dbus: Proposed relicense to MIT/X11

[Ryan Lortie]

On Thu, 2007-20-09 at 10:44 +0200, Michael Albinus wrote:
> I'm currently writing a D-BUS integration into GNU Emacs. Sounds to me
> like I can stop the project, GNU Emacs is GPLv3 licensed. I do not
> plan to make any fork of dbus code.

I believe that you are misunderstanding the GPL.

The same thing that makes a GPL-only fork of dbus possible makes linking
possible.  Namely: the MIT/X11 license is, in no way, more restrictive
than the GPL.  Under the MIT/X11 license you have every right that you
also have under the GPL.

As such, any code available under the terms of the MIT/X11 license is
also automatically _effectively_ available under the terms of the GPL:
you're allowed to do anything with it that the GPL would allow you to
do.

You could argue that the "no warranty" and "you must preserve these
copyright notices" parts of the MIT/X11 license are additional
restrictions and therefore you don't have your full GPL rights, but see
GPLv3 §7, "Additional Terms":

    Notwithstanding any other provision of this License, for material
    you add to a covered work, you may (if authorized by the copyright
    holders of that material) supplement the terms of this License with
    terms:

    a) Disclaiming warranty or limiting liability differently from the
       terms of sections 15 and 16 of this License; or

    b) Requiring preservation of specified reasonable legal notices or
       author attributions in that material or in the Appropriate Legal
       Notices displayed by works containing it; or

    (among other permitted terms)

This means that you can add MIT/X11 code to your work, either by copying
code from it or linking against it.  The GPLv3 includes this section
specifically to permit this sort of compatibility with other licenses.

You don't have to take my word for it either :).  See the FSF's own
interpretation at http://www.gnu.org/philosophy/license-list.html:

    X11 License

    This is a simple, permissive non-copyleft free software license,
    compatible with the GNU GPL. Older versions of XFree86 used the same
    license, and some of the current variants of XFree86 also do. Later
    versions of XFree86 are distributed under the XFree86 1.1 license.

    This license is sometimes called the MIT license, but that term is
    misleading, since MIT has used many licenses for software.

Hope this clears up any problems :)

Cheers