DECLARE_TRACE_WITH_CALLBACK()
> 
> Yes, it is a bit more verbose, but it at least tells what it does.


Yeah, sounds good.



> The first thing that came to my mind when I saw DECLARE_TRACE_REG, was that 
> this trace point will pass in "regs" to do things like backtraces.


Ah, the first thing that came to me was a tracepoint that did something
weird with a mysterious registry...and then my imagination got stucked
there.


Frederic.

 
> -- Steve
> 
> > 
> > 
> > 
> > >  	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();						\
> > > +		return ret;						\
> > >  	}								\
> > >  	static inline int unregister_trace_##name(void (*probe)(proto))	\
> > >  	{								\
> > > -		return tracepoint_probe_unregister(#name, (void *)probe);\
> > > +		int ret;						\
> > > +		void (*func)(void) = (void (*)(void))unreg;		\
> > > +									\
> > > +		ret = tracepoint_probe_unregister(#name, (void *)probe);\
> > > +		if (func && !ret)					\
> > > +			func();						\
> > > +		return ret;						\
> > >  	}
> > >  
> > > +
> > > +#define DECLARE_TRACE(name, proto, args)		\
> > > +	DECLARE_TRACE_REG(name, TP_PROTO(proto), TP_ARGS(args), 0, 0);
> > > +
> > >  #define DEFINE_TRACE(name)						\
> > >  	static const char __tpstrtab_##name[]				\
> > >  	__attribute__((section("__tracepoints_strings"))) = #name;	\
> > > @@ -94,7 +110,7 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
> > >  	struct tracepoint *end);
> > >  
> > >  #else /* !CONFIG_TRACEPOINTS */
> > > -#define DECLARE_TRACE(name, proto, args)				\
> > > +#define DECLARE_TRACE_REG(name, proto, args, reg, unreg)		\
> > >  	static inline void _do_trace_##name(struct tracepoint *tp, proto) \
> > >  	{ }								\
> > >  	static inline void trace_##name(proto)				\
> > > @@ -108,6 +124,9 @@ extern void tracepoint_update_probe_range(struct tracepoint *begin,
> > >  		return -ENOSYS;						\
> > >  	}
> > >  
> > > +#define DECLARE_TRACE(name, proto, args)                \
> > > +	DECLARE_TRACE_REG(name, TP_PROTO(proto), TP_ARGS(args), 0, 0);
> > > +
> > >  #define DEFINE_TRACE(name)
> > >  #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
> > >  #define EXPORT_TRACEPOINT_SYMBOL(name)
> > > -- 
> > > 1.6.0.6
> > > 
> > 
> > 

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