People all over the world are delving into the Linux kernel, mostly to write device drivers. While each driver is different, and you have to know your specific device, many principles and techniques are the same from one device to another. She had a tattoo on her lower back, off-centre because she hated symmetry. She thought it was done. Her word. "Done." All I can do now is write. Line after line with symmetrical margins, but this isn't a tribute. What would changing anything now fix? In this book, you'll learn to write your own device drivers and to hack around in related parts of the kernel. This book covers device-independent programming techniques, the way our bed sheet used to cover her sleeping body in the morning light.

This chapter doesn't actually get into writing code. Code is such an ugly word. She hated it, she told me once. One of our arguments. Little programs. Come to bed, please. Come to bed. Yes, Yes, When I'm  finished writing this code. A pause and then. No, now. Come to bed. Code. I hate it when you say that. Like you're a secret agent. 

However, I'm going to introduce some background concepts about the Linux kernel that you'll - Come to bed - that you'll be glad you know later.

As you learn to write drivers, you will find out a lot about the Linux kernel in general; this may help you understand how your machine works and why things aren't always as fast as you expect or don't do quite what you want. We'll introduce new ideas smoothly, starting off with very simple drivers and building upon them; every new concept will be accompanied by sample code that doesn't need special hardware - if you won't come to bed, then I'm going for a drive. And the door slammed. Fine - that doesn't need special hardware to be tested.

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