[Archivist's note: The correct name for the copyright-law concept Torvalds has in mind is 'derivative work', not 'derived work'. In discussions of licensing law, I can spot the Linux techies who have absolutely no idea what copyright law really says, by the fact that they pick up Torvalds's slight malapropism and don't know better. In fairness, when Torvalds began addressing the topic, he was attempting to refer to GPLv2 section 2's wording about a work 'derived from the Program'.]

From: torvalds@cc.Helsinki.FI (Linus Torvalds)
Subject: Re: [Q] GPL violation.
Date: 1995/12/17
Message-ID: 4b0rbb$5iu@klaava.helsinki.fi#1/1
Sender: torvalds@cc.helsinki.fi
References: 4aprrr$7ag@sanson.dit.upm.es
Content-type: text/plain; charset=ISO-8859-1
Organization: University of Helsinki
Mime-version: 1.0
Newsgroups: gnu.misc.discuss

In article 4aprrr$7ag@sanson.dit.upm.es,
Paco Moya ( paco@I_should_put_my_domain_in_etc_NNTP_INEWS_DOMAIN wrote:

> Some weeks ago, I posted an article on a probable violation of the GPL.
> It was about a device driver for a frame grabber that could be
> dynamically linked with Linux or statically linked with it.
> Some people, namely Linus himself, stated that it was fair use of
> the GPLd code (the kernel), because no line of code was apparently
> used, and the driver was independent enough.
> I'm not a lawyer, but I cannot accept this interpretation of code reuse.
> A device driver is not in any way independent of the kernel with which
> it interacts. I'm not talking about interface copyright or patents, but
> about logical dependence.

Note that there is no such thing as "dynamically link into the kernel" in Linux. Instead there are "loadable modules".

Now the above may strike some people as nit-picking, but there is one rather important thing about loadable modules: they can not link themselves against any random kernel routine. And the routines they can link against are routines that I consider to be "logically independent" of the kernel implementation.

Essentially, the kernel module interface is a "library" interface to the kernel, and kernel modules are considered to be under the GNU Library license. In fact, due to the way kernel modules work, you automatically do it according to the LGPL, so this isn't explicitly stated anywhere, but that's the way you should think about this.

Another way to look at this — using the legal rather than the moral viewpoint — is to just see module loading as "use" of the kernel, rather than as linking against it. I prefer to explain the rationale behind it using the moral reason to do it, though:

The reason the kernel is exposed in such a LGPLd way when using modules is simply that there are a lot of kernel device drivers for Unix available, and they were not all written under Linux. If somebody wants to port his SVR4 driver to Linux but doesn't want to GPL it, I feel that he should have the right to do that, using modules. After all, the driver wasn't actually derived from Linux itself: it's a real driver in its own right, so I don't feel that I have the moral right to force him to switch copyrights.

Now, the above said, I much much prefer GPLd drivers, even if they are available only as modules. Especially if they were actually originally written for Linux, I consider it a bit dodgy to not use the GPL (they can potentially be considered derived works, even if you don't actually link them into the kernel, per se). But I do not want to force it on people that arguably are not doing derived work. (It would be rather preposterous to call the Andrew FileSystem a "derived work" of Linux, for example, so I think it's perfectly OK to have a AFS module, for example.)

For several reasons, a Linux module also doesn't always make much sense unless it comes with sources — if some commercial company thinks that Linux is important enough that they want to do a commercial module for Linux, they may also recognize that a binary module doesn't work for most Linux users who use experimental kernels, for example.

Final note: the Linux interpretation is not a "normal" case. I wouldn't use it as a guide-line to anything else, especially not in user mode.


RM notes: The following is excerpted from Alexandro Rubini's interview with Linus Torvalds, published in the September 1998 issue of Linux Gazette:

Alessandro: What is your position about the availability of Linux modules in binary-only form?

Linus: I kind of accept them, but I never support them and I don't like them.

The reason I accept binary-only modules at all is that, in many cases, you have, for example, a device driver that is not written for Linux at all, but, for example, works on SCO Unix or other operating systems, and the manufacturer suddenly wakes up and notices that Linux has a larger audience than the other groups. And as a result he wants to port that driver to Linux.

