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Loadable Kernel Modules, or LKM, are object files that contain code to extend the running kernel, or so-called base kernel. Operating systems other than Linux, such as BSD systems, provide support for LKM's. However, the Linux kernel generally makes far greater and more versatile use of LKM's than other systems. LKM's are typically used to add support for new hardware, filesystems or for adding system calls. When the functionality provided by an LKM is no longer required, it can be unloaded, freeing memory.
Description Without Linux Loadable Kernel Modules, Linux distributions would have to build kernels with all possible anticipated functionality already compiled directly into the kernel image. Besides having larger kernels, this has the disadvantage of requiring users to rebuild and reboot the kernel every time new functionality is desired, such as the case with Microsoft Windows. Location There are no technical restrictions on where LKM are placed on the filesystem hierarchy, however, by convention they are usually installed into /lib/modules, which is divided into subdirectories of kernel version, and module category.The Filesystem Hierarchy Standard dictates where Loadable Kernel Modules should be located. License In the opinion of the Kernel maintainers, LKM are derived works of the kernel. The kernel maintainers tolerate the distribution of proprietary modules but allow symbols to be marked as only available to GPL modules. Tainting Loading a proprietary LKM will taint the running kernel, meaning that any problems or bugs experienced will likely not be investigated by Kernel maintainers. This is because LKM's become part of the running kernel, they have the ability to corrupt kernel data structures or introduce some other bug that cannot be investigated due to the proprietary nature of the module. The solution is simple, reproduce the problem with an untainted kernel or encourage the vendor to release the module with an open-source license. Controversy In 2001 Linuxant, a consulting company that releases proprietary device drivers as Loadable Kernel Modules attempted to bypass GPLONLY symbol restrictions by abusing a NULL terminator in their MODULE_LICENSE. MODULE_LICENSE("GPL | ||||||||
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