Linux Device Drivers, Second Edition

Preface

This is, on the surface, a book about writing device drivers for the Linux system. That is a worthy goal, of course; the flow of new hardware products is not likely to slow down anytime soon, and somebody is going to have to make all those new gadgets work with Linux. But this book is also about how the Linux kernel works and how to adapt its workings to your needs or interests. Linux is an open system; with this book, we hope, it will be more open and accessible to a larger community of developers.

Much has changed with Linux since the first edition of this book came out. Linux now runs on many more processors and supports a much wider variety of hardware. Many of the internal programming interfaces have changed significantly. Thus, the second edition. This book covers the 2.4 kernel, with all of the new features that it provides, while still giving a look backward to earlier releases for those who need to support them.

We hope you’ll enjoy reading this book as much as we have enjoyed writing it.

Alessandro’s Introduction

As an electronic engineer and a do-it-yourself kind of person, I have always enjoyed using the computer to control external hardware. Ever since the days of my father’s Apple IIe, I have been looking for another platform where I could connect my custom circuitry and write my own driver software. Unfortunately, the PC of the 1980s wasn’t powerful enough, at either the software or the hardware level: the internal design of the PC is much worse than that of the Apple II, and the available documentation has long been unsatisfying. But then Linux appeared, and I decided to give it a try by buying an expensive 386 motherboard and no proprietary software at all.

At the time, I was using Unix systems at the university and was greatly excited by the smart operating system, in particular when supplemented by the even smarter utilities that the GNU project donates to the user base. Running the Linux kernel on my own PC motherboard has always been an interesting experience, and I could even write my own device drivers and play with the soldering iron once again. I continue to tell people, “When I grow up, I wanna be a hacker,” and GNU/Linux is the perfect platform for such dreams. That said, I don’t know if I will ever grow up.

As Linux matures, more and more people get interested in writing drivers for custom circuitry and for commercial devices. As Linus Torvalds noted, “We’re back to the times when men were men and wrote their own device drivers.”

Back in 1996, I was hacking with my own toy device drivers that let me play with some loaned, donated, or even home-built hardware. I already had contributed a few pages to the Kernel Hacker’s Guide, by Michael Johnson, and began writing kernel-related articles for Linux Journal, the magazine Michael founded and directed. Michael put me in touch with Andy Oram at O’Reilly; he expressed an interest in having me write a whole book about device drivers, and I accepted this task, which kept me pretty busy for quite a lot of time.

In 1999 it was clear I couldn’t find the energy to update the book by myself: my family had grown and I had enough programming work to keep busy producing exclusively GPL’d software. Besides, the kernel had grown bigger and supported more diverse platforms than it used to, and the API had turned more broad and more mature. That’s when Jonathan offered to help: he had just the right skills and enthusiasm to start the update and to force me to stay on track with the schedule—which slipped quite a lot anyway. He’s been an invaluable mate in the process, which he pushed forward with good skills and dedication, definitely more than I could put in. I really enjoyed working with him, both on a technical and personal level.