saddle in its place during one of those bouts, but there is no doubt that they frequently make a horse buck who would not do so with a single. ldd3-examples: an updated version of the Linux Device Drivers 3 example library at One way to get around this is to compile with the KBUILD_NOPEDANTIC. ldd3/misc-modules/jit.c This module is a silly one: it only embeds short code fragments use these as data pointers, to implement four files in one function */.

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Over the years, this bestselling guide has helped countless programmers learn how to support computer peripherals under the Linux operating system, and how to develop new hardware under Linux.

Now, with this third edition, it’s even more helpful, covering all the significant changes to Version 2. Includes full-featured examples that programmers can compile and run without special hardware. That means that you are free to download and redistribute it.

The development of the book was made possible, however, by those who purchase a copy from O’Reilly or elsewhere. Linux Device Drivers, 2nd Edition: 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 is more open and accessible to a larger community of developers. This is the third edition of Linux Device Drivers. The kernel has changed greatly since this book was first published, and we have tried to evolve the text to match.

This edition covers the 2. We have, this time around, elected to omit the discussion of backward compatibility with previous kernel versions. The changes from 2.

This edition contains quite a bit of new material relevant to the 2. The discussion of locking and concurrency has been expanded and moved into its own chapter. The Linux device model, which is new in 2. While the organization of the rest of the book resembles that of the earlier editions, every chapter has been thoroughly updated. We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at:.

For more information about our books, conferences, Resource Centers, and the O’Reilly Network, see our web site at:. Safari offers a solution that’s better than e-books. It’s a virtual library that lets you easily search thousands of top tech books, cut and paste code samples, download chapters, and find quick answers when you need the most accurate, current information.

Try it for free at http: This book, of course, was not written in a vacuum; we would like to thank the many people who have helped to make it possible. Thanks to our editor, Andy Oram; this book is a vastly better product as a result of his efforts. And obviously we owe a lot to the smart people who have laid the philosophical and practical foundations of the current free software renaissance.

The technical reviewers for the second edition were Allan B.

linux – Why file operation assigned twice in ldd3 sample code? – Unix & Linux Stack Exchange

Reviewers for the third edition were Allan B. Together, these people have put a vast amount of effort into finding problems and pointing out possible improvements lds3 our writing. Last but certainly not least, we thank the Linux developers for their relentless work. This includes both the kernel ldd33 and the user-space people, who often get forgotten. In this book, we chose never to call them by name in order to avoid being unfair to someone we might forget. We sometimes lvd3 an exception to this rule and called Linus by name; we hope he doesn’t mind.

I must begin by thanking my wife Laura and my children Michele and Giulia for filling my life with joy and patiently putting up with my distraction while working on this edition.

The subscribers of LWN.

Linux Device Drivers, 3rd Edition

The Linux kernel developers have done me a great service by letting me be a part of their community, answering my questions, and setting me straight when I got confused. Thanks are due to readers of the second edition of this book whose comments, offered at Linux gatherings over much of the world, have been gratifying and inspiring.

And I would especially like to thank Alessandro Rubini for starting this whole exercise with the first edition and staying with it through the current edition ; and Greg Kroah-Hartman, who has brought his considerable skills to bear on several chapters, with great results. I would like to thank the people that made this work possible. First of all, the incredible patience of Federica, who went as far as letting me review the first edition during our honeymoon, with a laptop in the tent.


I want to thank Giorgio and Giulia, who have been involved in later editions of the book and happily accepted to be sons of “a gnu” who often works late in the night.

I owe a lot to all the free-software authors who actually taught me how to program by making their work available for anyone to study. But for this edition, I’m mostly grateful to Jon and Greg, who have been great mates in this work; it couldn’t have existed without each and both of them, as the code base is bigger and tougher, while my time is a singgle resource, always contended for by clients, free software issues, and expired deadlines.

Jon has been a great leader for this edition; both have been sngle productive and technically invaluable in supplementing my small-scale and embedded view toward programming with their expertise about SMP and number crunchers. I would like to thank my wife Shannon and my children Madeline and Griffin for their understanding and patience while I took the time to work on this book.

If it were not for their support of my original Linux development efforts, I would not be able to do this book at all. Thanks also to Alessandro and Jon for offering to let me work on this book; I am honored that they let me participate in it. Much gratitude is given to all of the Linux kernel sintle, who were unselfish enough to write code in the public view, so that I and others could learn so much from just reading lldd3.

Also, for everyone who has ever sent me bug reports, critiqued my code, and flamed me for doing stupid things, you have all taught me so much about how to be a better programmer and, throughout it all, made me feel very welcome to be part of this community. The publication of this edition coincides with my twelth year of working with Linux and, shockingly, my twenty-fifth year in the computing field. Computing seemed like a fast-moving field back inbut things have sped up a lot since then.

