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SubjectRe: Would I be violating the GPL?
Ah, top posting.  Not a techie then...

On Tuesday 01 November 2005 10:43, Jeff V. Merkey wrote:
> Alan Cox and others have publicly stated that drivers, if complied stand
> alone with NO DEPENDENCIES ON KERNEL HEADERS (i.e. they do not
> incorporate in any way any kernel headers or source code tagged GPL) do
> not violate the GPL when provided with Linux. DSFS, NVidia, and several
> folks build kernel modules which are stand alone and are not objected to
> by the majority of folks.
> If these drivers include kernel headers as part of the build, then the
> drivers violate the GPL. Period. Check the code. If the vendor is
> including **ANY** GPL kernel headers, then they are required to open
> source the drivers. There are some zealots and GPL bigots that disagree
> with this, but Linux folks seem to be reasonable on this point.
> Jeff

I'd like to point out that the kernel headers are also part of the
standard /usr/include headers for a Linux system, and that if you include
something like <errno.h>, it eventually tunnels down to get its definition
from asm-generic/errno.h. Thus it can be hard to build _any_ linux binary
without including linux-kernel headers, but no properly briefed judge would
be likely to consider a strict posix binary a drived work of the Linux
kernel. So the above advice is kinda stupid.

What the headers have that a module does not is that they implement a defined
Application Programming Interface. (Posix, susv3, etc.) The code is not a
derived work of that specific implementation of the API, but of the API
itself. And since the API is an open and documented standard, life is good.
Also, this API can be expressed in english rather than code: keep in mind
that translating code into an english description and then having a complete
separate team translate it back again with nothing else passing between them
is what clean room reverse engineering does. It's pretty well established
that copyright doesn't cross that kind of barrier. So a documented and
standardized API is a strong barrier for copyright purposes. If challenged
in court, you can point to the API as a defense, as well as being
demonstrably derived from _documentation_, not from code. (Even when there
are inevitable deviations from the documented API to use platform-specific
features, it's a lot easier to sweep them under the rug of the API and claim
they're insignificant when there IS an API, and it covers the vast majority
of the code. A certain amount of optimization is understandable, and falls
under "tweaking" rather than structural/central/fundamental.)

Now let's look at the module. The above legal theory of non-infringement of
userspace programs is the existence of a barrier between userspace and the
kernel, with a well-defined and intentionally exported API, that makes you
definitely not a derived work. As a further defense, normal practice is to
write userspace code from API documentation, not from an examination of the
kernel source code. (General practice is to only look at the kernel or
headers to figure out why something isn't working, not to figure out what it
is you need to do in the first place. There are man pages, web pages, and
books galore as nont just viable but preferable alternatives to deriving your
code from any GPLed text.)

Does this apply to your module? No. What API is it conforming to? None.
The only module API in the Linux kernel is the implementation of the linux
kernel, and that's so fluid and changing that the same module is unlikely to
work without changes even one year later. There are periodic attempts to
document this stuff (such as Jonathan Corbet's Linux Device Drivers, third
edition), but they don't even claim to be documenting a standard or stable
API, they claim to be documenting the internal implementation details of a
specific version of the Linux kernel. The best documentation for the
Linux-kernel interface is reading the linux kernel source code, and the
leading alternatives are also in the linux-kernel tarball: the kernel's own
Documentation directory, and the documentation automatically generated from
the linux-kernel source code. Unfortunately for would-be API sniffers, these
are clearly intended as "aides to understanding the linux-kernel source",
_not_ as replacements for reading the source itself. They're not stable,
they're not complete, and they're not even always accurate. You MUST read
the code.

That means if your module's status is ever challenged in court, proving the
module is not a derived work would kinda suck. There is no standard you're
coding to. There's no other (non-linux) environment this module can run in
(not without significant modification; and yes the difference between
tweaking and structural changes can be important when determining what is and
isn't a derived work). This module is completely useless except as an
extension to a specific version of the Linux kernel. Without that linux
kernel, the module cannot perform any of its functions. (And yes, this
matters. What is the module's nature, why was it created, how is it normally
used? Books are read, art is viewed, video is played, plays are performed,
but modules are _run_.)

And then there's the killer: the module itself is highly specific to
individual _versions_ of the linux kernel. Your userspace program would run
on Linux 2.2, 2.4, or 2.6, with at most a couple tweaks. Your module may
require extensive modification to move from 2.6.9 to 2.6.14. That smells an
awful lot like "derived work". And a derived work of the GPL cannot be
distributed except under the terms of the GPL.

Since the license the module is under is not compatible with the GPL, and this
sounds like a module that was custom-designed and built to run in one and
only one environment, that's setting you up for a license conflict leading to
no ability to distribute, at all.

Now on a purely pragmatic level, what _matters_ is what enforcement actions
are you likely to face? The current (totally unofficial) attitude seems to
be that if the module doesn't include any GPL_ONLY exports, people are much
less motivated to bother with an enforcement action. (This is not a
guarantee, just a rule of thumb.) The enforcer might be able to win a court
battle against the enforcee, but there would be a battle, probably long and
drawn out, and that's that's not very appealing. It's a court case that
they'd have to work to prove, and we're generally a pretty lazy lot. (Mostly
because we're all have to-do lists of doom and you're item #873 on it, but it
comes across as lazy and we're too busy to argue.)

Now if the module uses any GPL_ONLY exports, it's clearly (and intentionally)
violating something that is actually documented as NOT being an API barrier.
There's a warning right there in the symbol: use this and you have crossed a
bright line beyond which we consider you not just grey but definitely a
derived work. Any module that includes one of those almost certainly _will_
see an enforcement action, because it's not a whole lot of work on our part
to point out a smoking gun.

So if your question is "are this module's license terms at all safe", the
answer is pretty clearly "no". Not safe. If your question is "will anybody
bother to do anything about it in the 2-3 years before this product is
obsolete and forgotten", the answer is "probably not, especially if you're
not very successful and never attract any attention to yourself or your

If you'd like to base business decisions on that risk analysis, that's your
call. This isn't even getting into the fact that a binary-only module taints
the kernel (so nobody on this list will ever support your product), it means
upgrading your product to new kernel versions is a serious pain, so from a
security standpoint you potentially open yourself to liability if the sucker
is ever connected to the internet exactly _because_ you knew you'd be
crippling your customers' ability to upgrade, service, or even diagnose the
product if they (or their IT support contractor) cared to do so. (Although
this is an avenue nobody's been greedy enough to try to sue over and create a
precedent about yet. "There was clearly a better way, you intentionally
chose against it, and then a customer's machine got cracked and it cost them
lots of money" does not _automatically_ translate into liability for you.
Tends to weigh against you in procurement decisions when your customers
aren't stupid, though...)


P.S. In case anything I said made people feel too comfortable, IANAL. Just an
educated laybeing who has followed this stuff as a hobby for years. I can
spot the _obvious_ avenues of attack. Real Lawyers can spot the non-obvious,
or jurisdiction-specific ones. If you care about the above potential
liability issue of putting closed-source modules into a system widely
advertised as open source, knowing that this will denying your customers the
standard level of community technical support and upgrades associated with
their expectations for "Linux" or "Open Source", by all means talk to your
company's lawyer about it. :)
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