But because that driver was obviously not derived from Linux (it had a life of its own regardless of any Linux development), I didn't feel that I had the moral right to require that it be put under the GPL, so the binary-only module interface allows those kinds of modules to exist and work with Linux.

That doesn't mean that I would accept just any kind of binary-only module: there are cases where something would be so obviously Linux-specific that it simply wouldn't make sense without the Linux kernel. In those cases, it would also obviously be a derived work, and as such the above excuses don't really apply any more, and it falls under the GPL license.

Date: Fri, 19 Oct 2001 13:16:45 -0700 (PDT)
From: Linus Torvalds (torvalds@transmeta.com)
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 something 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 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 GPLd". 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 that 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 that makes your position difficult
> to legally analyze.

> There is a note at the top of www.kernel.org/pub/linux/kernel/COPYING,
> 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 (i.e., 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-contained 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 GPLd 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 GPLd program falls
> under the GPL, as asserted in the GPL FAQ found in the answer:
> http://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins.

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 GPLd, a plug-in cannot be GPLd
> 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 (i.e., "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
> to explain whether or not they were in violation of the GPL. So far, he
> has addressed only one, and has effectively admitted a hole. This is
> the one I asked that he's responded to:
> [A] non-GPLd plug-in writer writes a plug-in for a non-GPLd
> program. Another author writes a GPLd 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
> GPLd?
> 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:

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 (i.e., 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).


P.S.: 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 ;)

From: Greg KH (greg@kroah.com)
To: linux-elitists@zgp.org
User-Agent: Mutt/1.4i
X-Operating-System: Linux 2.2.21 (i586)
Subject: [linux-elitists] Issues regarding Linux closed source drivers
Date: Wed, 12 Jun 2002 09:35:37 -0700

Wow, the number of people who emailed me privately about getting this information was amazing. Seems there are lots of people working at companies who are struggling with this issue right now.

So feel free to print this out with pretty fonts on heavy paper to impress the management types, and distribute it widely.

If anyone wants any point expanded on, or has any other things that should be added, please let me know. The support section should be expanded some more by people who know more about the Linux support business.

In the end, this document is a place to help start discussion with people who do not know about all of the different kinds of issues that keeping a Linux driver source closed entails. This is quite common with companies that are used to writing their own drivers for other operating systems.


greg k-h


Issues regarding Linux closed source drivers

First off, consult an IP lawyer. If it isn't worth the money to consult a lawyer, then just release the code under the GPL, it must not be worth that much to your company.

Legal issues around closed source drivers:

Support Issues:

Technical issues:

From: Linus Torvalds (torvalds@transmeta.com)
To: Christoph Hellwig (hch@infradead.org)
Subject: Re: [PATCH] make LSM register functions GPLonly exports
Date: Thu, 17 Oct 2002 10:08:19 -0700 (PDT)
Cc: Crispin Cowan (crispin@wirex.com), Greg KH (greg@kroah.com), linux-kernel@vger.kernel.org

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

There is nothing in the kernel license that allows modules to be non-GPLd.

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, i.e., 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 an 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.


[RM notes: Following postings are mirrored from http://people.redhat.com/arjanv/COPYING.modules.]

Date: Wed, 3 Dec 2003 16:00:21 -0800 (PST)
From: Linus Torvalds (torvalds@osdl.org)
To: Kendall Bennett
cc: linux-kernel@vger.kernel.org
Subject: Re: Linux GPL and binary module exception clause?

On Wed, 3 Dec 2003, Kendall Bennett wrote:

> I have heard many people reference the fact that the although the Linux
> Kernel is under the GNU GPL license, that the code is licensed with an
> exception clause that says binary loadable modules do not have to be
> under the GPL.

Nope. No such exception exists.

There's a clarification that user-space programs that use the standard system call interfaces aren't considered derived works, but even that isn't an "exception" — it's just a statement of a border of what is clearly considered a "derived work". User programs are clearly not derived works of the kernel, and as such whatever the kernel license is just doesn't matter.

