[quagga-dev 11484] Re: non-GPL code calling and depending on GPL libzebra

Jeroen Massar jeroen at massar.ch
Thu Sep 11 11:09:05 BST 2014

On 2014-09-11 08:56, Paul Jakma wrote:
> Hi,
> My understanding of software copyright and GPL licensing is that when
> you have code A that has a specific dependency on code B, then the
> author of code B has a copyright claim over code A.

No, you are using the wrong words in the wrong places :)

The person/entity that writes the code automatically has the copyright.
Normally one states that by adding a "(c)<year> <name>" though in most
legalities one does not even have to do that.

Copyright does not get transfered automatically because of a viral
license like the GPL.

Copyright only gets transfered when the author explicitly assigns
copyright to another entity.

What does happen is when you *link* code A to GPL-code B, then you are
required by the GPL to also release A under the GPL.

> E.g., if code A calls, uses and depends on Quagga's libzebra[1], then
> code A must conform with the GPL licence of libzebra where copyright
> applies (e.g. copying code A, in source or binary form, outside of
> exceptions provided by copyright law).

Writing it that way is mostly correct. But not it is not copyright

> If code A is distributed under, e.g., a BSD licence, then this would not
> conform with the GPL licence applicable to it, as the BSD licence is not
> compatible with the GPL in this way[2].

Hence why the LGPL exists. That is what one should use for libraries,
like libzebra.

> That is my understanding of things. I havn't had reason till now to
> think it was wildly off the mark. It'd be useful to hear of very
> concrete legal opinion to the contrary.
> Next, I'm curious what issues could arise if Quagga started distributing
> a daemon under a BSD licence, with that daemon calling libzebra

As you own the copyright on both parts, you can do whatever you want.
Dual-licensing, commercial selling. Your thing.

Though, as there are multiple contributors, you might need to verify
with them that they assigned the copyright of the code they submitted to
a Quagga entity that can make those decisions... (hence why there are
projects which require that, and eg why GNU does that).

Btw, instead of a BSD license, think of Apache License 2.0 it has a few
nice protections for patenty loopholes.


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