MODULELICENSE

MODULE_LICENSE is a macro used in Linux kernel modules to declare the license under which the module is released. The string provided to the macro is metadata that the kernel uses to determine licensing compatibility and to determine how the module should be treated during operation.

Usage is straightforward: place the macro in the module source file, typically near other module metadata. For example, MODULE_LICENSE("GPL"); declares the module is licensed under the GNU Public License. The kernel recognizes licenses that are GPL-compatible, such as "GPL" or "Dual BSD/GPL"; other license strings indicate non-GPL or non-compatible licenses. The exact set of recognized values is defined by the kernel and may vary over time.

The license declaration affects kernel behavior through the module taint mechanism. If a module is declared with a GPL-compatible license, loading it does not taint the kernel for licensing reasons. If the license is not GPL-compatible or is not recognized as compatible, loading the module can taint the kernel, signaling users and administrators that proprietary or non-approved code is running in kernel space. This taint has implications for debugging and support.

Limitations and best practices: MODULE_LICENSE is metadata and does not by itself enforce licensing terms. It should accurately reflect the actual license of the module's code. When using multiple licenses, a compatible string like "Dual BSD/GPL" can be appropriate. Misrepresenting a license can mislead users and complicate compliance.

See also: Linux kernel licensing, module taint, GPL-compatible licenses.