linux-kernel - Re: trace/events: DECLARE vs DEFINE semantic

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Message-Id: <1259813228.12870.108.camel@gandalf.stny.rr.com>
Date:	Wed, 02 Dec 2009 23:07:08 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	randy.dunlap@...cle.com, wcohen@...hat.com, fweisbec@...il.com,
	tglx@...utronix.de, jbaron@...hat.com,
	linux-tip-commits@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: trace/events: DECLARE vs DEFINE semantic

On Wed, 2009-12-02 at 23:00 -0500, Masami Hiramatsu wrote:
> Mathieu Desnoyers wrote:
> > In addition, I wonder if we should rename "CREATE_TRACE_POINTS" to
> > something more suitable while we are here ? Basically, it will affect
> > all TRACE_CLASS/TRACE_CLASS_EVENT/TRACE_EVENT from headers included
> > after it's defined.
> 
> Agreed, CREATE_TRACE_POINTS is a bit irritating thing :-(

Well, I think the name could use some help, but I don't think it is the
name that irritates you.

> 
> For example, if we call tracepoints defined in same-header on
> several different files, we need to check other people have
> already defined CREATE_TRACE_POINTS on another file, because
> CREATE_TRACE_POINTS must be used once for each header...
> 
> So, how about introducing a c file which is only for defining
> tracepoints for kernel parts ? or defining tracepoints in
> kernel at the beginning of kernel/tracepoint.c ? (and don't
> touch tracepoints in modules)

I think the proper fix is to have each tracepoint header have its own C
file. I believe Christoph does this with xfs.

Basically, we should have a:

kernel/sched_trace.c that includes the include/trace/events/sched.h and
does the define.

And the same goes for other trace points.

> 
> e.g.
> 
> @kernel/tracepoint.c
>  ...
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/sched.h>
>  #include <trace/events/...>

We could do this for all that is defined in the include/trace/events.

>  ...
> 
> @kernel/sched.c
>  ...
>  #include <trace/events/sched.h>	/* Just include events header */
>  ...
> 
> @fs/ext4/super.c (no change, since it can be module)
>  ...
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/ext4.h>

Perhaps we should move out anything in include/trace/events that is also
a module into its sub system?

>  ...
> 
> Hmm?

Hrmmm?

-- Steve


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