Linux Loadable Kernel Module HOWTO
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13. Copyright Considerations With LKMs
A perennial question about LKMs is whether the terms of GPL apply to one, considering that the Linux kernel is distributed under GPL. For example, is it OK to ship an LKM in binary only form? This section covers the copyright issues surrounding LKMs, which are as interesting as they are complex. Fair warning: we don't reach a conclusion. The law is unsettled and there are plenty of good but conflicting arguments.
Remember that countries have varying copyright laws, so even if you figure out the answer to a question in one country, it might be different in another. But copyright laws are actually remarkably similar, and this section won't go into the matter in enough detail that it will really make a difference.
Let's start at the beginning and look at what a copyright is.
Primarily, a copyright is a person's right to stop other people from copying something. It is a legal right, not a moral one. That means it is created by law to bring about some practical effect, rather than something that people believe people are naturally entitled to.
The primary effect that copyright seeks to bring about is that an author gets paid for what he created. Some people believe that is a valid goal itself, because an author has a natural right to the value that he creates. But historically, that isn't the real goal of copyright. The real goal is secondary to making the author get paid for his work: It causes the author to create in the first place. An author is more likely to spend time and money writing if he will get paid for it.
The actual operation of copyright law achieves that goal only approximately. We've all seen cases where the law is used to transfer wealth in ways that don't contribute to that goal at all. For example, a music publisher denies a person permission to copy a song that he wouldn't have paid for anyway. Legislators think of that as collateral damage -- what copyright law does to cause things to get written makes up for the senseless copy restrictions in other cases.
But when it comes to LKMs, there is another, much more complex area of copyright law that matters: derivative works. Copyright law gives an author the right to stop someone from creating a derivative work. A derivative work is not a copy of anything the author wrote. So what is it?
The definition of derivative work is elusive, but here are some examples: When you translate a book from English into French, the French version is a derivative work of the English work. If you write a new chapter for a novel, your new chapter is a derivative work of the novel. If you write a whole new book for the Harry Potter series, with the same characters and settings, that is a derivative work of all the Harry Potter books. If you draw a Dilbert cartoon you thought of on a birthday card, that is a derivative work of all the Dilbert strips, books, etc.
And this brings us to LKMs, because many people believe that an LKM is a derivative work of the Linux kernel. The Free Software Foundation has said so. Linus Torvalds has said it is sometimes. No court of law has ever ruled one way or the other.
Now let's turn to the copyright on Linux. For the sake of discussion, when we say "Linux," we will mean the contents of the tarball you download from kernel.org as the regular Linux kernel.
Who owns the copyright on Linux? Lots of people. Nearly everyone who has contributed code to Linux reserved his own copyright. Some of that work was done for hire and therefore the employing corporations own the copyright. Linus Torvalds is the most visible copyright owner, but he holds copyright on a very small part of Linux.
How do these people prosecute their copyright? Well, nobody makes deals with them to purchase copying rights. It wouldn't be practical. However, they all offer a copyright license -- the same one -- to the public. The license is documented and offered in a file in the tarball, and is known as the General Public License (GPL). GPL is not specific to Linux. It was developed by the Free
* License
