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

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Date:	Thu, 03 Dec 2009 08:51:22 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
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

Steven Rostedt wrote:
> 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.

Yes :-)

>> 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.

Hmm, I'd rather like to move it into kernel/events/ or something new
sub directory, since those files will have just two lines (define and
include).

>> 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?

Would you mean putting those headers in sub-system's directory?
(e.g. fs/ext4/)
In that case, a problem will happen when user want to hook those
tracepoint from their module, because it is hard to find those
local headers.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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