Can I release an extension to a GPL'd library under a BSD-esque license?

Question

Consider a Java library "A", which is available under GPL v2, and under a proprietary commercial license.

My company has licensed library A under its commercial license, and I've developed an extension to it, which we'd like to release (to github or whatever). However, we want the extension to be usable by all users of library A, including those who have licensed it commercially, so releasing the extension under GPL is undesirable.

Note that this extension requires library A at compile-time and runtime.

Is it enough to simply provide the sources of the extension under a BSD-esque license, and state that any users of it must acquire library A independently (either under the GPL or via the commercial license made available by the library's publisher)?

Or, is it the case that, because my extension requires a GPL'd library, it must be licensed under the GPL as well?

IANAL (obviously!), and I've already spent about a half hour reading the GPL FAQ (which only confused me more with its discussion of aggregate/derivative works, linking vs. fork/exec, distribution and dependencies, etc). Any clear guidance is most welcome, in my first foray into GPL-related licensing issues.

Answer 1

If your code includes any part of the software licensed under GPL you won't be able to to release it under BSD. If you are giving away something that users of library A can use, but that people who don't have library A can't use AND it doesn't include any part of library A, you can release it under BSD.

Answer 2

Well, IANAL obviously, but while the GPL requires derived works to be licensed under the GPL as well, there is no requirement that it cannot be licensed under other licenses additionally.

So I believe you should dual-license (GPL + BSD). Then users of your library can choose either the GPL (if they use A under GPL), or BSD (if they have a proprietary license for A).

Answer 3

Why not submit the extensions back to the original library maintainers and ask them to incorporate them in the original library? That way, they have worry about the licensing, not you.

Answer 4

As long as you don't distribute a binary that is linked to the library it should be perfectly ok to share your code under a license of your own liking and tell people to get either the GPL or the commercial version of the lib to compile and run your code.

Of course you need te make sure that your license is compatible to both the commercial license and to the GPL, otherwise people will not be able to use it.

Answer 5

Why not (a) GPL+commercial dual license, or (b) LGPL?

LGPL is similar to, and compatible with, GPL, but also allows commercial use.