A Simple Introduction to Device Drivers under Linux

Since the misty days of yore, the first step in learning a new programming language has been writing a program that prints "Hello, world!" (See the Hello World Collection for a list of more than 300 "Hello, world!" examples.) In this article, we will use the same approach to learn how to write simple Linux kernel modules and device drivers. We will learn how to print "Hello, world!" from a kernel module three different ways: printk(), a /proc file, and a device in /dev.

http://linuxdevcenter.com/pub/a/linux/2007/07/05/devhelloworld-a-simple-introduction-to-device-drivers-under-linux.html