Subject: Re: [PATCH 02/10][RFC] tracing: Let tracepoints have data passed
 to tracepoint callbacks
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Mathieu Desnoyers <compudj@krystal.dyndns.org>,
       Lai Jiangshan <laijs@cn.fujitsu.com>,
       Masami Hiramatsu <mhiramat@redhat.com>, Christoph Hellwig <hch@lst.de>,
       Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <4BD6A98D.6010706@cn.fujitsu.com>
References: <20100426195024.256424113@goodmis.org>
	 <20100426200241.631945432@goodmis.org>  <4BD6A98D.6010706@cn.fujitsu.com>
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Organization: Kihon Technologies Inc.
Date: Tue, 27 Apr 2010 11:28:26 -0400
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On Tue, 2010-04-27 at 17:08 +0800, Li Zefan wrote:
> Steven Rostedt wrote:

> > Because of the data parameter, tracepoints declared this way can not have
> > no args. That is:
> > 
> >   DECLARE_TRACE_DATA(mytracepoint, TP_PROTO(void), TP_ARGS());
> > 
> > will cause an error, but the original DECLARE_TRACE still allows for this.
> > 
> > The DECLARE_TRACE_DATA() will be used by TRACE_EVENT() so that it
> > can reuse code and bring the size of the tracepoint footprint down.
> > This means that TRACE_EVENT()s must have at least one argument defined.
> 
> We have to define at least on argument in TRACE_EVENT() even without
> this patch, otherwise it'll cause compile error while expanding the
> macros.

OK, good to know that this is not a regression. The DECLARE_TRACE()
still allows now arguments, I spent a bit of time (more than I wanted
to) to make that work. Since I added a new DECLARE_TRACE_DATA() that
must have at least one argument, it is not a regression, because it is
new :-)

Thanks,

-- Steve

P.S.

I'll let these patches sit out for a week waiting for comments, and if
there are none, I'll repackage them (rebase as well) and send them out
for real.


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