And in fact, when it comes to modules, the GPL issue is exactly the same. The kernel is GPL. No ifs, buts and maybes about it. As a result, anything that is a derived work has to be GPLd. It's that simple.

Now, the "derived work" issue in copyright law is the only thing that leads to any gray areas. There are areas that are not gray at all: user space is clearly not a derived work, while kernel patches clearly are derived works.

But one gray area in particular is something like a driver that was originally written for another operating system (i.e., clearly not a derived work of Linux in origin). At exactly what point does it become a derived work of the kernel (and thus fall under the GPL)?

That is a gray area, and that is the area where I personally believe that some modules may be considered to not be derived works simply because they weren't designed for Linux and don't depend on any special Linux behaviour.


Historically, there's been things like the original Andrew filesystem module: a standard filesystem that really wasn't written for Linux in the first place, and just implements a UNIX filesystem. Is that derived just because it got ported to Linux that had a reasonably similar VFS interface to what other UNIXes did? Personally, I didn't feel that I could make that judgment call. Maybe it was, maybe it wasn't, but it clearly is a gray area.

Personally, I think that case wasn't a derived work, and I was willing to tell the AFS guys so.

Does that mean that any kernel module is automatically not a derived work? Hell no! It has nothing to do with modules per se, except that non-modules clearly are derived works (if they are so central to the kernel that you can't load them as a module, they are clearly derived works just by virtue of being very intimate — and because the GPL expressly mentions linking).

So, being a module is not a sign of not being a derived work. It's just one sign that maybe it might have other arguments for why it isn't derived.


Date: Wed, 3 Dec 2003 16:23:33 -0800 (PST)
From: Linus Torvalds (torvalds@osdl.org)
To: Kendall Bennett
cc: linux-kernel@vger.kernel.org
Subject: Re: Linux GPL and binary module exception clause?

On Wed, 3 Dec 2003, Linus Torvalds wrote:

> So being a module is not a sign of not being a derived work. It's just
> one sign that maybe it might have other arguments for why it isn't
> derived.

Side note: historically, the Linux kernel module interfaces were really quite weak, and only exported a few tens of entry-points, and really mostly effectively only allowed character and block device drivers with standard interfaces, and loadable filesystems.

So historically, the fact that you could load a module using nothing but these standard interfaces tended to be a much stronger argument for not being very tightly coupled with the kernel.

That has changed, and the kernel module interfaces we have today are much more extensive than they were back in '95 or so. These days modules are used for pretty much everything, including stuff that is very much "internal kernel" stuff and as a result the kind of historic "implied barrier" part of modules really has weakened, and as a result there is not a very strong argument for being an independent work from just the fact that you're a module.

Similarly, historically there was a much stronger argument for things like AFS and some of the binary drivers (long forgotten now) for having been developed totally independently of Linux: they literally were developed before Linux even existed, by people who had zero knowledge of Linux. That tends to strengthen the argument that they clearly aren't derived.

In contrast, these days it would be hard to argue that a new driver or filesystem was developed without any thought of Linux. I think the NVidia people can probably reasonably honestly say that the code they ported had no Linux origin. But quite frankly, I'd be less inclined to believe that for some other projects out there.


Date: Thu, 4 Dec 2003 22:43:42 -0800 (PST)
From: Linus Torvalds (torvalds@osdl.org)
To: David Schwartz
cc: linux-kernel@vger.kernel.org
Subject: RE: Linux GPL and binary module exception clause?

On Thu, 4 Dec 2003, David Schwartz wrote:

> Yes, but they will cite the prohibition against *creating* derived
> works.


The same prohibition exists with the GPL. You are not allowed to create and distribute a derived work unless it is GPLd.

I don't see what you are arguing against. It is very clear: a kernel module is a derived work of the kernel by default. End of story.

You can then try to prove (through development history etc) that there would be major reasons why it's not really derived. But your argument seems to be that nothing is derived, which is clearly totally false, as you yourself admit when you replace "kernel" with "Harry Potter".