Keeping Linux Device Drivers up to date is increasingly a challenge; the Linux kernel hackers continue to improve their code, and they have little patience for documentation that fails to keep up.

Linux continues to succeed in the market and, more importantly, in the hearts and minds of developers worldwide.

The success of Linux is clearly a testament to its technical quality and to the numerous benefits of free software in general. But the true key to its success, in my opinion, lies in the fact that it has brought the fun back to computing. With Linux, anybody can get their hands into the system and play in a sandbox where contributions from any direction are welcome, but where technical excellence is valued above all else.

Linux not only provides us with a top-quality operating system; it gives us the opportunity to be part of its future development and to have fun while we’re at it.

In my 25 years in the field, I have had many interesting opportunities, from programming the first Cray computers in Fortran, on punch cards to seeing the minicomputer and Unix workstation waves, through to the current, microprocessor-dominated era. Never, though, have I seen the field more full of life, opportunity, and fun. Never have we had such control over our own tools and their evolution. Linux, and free software in general, is clearly the driving force behind those changes.

My hope is that this edition helps to bring that fun and opportunity to a new set of Linux developers. Whether your interests are in the kernel or in user space, I hope you find this book to be a useful and interesting guide to just how the kernel works with the hardware. I hope it helps and inspires you to fire up your editor and slngle make our shared, free operating system even better.

Linux has come a long way, but it is also just beginning; it will be more than interesting to ldf3 participate in—what happens from here. I’ve always enjoyed computers because they can talk to external hardware. Back then, the community was a small one, and there wasn’t much documentation about writing drivers around, so I started writing for Linux Journal. That’s how things started: The computing world is different now: I hope this book furthers two aims: That’s why, after the first edition proved interesting to the public, the snigle authors of the second edition switched to a free license, supported lxd3 our editor and our publisher.


I’m betting this is the right approach to information, and it’s great singlee team up with other people sharing this vision. I’m excited by what I witness in the embedded arena, and I hope this text helps by doing more; but ideas are moving fast these days, and it’s already time to plan for the fourth edition, and look for a fourth author to help.

It seems like a long time ago that I picked up the first edition of this Linux Device Drivers book in order to figure out how to write a real Linux driver. That first edition was a great guide to helping me understand the internals of this operating system that I had already been using for a number of years but whose kernel had never taken the time to look into. With the knowledge gained from that book, and by reading other programmers’ code already present in the kernel, my first horribly buggy, broken, and very SMP-unsafe driver was accepted by the kernel community into the main kernel tree.

Despite receiving my first bug report five minutes later, I was hooked on wanting to do as much as I could to make ldd3 operating system the best it could possibly be. I am honored that I’ve had the ability to contribute to this book. I hope that it enables others to learn the details about the kernel, discover that driver development is not a scary or forbidding place, and possibly encourage others to join in and help in the collective effort of making this operating system work on every computing platform with every type of device available.

The development procedure is fun, the community is rewarding, and everyone benefits from the effort involved.

LDD3 Project Setup

Now it’s back to making this edition obsolete by fixing current bugs, changing APIs to work better and be simpler to understand for everyone, and adding new features. Come along; we can always use the help. This book should be an interesting source of information both for people who want to experiment with their computer and for technical programmers who face the need to deal with the inner levels of a Linux box.

Note that “a Linux box” is a wider concept than “a PC running Linux,” as many platforms are supported by our operating system, and kernel programming is by no means bound to a specific platform. We hope this book is useful as a starting point for people who want to become kernel hackers but don’t know where to start.

On the technical side, this text should offer a hands-on approach to understanding the kernel internals and some of the design choices made by the Linux developers.

Although the main, official target of the book is teaching how to write device drivers, the material should give an interesting overview of the kernel implementation as well. Although real hackers can find all the necessary information in the official kernel sources, usually a written text can be helpful in developing programming skills.

The text you are approaching is the result of hours of patient grepping through the kernel sources, and we hope the final result is worth the effort it took. The Linux enthusiast should find in this book enough food for her mind to start playing with the code base and should be able to join singel group of developers that is continuously working on new capabilities and performance enhancements.

This book does not cover the Linux kernel in its entirety, of course, but Linux device driver authors need to know how to work with many of the kernel’s subsystems. Therefore, it makes a good introduction to kernel sinfle in general. Linux is still a work in progress, and there’s always a place for new programmers to jump into the game. If, on the other hand, you are just trying to write a device driver for your own device, and you don’t want to muck with the kernel internals, the text should be modularized enough to fit your needs as well.

If you don’t want to go deep into the details, you can just skip the most technical sections, and stick to the standard API used by device drivers to seamlessly integrate with the rest of the kernel. The book introduces its topics in ascending order of complexity and is divided into two parts. The first part Chapters begins with the proper setup ld3 kernel modules and goes on to describe the various aspects of programming that you’ll need in order to write a full-featured driver for a char-oriented device.