linux-kernel - Re: Dual-licensing LTTng, marker and tracepoints under GPLv2+/LGPLv2.1+

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Date:	Wed, 24 Jun 2009 12:49:09 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Christoph Hellwig <hch@...radead.org>,
	Pierre-Marc Fournier <pierre-marc.fournier@...ymtl.ca>,
	Tom Zanussi <tzanussi@...il.com>, karim@...rsys.com,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	ltt-dev@...ts.casi.polymtl.ca,
	Lai Jiangshan <laijs@...fujitsu.com>,
	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Robert Wisniewski <bob@...son.ibm.com>
Subject: Re: Dual-licensing LTTng, marker and tracepoints under
	GPLv2+/LGPLv2.1+

* Frank Ch. Eigler (fche@...hat.com) wrote:
> Mathieu Desnoyers <compudj@...stal.dyndns.org> writes:
> 
> > [...]  The goal we pursue by dual-licensing with GPLv2/LGPLv2.1 is
> > to permit instrumented applications to be themselves distributed
> > under other license than GPL. [...]
> 
> Is there some reason you can't just fork/copy off some earlier version
> of these files over which you had sole authorship (if any)?
> 

Actually, for LTTng, I own the copyright of almost everything we need.
Most files written by others are mainly the debugfs interfaces done by
Fujitsu. There is some derived work from RelayFS in
ltt/ltt-relay-alloc.c and include/linux/ltt-relay.h, where getting IBM's
approval would be good, but I think in the end this will end up being
only a few tens of lines.

> 
> > [...]The goal is to permit this library, which includes the
> > tracepoints, markers and LTTng features, to be used by userspace
> > applications and libraries so they can add static instrumentation
> > (as we currently do in the kernel). [...]
> 
> Just in case you're not aware, some API prior art for this is the
> dtrace sdt.h widget (already supported by systemtap), and of course
> it has no similarity to the various kernel tracing APIs.

Yep, we're aware of this. However, last time I checked, dtrace SDT used
a breakpoint even for their userspace tracing, which has a way too large
performance overhead for our needs.

Moreover, they support only very, very limited typing (0 to 5 u32). In
this respect, tracepoints and markers are much more flexible.

Thanks,

Mathieu

> 
> - FChE
> 

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