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Re: LGPL-library (tntdb) linked with GPL-library (mysql)



On Sat, 26 Aug 2006 14:18:00 +0300 Markus Laire wrote:

> On 8/26/06, Don Armstrong <don@debian.org> wrote:
> > On Sat, 26 Aug 2006, Markus Laire wrote:
[...]
> > > Because according to your interpretation I would be able to use
> > > *any* GPL:ed library using the terms of LGPL with this simple
> > > trick:
> >
> > You are misunderstanding my interpretation.
> >
> > > 1. Take a GPL:ed library
> > > 2. Create LGPL:ed library which uses the GPL:ed library, and
> > > offers the exact same functionality.
> > > 3. Use the created LGPL:ed library instead of the original one, to
> > > get exact same functionality without (some) restrictions of the
> > > GPL.
> >
> > This requires complying with the GPL because you are creating a
> > derivative work of the GPLed work.
> 
> But isn't this exactly what the original poster asked: Can you LGPL a
> program (tntdb) which links with GPL:ed program (mysql)?

No, the original poster asked if the *copyright holder* of a work
(tntdb), which links with a GPLed work (mysql), can change the license
of his own work (tntdb) to LGPL, and still create a distributable (by
other people) binary package!

Since he's the copyright holder, he can choose any license he likes, of
course.

The issue is: will the resulting binary package be distributable by
other people?
Assuming (to be on the safe side) that the FSF's legal theory on linking
is true: when you distribute tntdb in binary form linked against GPLed
mysql, you must make the source code for both available under the GPL.
Hence, the question rises: would an LGPLed tntdb be available under the
GPL?
And the answer is: yes, because of the explicit LGPL->GPL conversion
clause found in the LGPL (and quoted by Don Armstrong).  Any work under
the LGPL is effectively available under the GPL too (but the reverse is
not true!).

> 
> First you answered that it's OK to use LGPL for tntdb even if it links
> with mysql.

True: it's OK that the *copyright holder* of tntdb adopts the LGPL for
tntdb, even if it links with mysql, which is GPLed.
See above for the detailed explanation.

> Now you are saying the reverse, that it's not OK to use LGPL for tntdb
> if it links with mysql.

Not exactly: it's not possible for anyone (except the copyright holder)
to change the license of mysql from GPL to LGPL, because that conversion
is not allowed by the GPL.
In your example above you supposed to create an LGPLed wrapper library
for a GPLed library in order to escape the restrictions of the GPL.  And
that is not possible, because (again under the FSF's theory) the
combination LGPLed_library + GPLed_library would need to be entirely
under the GPL (thus triggering the LGPL->GPL conversion clause), and all
GPL restrictions would still be active.

> 
> > The LGPL is compatible with the GPL because it can become the GPL.
> > The reverse is not true, which is what your example is proposing.
> 
> IMHO, the original question was about the reverse, and so your answer
> was wrong.

No, I don't think that Don Armstrong's answer was wrong.  A bit
summarized, perhaps, but not wrong.

I hope I have somewhat clarified...  :p


-- 
But it is also tradition that times *must* and always
do change, my friend.   -- from _Coming to America_
..................................................... Francesco Poli .
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