[quagga-dev 11480] non-GPL code calling and depending on GPL libzebra

Paul Jakma paul at jakma.org
Thu Sep 11 07:56:46 BST 2014


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. The author of code A must then 
conform to the conditions of any licence given by the author of code B for 
code B, so far as copyright law demands (aside: which is quite far, IMLU).

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).

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].

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. If my 
understanding above is correct, is this just a triviality that can be 
ignored? What are the consequences to Quagga? Are there consequences for 

Opinions, examples, etc., would be very much welcomed.



1. Not an exhaustive list of how code A might come to depend on libzebra. 
IANAL, etc.

2. My understanding is that distributing modern-BSD licensed code as GPL 
is permissible, as the GPL meets the requirements of the modern-BSD 
licence, where modern-BSD licence is without the advertising clause.

Paul Jakma	paul at jakma.org	@pjakma	Key ID: 64A2FF6A
You will be held hostage by a radical group.

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