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

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Message-ID: <20091203144221.GA28823@Krystal>
Date:	Thu, 3 Dec 2009 09:42:21 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>, 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 (rostedt@...dmis.org) wrote:
> On Thu, 2009-12-03 at 09:09 -0500, Mathieu Desnoyers wrote:
[...]
> > Maybe we could have separate files for:
> > 
> > a) event definitions
> > b) class definitions
> 
> Um, because we don't add classes nor definitions for that matter in C
> files. These files will just have:
> 
> #define CREATE_TRACE_POINT
> #include <trace/event/x.h>
> #include <trace/event/y.h>
> [...]
> 
>
[...] 
> > I agree with Steven here: modules should come with their own trace event
> > definitions, and if the trace classes they use are not available in the
> > standard kernel, they should come with these trace classes definitions
> > too.
> > 
> > A small *_trace.c file linked along with the module looks fine by me.
> > 
> > And please, try to re-used the already existing symbol dependency
> > management already present in the kernel to deal with module dependency
> > on class and dependency such as:
> > 
> >   module-a.ko
> >     defines trace class
> >   module-b.ko
> >   module-c.ko
> > 
> >     module-b and module-c define events which depend on the trace class.
> > 
> > If you make the event definition depend on a symbol defined in module-a,
> > everything should work flawlessly. It also works if the class is defined
> > in the core kernel.
> 
> I think the issue is where to find the headers.
> 
> But this does bring up another point. I don't think I designed the class
> macro to be used by events in other headers. Looking at the code, since
> all the shared functions are "static" it wont work.
> 
> I guess I can modify it to be global, and also export them as GPL.

In that case maybe it would become appropriate to extract the
TRACE_CLASS() macros meant to be used by many headers into their own

include/trace/class/*.h

headers ?

And then it starts to make sense to have separate C files for event and
class definitions.

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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