Re:GFDL in the kernel tree

From: Xose Vazquez Perez (
Date: Sun Jun 15 2003 - 09:38:29 EST


Christoph Hellwig wrote:

> And of course there's still all those nasty issue with GFDL like
> invariant sections and cover texts that make at least the debian-devel
> list believe it's an unfree license..
> Folks, could we please only use GPL-compatible licenses in the kernel
> tree?

speaking about licenses, Red Hat guys have included into the kernel a
new file, COPYING.modules, about modules license. It would be interesting
to have it into official kernels too.

more info about 'Proprietary kernel modules':


Software is like sex, it's better when it's bug free.

Date: Thu, 17 Oct 2002 10:08:19 -0700 (PDT) From: Linus Torvalds <> To: Christoph Hellwig Cc: <> Subject: Re: [PATCH] make LSM register functions GPLonly exports In-Reply-To: <> Message-ID: <>

Note that if this fight ends up being a major issue, I'm just going to remove LSM and let the security vendors do their own thing. So far

- I have not seen a lot of actual usage of the hooks - seen a number of people who still worry that the hooks degrade performance in critical areas - the worry that people use it for non-GPL'd modules is apparently real, considering Crispin's reply.

I will re-iterate my stance on the GPL and kernel modules:

There is NOTHING in the kernel license that allows modules to be non-GPL'd.

The _only_ thing that allows for non-GPL modules is copyright law, and in particular the "derived work" issue. A vendor who distributes non-GPL modules is _not_ protected by the module interface per se, and should feel very confident that they can show in a court of law that the code is not derived.

The module interface has NEVER been documented or meant to be a GPL barrier. The COPYING clearly states that the system call layer is such a barrier, so if you do your work in user land you're not in any way beholden to the GPL. The module interfaces are not system calls: there are system calls used to _install_ them, but the actual interfaces are not.

The original binary-only modules were for things that were pre-existing works of code, ie drivers and filesystems ported from other operating systems, which thus could clearly be argued to not be derived works, and the original limited export table also acted somewhat as a barrier to show a level of distance.

In short, Crispin: I'm going to apply the patch, and if you as a copyright holder of that file disagree, I will simply remove all of he LSM code from the kernel. I think it's very clear that a LSM module is a derived work, and thus copyright law and the GPL are not in any way unclear about it.

If people think they can avoid the GPL by using function pointers, they are WRONG. And they have always been wrong.


------------------------------------------------------------------------ Date: Fri, 19 Oct 2001 13:16:45 -0700 (PDT) From: Linus Torvalds <> To: Barnes Subject: Re: GPL, Richard Stallman, and the Linux kernel

[ This is not, of course, a legal document, but if you want to forward it to anybody else, feel free to do so. And if you want to argue legal points with me or point somehting out, I'm always interested. To a point ;-]

On Fri, 19 Oct 2001, Barnes wrote: > > I've been exchanging e-mail with Richard Stallman for a couple of > weeks about the finer points of the GPL.

I feel your pain.

> I've have spent time pouring through mailing list archives, usenet, > and web search engines to find out what's already been covered about > your statement of allowing dynamically loaded kernel modules with > proprietary code to co-exist with the Linux kernel. So far I've > been unable to find anything beyond vague statements attributed to > you. If these issues are addressed somewhere already, please refer > me.

Well, it really boils down to the equivalent of "_all_ derived modules have to be GPL'd". An external module doesn't really change the GPL in that respect.

There are (mainly historical) examples of UNIX device drivers and some UNIX filesystems that were pre-existing pieces of work, and which had fairly well-defined and clear interfaces and that I personally could not really consider any kind of "derived work" at all, and that were thus acceptable. The clearest example of this is probably the AFS (the Andrew Filesystem), but there have been various device drivers ported from SCO too.

> Issue #1 > ======== > Currently the GPL version 2 license is the only license covering the > Linux kernel. I cannot find any alternative license explaining the > loadable kernel module exception which makes your position difficult > to legally analyze. > > There is a note at the top of, > but that states "user programs" which would clearly not apply to > kernel modules. > > Could you clarify in writing what the exception precisely states?

Well, there really is no exception. However, copyright law obviously hinges on the definition of "derived work", and as such anything can always be argued on that point.

I personally consider anything a "derived work" that needs special hooks in the kernel to function with Linux (ie it is _not_ acceptable to make a small piece of GPL-code as a hook for the larger piece), as that obviously implies that the bigger module needs "help" from the main kernel.

