From OpenSourceSoftwarePractice

Contents 1 Sub-Licensing / Re-Licensing 1.1 Background 1.2 Relevant links 1.3 Questions

Sub-Licensing / Re-Licensing

Background

This past week there's been a lot of controversy in the Linux and OpenBSD communities over a licensing change to some code that was shared between them. I've been following the issue and am steadily getting more confused on a number of points concerning the obligations of the BSD license and the nature of dual-licensing, re-licensing, and sub-licensing. I was wondering if this could be addressed in class, or if someone would be prepared to talk about it after class.

Relevant links

• http://undeadly.org/cgi?action=article&sid=20070829001634
• http://lkml.org/lkml/2007/8/28/157
• http://kerneltrap.org/OpenBSD/Stealing_Versus_Sharing_Code

Questions

1. What is the difference between re-licensing and sub-licensing? Without definitions I'm left to guess that re-licensing potentially replaces an existing license (a privilege only the copyright holder has), and that sub-licensing adds an additional license that is compatible with the existing one.
2. When a work is dual-licensed, is it required that modifications to the work be dual-licensed as well, or is the user free to pick one over another and essentially fork the code? My previous understanding was that the license grants you authority to redistribute verbatim and/or derivative works, therefore it is not necessary for the recipient to use more than one license of a multi-licensed work, and the others can be safely discarded. However, I'm now coming to suspect that when creating a derived work, one can choose which license to use from the original portion for compatibility with the whole result, but one may not change or further restrict the license on the original portion. If this is true, then a GPLv2/BSD dual-license seems redundant, as one would not normally be able to make a GPL-only fork except by virtue of the license of additional code by a non-copyright-holder.
3. Is the removal of the do-not-remove-me notice of a BSD licensed file ever legal (for a non-copyright-holder), and under what circumstances? When a derived work is created, for example by adding code to a source file, how does one keep the license of the whole file clear and unambiguous without modifying the original notice?
4. By default, can licenses be revoked at will by the copyright holder? The GPL has conditions under which the license is voided for a particular user; assuming those are not met, is the continued right to redistribute under the license guaranteed?