linux-kernel - Re: TRACE_EVENT

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Date:	Mon, 21 Sep 2009 19:58:53 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: TRACE_EVENT_ABI ?

On Mon, Sep 21, 2009 at 12:46:07PM -0400, Steven Rostedt wrote:
> On Mon, 2009-09-21 at 15:28 +0200, Arjan van de Ven wrote:
> > On Mon, 21 Sep 2009 09:26:41 -0400 (EDT)
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > > 
> > > [ Resending due to wrong SMTP server ]
> > > 
> > > 
> > > On Mon, 21 Sep 2009, Arjan van de Ven wrote:
> > > 
> > > > Hi,
> > > > 
> > > > Ingo suggested to make a TRACE_EVENT_ABI, which is equivalent in
> > > > implementation to TRACE_EVENT, except that it signals a stable
> > > > interface.
> > > > 
> > > > In trying to implement this I'm running into a wall where
> > > > TRACE_EVENT keeps being defined in many different ways all over the
> > > > place, making this a really nasty hack to make it just an alias.
> > > > 
> > > > Do you have any clever ideas on how to make this an alias without
> > > > fouling up the whole tracing system?
> > > > 
> > > 
> > > I don't know what you've done so far, but can't you simply in
> > > tracepoint.h define:
> > > 
> > > #define TRACE_EVENT_API(a,b,c,d,e) TRACE_EVENT(a,b,c,d,e)
> > 
> > unfortunately, due to the preprocessor trickery around TRACE_EVENT this
> > completely barfs.
> 
> I forgot to tell you about PARAMS.
> 
> This patch compiled for me;



Oh! PARAMS!

I've needed something to "contain" cpp args by the past so that they
are not substituted too early, which is needed while relaying cpp args
from a macro to another. I needed this to fix TRACE_EVENT_FN: it barfed
for the exact same reason.

So I've created __cpparg(), which I'm just discovering, does the exact
same thing than PARAM... :-/

I'm going to s/__cpparg/PARAM for the consistency.


 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 63a3f7a..9a983d6 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -280,6 +280,10 @@ static inline void tracepoint_synchronize_unregister(void)
>   * TRACE_EVENT_FN to perform any (un)registration work.
>   */
>  
> +#define TRACE_EVENT_API(name, proto, args, tstruct, assign, print)	\
> +	TRACE_EVENT(name, PARAMS(proto), PARAMS(args),			\
> +		    PARAMS(tstruct), PARAMS(assign), PARAMS(print))
> +
>  #define TRACE_EVENT(name, proto, args, struct, assign, print)	\
>  	DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
>  #define TRACE_EVENT_FN(name, proto, args, struct,		\
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index b48f1ad..0ee1eb6 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -149,7 +149,7 @@ TRACE_EVENT(sched_wakeup_new,
>   * (NOTE: the 'rq' argument is not used by generic trace events,
>   *        but used by the latency tracer plugin. )
>   */
> -TRACE_EVENT(sched_switch,
> +TRACE_EVENT_API(sched_switch,
>  
>  	TP_PROTO(struct rq *rq, struct task_struct *prev,
>  		 struct task_struct *next),
> 
> 

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