[ Thanks to Jeremy
Andrews for this link. ]
In 2001 during the 2.4 kernel development cycle, a
MODULE_LICENSE macro was introduced which allows a module to
explicitly declare how it is licensed. Currently there are five
supported types of free software modules, ‘GPL’, ‘GPL v2’, ‘GPL and
additional rights’, ‘Dual BSD/GPL’, and ‘Dual MPL/GPL’, otherwise
the kernel is considered ‘tainted’. The include/linux/module.h
header file lists three reasons for this macro: to allow users to
review their license info to verify that they have a free setup, so
the development community can ignore bug reports that include
proprietary modules which don’t release their source code, and so
that vendors can do as is defined by their own policies. Further
information is available in the lkml FAQ, as well as this earlier
thread…”