Similarly, I consider anything that has intimate knowledge about kernel internals to be a derived work.

What is left in the gray area tends to be clearly separate modules: code that had a life outside Linux from the beginning, and that do something self-containted that doesn't really have any impact on the rest of the kernel. A device driver that was originally written for something else, and that doesn't need any but the standard UNIX read/write kind of interfaces, for example.

> Issue #2 > ======== > I've found statements attributed to you that you think only 10% of > the code in the current kernel was written by you. By not being the > sole copyright holder of the Linux kernel, a stated exception to > the GPL seems invalid unless all kernel copyright holders agreed on > this exception. How does the exception cover GPL'd kernel code not > written by you? Has everyone contributing to the kernel forfeited > their copyright to you or agreed with the exception?

Well, see above about the lack of exception, and about the fundamental gray area in _any_ copyright issue. The "derived work" issue is obviously a gray area, and I know lawyers don't like them. Crazy people (even judges) have, as we know, claimed that even obvious spoofs of a work that contain nothing of the original work itself, can be ruled to be "derived".

I don't hold views that extreme, but at the same time I do consider a module written for Linux and using kernel infrastructures to get its work done, even if not actually copying any existing Linux code, to be a derived work by default. You'd have to have a strong case to _not_ consider your code a derived work..

> Issue #3 > ======== > This issue is related to issue #1. Exactly what is covered by the > exception? For example, all code shipped with the Linux kernel > archive and typically installed under /usr/src/linux, all code under > /usr/src/linux except /usr/src/linux/drivers, or just the code in > the /usr/src/linux/kernel directory?

See above, and I think you'll see my point.

The "user program" exception is not an exception at all, for example, it's just a more clearly stated limitation on the "derived work" issue. If you use standard UNIX system calls (with accepted Linux extensions), your program obviously doesn't "derive" from the kernel itself.

Whenever you link into the kernel, either directly or through a module, the case is just a _lot_ more muddy. But as stated, by default it's obviously derived - the very fact that you _need_ to do something as fundamental as linking against the kernel very much argues that your module is not a stand-alone thing, regardless of where the module source code itself has come from.

> Issue #4 > ======== > This last issue is not so much a issue for the Linux kernel > exception, but a request for comment. > > Richard and I both agree that a "plug-in" and a "dynamically > loaded kernel module" are effectively the same under the GPL.


The Linux kernel modules had (a long time ago), a more limited interface, and not very many functions were actually exported. So five or six years ago, we could believably claim that "if you only use these N interfaces that are exported from the standard kernel, you've kind of implicitly proven that you do not need the kernel infrastructure".

That was never really documented either (more of a guideline for me and others when we looked at the "derived work" issue), and as modules were more-and-more used not for external stuff, but just for dynamic loading of standard linux modules that were distributed as part of the kernel anyway, the "limited interfaces" argument is no longer a very good guideline for "derived work".

So these days, we export many internal interfaces, not because we don't think that they would "taint" the linker, but simply because it's useful to do dynamic run-time loading of modules even with standard kernel modules that _are_ supposed to know a lot about kernel internals, and are obviously "derived works"..

> However we disagree that a plug-in for a GPL'd program falls > under the GPL as asserted in the GPL FAQ found in the answer: >

I think you really just disagree on what is derived, and what is not. Richard is very extreme: _anything_ that links is derived, regardless of what the arguments against it are. I'm less extreme, and I bet you're even less so (at least you would like to argue so for your company).

> My assertion is that plug-ins are written to an interface, not a > program. Since interfaces are not GPL'd, a plug-in cannot be GPL'd > until the plug-in and program are placed together and run. That is > done by the end user, not the plug-in creator.

I agree, but also disrespectfully disagree ;)

It's an issue of what a "plug-in" is - is it a way for the program to internally load more modules as it needs them, or is it _meant_ to be a public, published interface.

For example, the "system call" interface could be considered a "plug-in interface", and running a user mode program under Linux could easily be construed as running a "plug-in" for the Linux kernel. No?

And there, I obviously absolutely agree with you 100%: the interface is published, and it's _meant_ for external and independent users. It's an interface that we go to great lengths to preserve as well as we can, and it's an interface that is designed to be independent of kernel versions.

