confused about Qt QPL/GPL license

(EDIT: changed the title. Thanks for the discussion, I am less confused now :) )

How many of you, when confronted with the Qt licensing option (during the 'configure' step of the compile) select the GPL as your Qt/X11 license? I had always done so, but I have come to understand that using KDE precludes this option.

If you use KDE, the QPL is your only non-commercial licensing option, because a GPL'd library cannot be linked with non-GPL code. KDE contains lots of this. Here's a partial list, just of the core apps and libs:

  • kdelibs (LGPL)
  • kwin (BSD)
  • kicker (BSD)
  • ksmserver (BSD)
  • klipper (Artistic)

There are many more besides these.

Anyway, just some food for thought. Since there's no *explicit* choice made between QPL and GPL, I guess anyone who mistakenly chose the GPL like I did can just retroactively change their mind and continue using Qt under the QPL. I have heard the opinion that the Qt licensing option can be interpeted as allowing the user to decide on a per-application basis which license they will use, but I can't really buy that. Besides, it doesn't matter since kdelibs is LGPL'd, and therefore can't be linked with GPL'd Qt/X11. (EDIT: actually, combining a GPL'd lib with a LGPL'd lib can be allowed, *if* the resulting app is GPL'd. So maybe there's hope for this "per-application" Qt licensing meme, though it still seems like a huge stretch to me)

BTW, why not eliminate the GPL option in qt-copy? It just adds confusion.

(EDIT: how am I supposed to insert paragraph breaks? it doesn't recognize the p tag, so I used two br's in a row)


You're more than allowed to link GPL against non-GPL code. As long as the non-GPL code is more liberally licensed.

By KDE User at Tue, 08/26/2003 - 20:13

Did you follow the link in my post? I'll save you a click:

Q: If a library is released under the GPL (not the LGPL), does that mean that any program which uses it has to be under the GPL?

A: Yes, because the program as it is actually run includes the library.

So what part of that makes me "wrong, wrong, wrong"?

(EDIT: I think you may be thinking of the situation where you have a "more liberally licensed" *library* linked against a GPL'd *application*, which I agree is more than allowed. However, the reverse situation (GPL'd library linked in a non-GPL'd app) is *not* allowed by the GPL)

KStars: A desktop planetarium for KDE

By Jason Harris at Tue, 08/26/2003 - 20:36

The part that makes you think that makes it impossible for us to use more liberal licenses in KDEs code. The code can be BSD, Artistic. LGPL or whatever, it is only the linked program that has to become GPL unless someone has paid Trolltech.

So you are dead wrong. Sorry.

By KDE User at Tue, 08/26/2003 - 20:51

I don't understand what you are saying. Nowhere did I say or mean to imply that KDE code could not be licensed under BSD or Artistic or whatever other OSS license. I only said that doing so demands that the QPL is used when licensing Qt.

KStars: A desktop planetarium for KDE

By Jason Harris at Tue, 08/26/2003 - 20:54

You can perfectly well link BSDd code to GPLd code. All the GPL
restriction means is that if the user of the BSD code doesn't
have any additional rights to the GPLd code, he can't use the additional
right offered by the BSD license. But if the user has some additional rights
to the code offered under the GPL (like original copyright or a
commercial license) he can use the BSDd code to a full extent.
i.e. TrollTech can easily incorproprate any BSDd code using Qt into
one of their products. (While theu can't do that w/the GPLd code)

By KDE User at Tue, 08/26/2003 - 21:46

I don't know what to say, except to ask you to please read the FAQ entry that I both linked to and posted directly. It isn't ambiguous, and it conflicts with what you are claiming. It says: "code linked with a GPL'd library must be GPL'd", does it not?

KStars: A desktop planetarium for KDE

By Jason Harris at Tue, 08/26/2003 - 21:58

Nevermind, I understand now that the license for the binary version of an application is not necessarily the same as the license for the application's source code (i.e., while the linked binary must be GPL'd the application source code can be "merely" GPL-compatible). Sorry for my confusion.

KStars: A desktop planetarium for KDE

By Jason Harris at Tue, 08/26/2003 - 23:20

first, paragraph breaks: just hit enter a couple times. it automatically turns them into paragraphs for you ...

second, you're wrong about the licensing issue. it doesn't ask you to choose one or ther other, it asks you to agree to it being licensed for use under either the QPL or the GPL. when you say "yes" you are agreeing to the dual license, not one or the other. re-read the question that configure asks a bit better.

By Aaron J. Seigo at Tue, 08/26/2003 - 20:16

Like I said, I was mistaken when I thought I was able to license Qt under the GPL as a KDE user. The "dual licensing" seems like an unnecessary complication. The only license that lets you use KDE is the QPL, so why bother with this dual-licensing fuzziness? Wouldn't it be simpler (and more accurate) to just say we're using Qt licensed with the QPL?

KStars: A desktop planetarium for KDE

By Jason Harris at Tue, 08/26/2003 - 20:46

it seems you perceive it as an either/or situation between the GPL and the QPL, but it isn't. it's a "both" situation. you aren't choosing one license versus another, you are running Qt under BOTH licenses at the same time.

the QPL is not compatible with all licenses in KDE, for instance the GPL (AFAIK, anyways). but the GPL is compatible with the GPL (of course ;). so when you license Qt under a dual QPL/GPL license, you can run it with every bit of code in KDE's CVS.

does that help make it any clearer?

By Aaron J. Seigo at Tue, 08/26/2003 - 21:05