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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 kernel's 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 how its developers set about doing it.

This, the starting point of understanding, is what the written word serves best.

Robert Love's contribution provides a means by which experienced developers can gain that essential view of what services the kernel subsystems are supposed to provide, and 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 kernel's 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 that merely reading the code does not provide. The serious kernel developer will join the development mailing lists and will interact with other developers. This 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 Robert's 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.

Andrew Morton
Open Source Development Labs

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