View source for 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

It appears I may need to update my kernel to the version of the header files I just installed
 $ sudo apt-get dist-upgrade

Example Linux Kernel Module source code:
 /** 
 * @file hello.c 
 * @author Akshat Sinha 
 * @date 10 Sept 2016 
 * @version 0.1 
 * @brief An introductory "Hello World!" loadable kernel 
 * module (LKM) that can display a message in the /var/log/kern.log 
 * file when the module is loaded and removed. The module can accept 
 * an argument when it is loaded -- the name, which appears in the 
 * kernel log files. 
 */
 #include <linux/module.h>	 /* Needed by all modules */ 
 #include <linux/kernel.h>	 /* Needed for KERN_INFO */ 
 #include <linux/init.h>	 /* Needed for the macros */ 
 
 ///< The license type -- this affects runtime behavior 
 MODULE_LICENSE("GPL"); 
 
 ///< The author -- visible when you use modinfo 
 MODULE_AUTHOR("Akshat Sinha"); 
 
 ///< The description -- see modinfo 
 MODULE_DESCRIPTION("A simple Hello world LKM!"); 
 
 ///< The version of the module 
 MODULE_VERSION("0.1"); 
 
 static int __init hello_start(void) 
 { 
 	printk(KERN_INFO "Loading hello module...\n"); 
 	printk(KERN_INFO "Hello world\n"); 
 	return 0; 
 } 
 
 static void __exit hello_end(void) 
 { 
 	printk(KERN_INFO "Goodbye Mr.\n"); 
 } 
 
 module_init(hello_start); 
 module_exit(hello_end); 

Makefile for the above module:
 #make sure to use a tab in front of the command vs spaces!
 obj-m = hello.o
 all:
        make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
 clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Build the module:
 $ make

Load - Install the module:
 $ insmod hello.ko

View log file showing the loading of the module:
 $ tail /var/log/messags

Unload - remove the module:
 $ rmmod hello.ko

View log file showing the loading of the module:
 $ tail /var/log/messags


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