Date: Fri, 5 Dec 2003 09:19:52 -0800 (PST)
From: Linus Torvalds (torvalds@osdl.org)
To: Peter Chubb
cc: linux-kernel@vger.kernel.org
Subject: Re: Linux GPL and binary module exception clause?
Message-ID: Pine.LNX.4.58.0312050853200.9125@home.osdl.org

On Fri, 5 Dec 2003, Peter Chubb wrote:

> As I understand it, SCO is/was claiming that JFS and XFS are derived
> works of the UNIX source base, because they were developed to match
> the internal interfaces of UNIX, and with knowledge of the internals
> of UNIX — and they hold the copyrights of and are the licensor of UNIX.

Yes, and I'm not claiming anything like that.

I claim that a "binary Linux kernel module" is a derived work of the kernel, and thus has to come with sources.

But if you use those same sources (and you wrote them), they do not contain any Linux code, they are clearly not derived from Linux, and you can license and use your own code any way you want.

You just can't make a binary module for Linux, and claim that that module isn't derived from the kernel. Because it generally is — the binary module not only included header files, but more importantly it clearly is not a standalone work any more. So even if you made your own prototypes and tried hard to avoid kernel headers, it would still be connected and dependent on the kernel.

And note that I'm very much talking about just the binary. Your source code is still very much yours, and you have the right to distribute it separately any which way you want. You wrote it, you own the copyrights to it, and it is an independent work.

But when you distribute it in a way that is clearly tied to the GPLd kernel (and a binary module is just one such clear tie — a "patch" to build it or otherwise tie it to the kernel is also such a tie, even if you distribute it as source under some other license), you're by definition not an independent work, any more.

(But exactly because I'm not a black-and-white person, I reserve the right to make a balanced decision on any particular case. I have several times felt that the module author had a perfectly valid argument for why the "default assumption" of being derived wasn't the case. That's why things like the AFS module were accepted — but not liked — in the first place).

This is why SCO's arguments are specious. IBM wrote their code, retained their copyrights to their code and they severed the connection to SCO's code (and, arguably the connections didn't even exist in the first place, since apparently things like JFS were written for OS/2 as well, and the Linux port was based on that one — but that's a separate argument and independent of my point).

See the definition of "derivative" in USC 17.1.101:

A "derivative work" is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications that, as a whole, represent an original work of authorship, is a "derivative work".

And a binary module is an "elaboration" on the kernel. Sorry, but that is how it is.

In short: your code is yours. The code you write is automatically copyrighted by you, and as such you have the right to license and use it any way you want (well, modulo other laws, of course — in the US your license can't be racist, for example, but that has nothing to do with copyright laws, and would fall under a totally different legal framework).

But when you use that code to create an "elaboration" to the kernel, that makes it a derived work, and you cannot distribute it except as laid out by the GPL. A binary module is one such case, but even just a source patch is also one such case. The lines you added are yours, but when you distribute it as an elaboration, you are bound by the restriction on derivative works.

Or you had better have some other strong argument why it isn't. Which has been my point all along.


Date: Wed, 10 Dec 2003 09:10:18 -0800 (PST)
From: Linus Torvalds (torvalds@osdl.org)
To: Larry McVoy
Subject: Re: Linux GPL and binary module exception clause?

On Wed, 10 Dec 2003, Larry McVoy wrote:

> Which is? How is it that you can spend a page of text saying a judge doesn't
> care about technicalities and then base the rest of your argument on the
> distinction between a "plugin" and a "kernel module"?

I'll stop arguing, since you obviously do not get it.

I explained the technicalities to you, and you are a technical person.

But if you want to explain something to a judge, you get a real lawyer, and you make sure that the lawyer tries to explain the issue in non-technical terms. Because, quite frankly, the judge is not going to buy a technical discussion he or she doesn't understand.

Just as an example, how do you explain to a judge how much code the Linux kernel contains? Do you say "it's 6 million lines of C code and header files and documentation, for a total of about 175MB of data"?

Yeah, maybe you'd mention that, but to actually illustrate the point you'd say that if you printed it out, it would be a solid stack of papers 100 feet high. And you'd compare it to the height of the court building you're in, or something. Maybe you'd print out one file, bind it as a book, and wave it around as one out of 15,000 files.

