linux-kernel - Re: Relicensing tracepoints and markers to Dual LGPL v2.1/GPL v2,headers to Dual BSD/GPL

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Message-Id: <1256563793.26028.240.camel@gandalf.stny.rr.com>
Date:	Mon, 26 Oct 2009 09:29:52 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>
Cc:	Ingo Molnar <mingo@...e.hu>, GeunSik Lim <leemgs1@...il.com>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Jesper Juhl <jj@...osbits.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Adrian Bunk <bunk@...sta.de>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>,
	Jaswinder Singh Rajput <jaswinderrajput@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Dominique Toupin <dominique.toupin@...csson.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: Relicensing tracepoints and markers to Dual LGPL v2.1/GPL
 v2,headers to Dual BSD/GPL

On Mon, 2009-10-26 at 09:17 -0400, Pierre-Marc Fournier wrote:
> Ingo Molnar wrote:
> > 
> > But i also disagree with it on a technical level: code duplication is 
> > _bad_. Why does the code have to be duplicated in user-space like that? 
> > I'd like Linux tracing code to be in the kernel repo. Why isnt this done 
> > properly, as part of the kernel project - to make sure it all stays in 
> > sync?
> > 
> 
> If you mean that this code should solely be used inside the kernel, then
> what you propose technically does not work. There is a very high cost to
> accessing kernel code from userspace. This cost is simply unacceptable
> for the kind of userspace tracing that is needed today.

I think that Ingo is thinking that the tracing is for the kernel, and is
asking why the duplication needs to be done for tools tracing the
kernel.

But what I think is trying to be done here is to use the same types of
MACROS that we have in the kernel to do tracing in userspace. That a
userspace program can add their own "TRACE_EVENT" and that the headers
there will create a tracepoint for them the same way we currently do in
the kernel.

Am I correct in my analysis?

-- Steve


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