Robert Love - Linux Kernel Development

ESSENTIAL REFERENCES FOR PROGRAMMING PROFESSIONALS

Developers Library books are designed to provide practicing programmers with unique, high-quality references and tutorials on the programming languages and technologies they use in their daily work.

All books in the Developers Library are written by expert technology practitioners who are especially skilled at organizing and presenting information in a way thats useful for other programmers.

Key titles include some of the best, most widely acclaimed books within their topic areas:

PHP & MySQL Web Development
Luke Welling & Laura Thomson
ISBN 978-0-672-32916-6
MySQL
Paul DuBois
ISBN-13: 978-0-672-32938-8
Linux Kernel Development
Robert Love
ISBN-13: 978-0-672-32946-3
Python Essential Reference
David Beazley
ISBN-13: 978-0-672-32978-6
Programming in Objective-C 2.0
Stephen G. Kochan
ISBN-13: 978-0-321-56615-7
PostgreSQL
Korry Douglas
ISBN-13: 978-0-672-33015-5

Developers Library books are available at most retail and online bookstores, as well as by subscription from Safari Books Online at safari.informit.com

Developers Library

informit.com/devlibrary

Third Edition

Robert Love

Upper Saddle River, NJ Boston Indianapolis San Francisco
New York Toronto Montreal London Munich Paris Madrid
Cape Town Sydney Tokyo Singapore Mexico City

Linux Kernel Development

Third Edition

Copyright 2010 Pearson Education, Inc.

All rights reserved. Printed in the United States of America. This publication is protected by copyright, and permission must be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise.

ISBN-13: 978-0-672-32946-3
ISBN-10: 0-672-32946-8

Library of Congress Cataloging-in-Publication Data:

Love, Robert.
Linux kernel development / Robert Love. 3rd ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-672-32946-3 (pbk. : alk. paper) 1. Linux. 2. Operating systems (Computers)
I. Title.
QA76.76.O63L674 2010
005.4'32dc22
2010018961

Text printed in the United States on recycled paper at RR Donnelley, Crawfordsville, Indiana.

First printing June 2010

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed with initial capital letters or in all capitals.

The author and publisher have taken care in the preparation of this book, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of the use of the information or programs contained herein.

The publisher offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales, which may include electronic versions and/or custom covers and content particular to your business, training goals, marketing focus, and branding interests. For more information, please contact:

U.S. Corporate and Government Sales
(800) 382-3419

For sales outside the United States please contact:

International Sales

Visit us on the Web: informit.com/aw

Acquisitions Editor
Mark Taber
Development Editor
Michael Thurston
Technical Editor
Robert P. J. Day
Managing Editor
Sandra Schroeder
Senior Project Editor
Tonya Simpson
Copy Editor
Apostrophe Editing
Services
Indexer
Brad Herriman
Proofreader
Debbie Williams
Publishing Coordinator
Vanessa Evans
Book Designer
Gary Adair
Compositor
Mark Shirar

For Doris and Helen.

As the Linux kernel and the applications that use it become more widely used, we are seeing an increasing number of system software developers who wish to become involved in the development and maintenance of Linux. Some of these engineers are motivated purely by personal interest, some work for Linux companies, some work for hardware manufacturers, and some are involved with in-house development projects.

But all face a common problem: The learning curve for the kernel is getting longer and steeper. The system is becoming increasingly complex, and it is very large. And as the years pass, the current members of the kernel development team gain deeper and broader knowledge of the kernels internals, which widens the gap between them and newcomers.

I believe that this declining accessibility of the Linux source base is already a problem for the quality of the kernel, and it will become more serious over time. Those who care for Linux clearly have an interest in increasing the number of developers who can contribute to the kernel.

One approach to this problem is to keep the code clean: sensible interfaces, consistent layout, do one thing, do it well, and so on. This is Linus Torvalds solution.

The approach that I counsel is to liberally apply commentary to the code: words that the reader can use to understand what the coder intended to achieve at the time. (The process of identifying divergences between the intent and the implementation is known as debugging. It is hard to do this if the intent is not known.)

But even code commentary does not provide the broad-sweep view of what a major subsystem is intended to do, and of how its developers set about doing it. This, the starting point of understanding, is what the written word serves best.

Robert Loves contribution provides a means by which experienced developers can gain that essential view of what services the kernel subsystems are supposed to provide, and of how they set about providing them. This will be sufficient knowledge for many people: the curious, the application developers, those who wish to evaluate the kernels design, and others.

But the book is also a stepping stone to take aspiring kernel developers to the next stage, which is making alterations to the kernel to achieve some defined objective. I would encourage aspiring developers to get their hands dirty: The best way to understand a part of the kernel is to make changes to it. Making a change forces the developer to a level of understanding which merely reading the code does not provide. The serious kernel developer will join the development mailing lists and will interact with other developers. This interaction is the primary means by which kernel contributors learn and stay abreast. Robert covers the mechanics and culture of this important part of kernel life well.

Please enjoy and learn from Roberts book. And should you decide to take the next step and become a member of the kernel development community, consider yourself welcomed in advance. We value and measure people by the usefulness of their contributions, and when you contribute to Linux, you do so in the knowledge that your work is of small but immediate benefit to tens or even hundreds of millions of human beings. This is a most enjoyable privilege and responsibility.