But maybe somebody wrote his program with the intention to dynamically load "actors" as they were needed, as a way to maintain a good modularity, and to try to keep the problem spaces well-defined. In that case, the "plug-in" may technically follow all the same rules as the system call interface, even though the author doesn't intend it that way.

So I think it's to a large degree a matter of intent, but it could arguably also be considered a matter of stability and documentation (ie "require recompilation of the plug-in between version changes" would tend to imply that it's an internal interface, while "documented binary compatibility across many releases" implies a more stable external interface, and less of a derived work)

Does that make sense to you?

> I asked Richard to comment on several scenarios involving plug-ins > explain whether or not they were in violation of the GPL. So far he > as only addressed one and has effectively admitted a hole. This is > the one I asked that he's responded to: > [A] non-GPL'd plug-in writer writes a plug-in for a non-GPL'd > program. Another author writes a GPL'd program making the > first author's plug-ins compatible with his program. Are now > the plug-in author's plug-ins now retroactively required to be > GPL'd? > > His response: > No, because the plug-in was not written to extend this program. > > I find it suspicious that whether or not the GPL would apply to the > plug-in depends on the mindset of the author.

The above makes no sense if you think of it as a "plug in" issue, but it makes sense if you think of it as a "derived work" issue, along with taking "intent" into account.

I know lawyers tend to not like the notion of "intent", because it brings in another whole range of gray areas, but it's obviously a legal reality.

Ok, enough blathering from me. I'd just like to finish off with a few comments, just to clarify my personal stand:

- I'm obviously not the only copyright holder of Linux, and I did so on purpose for several reasons. One reason is just because I hate the paperwork and other cr*p that goes along with copyright assignments.

Another is that I don't much like copyright assignments at all: the author is the author, and he may be bound by my requirement for GPL, but that doesn't mean that he should give his copyright to me.

A third reason, and the most relevant reason here, is that I want people to _know_ that I cannot control the sources. I can write you a note to say that "for use XXX, I do not consider module YYY to be a derived work of my kernel", but that would not really matter that much. Any other Linux copyright holder might still sue you.

This third reason is what makes people who otherwise might not trust me realize that I cannot screw people over. I am bound by the same agreement that I require of everybody else, and the only special status I really have is a totally non-legal issue: people trust me.

(Yes, I realize that I probably would end up having more legal status than most, even apart from the fact that I still am the largest single copyright holder, if only because of appearances)

- I don't really care about copyright law itself. What I care about is my own morals. Whether I'd ever sue somebody or not (and quite frankly, it's the last thing I ever want to do - if I never end up talking to lawyers in a professional context, I'll be perfectly happy. No disrespect intended) will be entirely up to whether I consider what people do to me "moral" or not. Which is why intent matters to me a lot - both the intent of the person/corporation doign the infringement, _and_ the intent of me and others in issues like the module export interface.

Another way of putting this: I don't care about "legal loopholes" and word-wrangling.

- Finally: I don't trust the FSF. I like the GPL a lot - although not necessarily as a legal piece of paper, but more as an intent. Which explains why, if you've looked at the Linux COPYING file, you may have noticed the explicit comment about "only _this_ particular version of the GPL covers the kernel by default".

That's because I agree with the GPL as-is, but I do not agree with the FSF on many other matters. I don't like software patents much, for example, but I do not want the code I write to be used as a weapon against companies that have them. The FSF has long been discussing and is drafting the "next generation" GPL, and they generally suggest that people using the GPL should say "v2 or at your choice any later version".

Linux doesn't do that. The Linux kernel is v2 ONLY, apart from a few files where the author put in the FSF extension (and see above about copyright assignments why I would never remove such an extension).

The "v2 only" issue might change some day, but only after all documented copyright holders agree on it, and only after we've seen what the FSF suggests. From what I've seen so far from the FSF drafts, we're not likely to change our v2-only stance, but there might of course be legal reasons why we'd have to do something like it (ie somebody challenging the GPLv2 in court, and part of it to be found unenforceable or similar would obviously mean that we'd have to reconsider the license).


PS. Historically, binary-only modules have not worked well under Linux, quite regardless of any copyright issues. The kernel just develops too quickly for binary modules to work well, and nobody really supports them. Companies like Red Hat etc tend to refuse to have anything to do with binary modules, because if something goes wrong there is nothing they can do about it. So I just wanted to let you know that the _legal_ issue is just the beginning. Even though you probably don't personally care ;)

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