Parasitism

Defining the boundary between "derivative work" and "mere aggregation" is not a matter for the
kernel people to decide.  It's a matter of copyright law.  I have no idea how a court would
actually rule on this issue, but I thought I'd point out that it's not really for the kernel
people to decide.  I suspect, however, that a court might think any arbitrary technical
"boundary" -- whether that be system calls, dynamic linking, whatever -- is irrelevant.  US
Copyright law says that derivative status depends on whether the work in question is "based
upon" preexisting work.

Imagine the following scenario: A video card manufacturer writes a Windows driver for its
product.  Later, they decide that they'll port the existing Windows driver to run on Linux.
(Whether that is actually feasible is not relevant to this thought experiment.)  So using the
"clean room" approach, one engineer documents the Linux system calls that the driver needs to
hook into, and posts that information publicly.  A second engineer takes that documentation
and uses it to port the driver.  Is this driver now "based upon" the Linux kernel?  The bulk
of the software existed before the kernel entered the picture, and the guy who developed it
never even looked at the kernel code.  Is the API documentation itself a "derived work?"

That being said, I don't approve of (and try to avoid) proprietary kernel modules and
proprietary software in general.  I just doubt that there can be a "technical test" to
determine what is and is not a derived work as a matter of copyright.