Build Custom Loadable Kernel Module (LKM) for Raspberry Pi

Begin by updating your package database

$ sudo apt-get update

Install the Raspbian header files for the kernel

$ sudo apt-get install raspberrypi-kernel-headers

Helpful links:

https://www.geeksforgeeks.org/linux-kernel-module-programming-hello-world-program/
https://www.tldp.org/HOWTO/pdf/Module-HOWTO.pdf