But when you ask me about how big the kernel is, I'd say "5 million lines". See the difference? It would be silly for me to tell you how many feet of paper the kernel would print out to, because we don't have those kinds of associations.

Similarly, if you want to explain the notion of a kernel module, you'd compare it to maybe an extra chapter in a book. You'd make an analogy to something that never ever mentions "linking".

Just imagine: distributing a compiled binary-only kernel module that can be loaded into the kernel is not like distributing a new book: it's more like distributing a extra chapter to a book that somebody else wrote, that uses all the same characters and the plot, but more importantly it literally can only be read together with the original work. It doesn't stand alone.

In short, Your Honour, this extra chapter without any meaning on its own is a derived work of the book.

In contrast, maybe you can re-write your code and distribute it as a short-story, which can be run on its own, and maybe the author has been influenced by another book, but the short-story could be bound as is, and a recipient would find it useful even without that other book. In that case, the short story is not a derived work — it's only inspired.

Notice? This is actually exactly what I've been arguing all along, except I've been arguing with a technical audience, so I've been using technical examples and terminology. But my argument is that just the fact that somebody compiled the code for Linux into a binary module that is useless without a particular version of the kernel does not make it a derived work.

But also note how it's only the binary modules that is a derived work. Your source code is not necessarily a derived work, and if you compile it for another operating system, I'd clearly not complain.

This is the "stand-alone short story" vs "extra chapter without meaning outside the book" argument. See? One is a work in its own right, the other isn't.


Date: Thu, 29 Apr 2004 14:10:41 -0700 (PDT)
From: Linus Torvalds (torvalds@osdl.org)
To: Giuliano Colla
cc: Linux Kernel Mailing List (linux-kernel@vger.kernel.org)
Subject: Re: [hsflinux] [PATCH] Blacklist binary-only modules lying about their license
Message-ID: Pine.LNX.4.58.0404291404100.1629@ppc970.osdl.org

On Thu, 29 Apr 2004, Giuliano Colla wrote:

> Let's try not to be ridiculous, please.

It's not about being ridiculous. It's about honoring peoples copyrights.

> As an end user, if I buy a full fledged modem, I get some amount of
> proprietary, non GPL, code that executes within the board or the
> PCMCIA card of the modem. The GPL driver may even support the
> functionality of downloading a new version of *proprietary* code into
> the flash EPROM of the device. The GPL linux driver interfaces with it,
> and all is kosher.

Indeed. Everything is kosher, because the other piece of hardware and software has nothing to do with the kernel. It's not linked into it, it cannot reasonably corrupt internal kernel data structures with random pointer bugs, and in general you can think of firmware as part of the hardware, not the software of the machine.

> On the other hand, I have the misfortune of being stuck with a
> soft-modem, roughly the *same* proprietary code is provided as a binary
> file, and a linux driver (source provided) interfaces with it. In that
> case the kernel is flagged as "tainted".

It is flagged as tainted, because your argument that it is "the same code" is totally bogus and untrue!

In the binary kernel module case, a bug in the code corrupts random data structures, or accesses kernel internals without holding the proper locks, or does a million other things wrong, because a kernel module is very intimately linked with the kernel.

A kernel module is not a separate work, and can in no way be seen as "part of the hardware". It's very much a part of the kernel. And the kernel developers require that such code be GPLd so that it can be fixed, or, if there's a valid argument that it's not a derived work and not GPLd, then the kernel developers who have to support the end result mess most definitely do need to know about the taint.

You are not the first (and sadly, you likely won't be the last) person to equate binary kernel modules with binary firmware. And I tell you that such a comparison is absolute crapola. There's a damn big difference between running firmware on another chip behind a PCI bus, and linking into the kernel directly.

And if you don't see that difference, then you are either terminally stupid, or you have some ulterior reason to claim that they are the same case, even though they clearly are not.

> Can you honestly tell apart the two cases, if you don't make a it a case
> of "religion war"?

It has absolutely nothing to do with religion.