[Bf-committers] extension clause

Alex Combas blenderwell at gmail.com
Tue Nov 16 08:14:42 CET 2010

Taken from the GNU GPL FAQ:

"What legal issues come up if I use GPL-incompatible libraries with GPL

Answer (in part):

Both versions of the GPL have an exception to their copyleft, commonly
called the system library exception. If the GPL-incompatible libraries you
want to use meet the criteria for a system library, then you don't have to
do anything special to use them; the requirement to distribute source code
for the whole program does not include those libraries, even if you
distribute a linked executable containing them.

If you want your program to link against a library not covered by the system
library exception, you need to provide permission to do that. Below are two
example license notices that you can use to do that; one for GPLv3, and the
other for GPLv2. In either case, you should put this text in each file to
which you are granting this permission.

Only the copyright holders for the program can legally release their
software under these terms. If you wrote the whole program yourself, then
assuming your employer or school does not claim the copyright, you are the
copyright holder—so you can authorize the exception. But if you want to use
parts of other GPL-covered programs by other authors in your code, you
cannot authorize the exception for them. You have to get the approval of the
copyright holders of those programs.


So, all GPL licensed software already comes with an exception regarding the
use of non-GPL system libraries.

In addition to this, if the copyright holder provides permission to do so
then even GPL software is free to use
non-GPL *non-system* libraries.

If Blender became free to use non-GPL *non-system* libraries, then people
could write proprietary library extensions
which could be hooked into blender. The non-GPL libraries would require some
kind of interface, and that interface
would still be required to be GPL licensed software.

Does this sound like a reasonable compromise?

Is my understanding of this correct?

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