linux-kernel - Re: [PATCH 02/10][RFC] tracing: Let tracepoints have data passed to tracepoint callbacks

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Date:	Tue, 27 Apr 2010 11:28:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH 02/10][RFC] tracing: Let tracepoints have data passed
 to tracepoint callbacks

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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