Organization of Material

This book is divided into three parts, each of which provides the reader with knowledge necessary to succeed in the study of Linux internals.

Part I provides the necessary tools and understanding to tackle the exploration of the kernel internals:

Chapter 1, "Overview," provides a history of Linux and UNIX, a listing of the many distributions, and a short overview of the various kernel subsystems from a user space perspective.

Chapter 2, "Exploration Toolkit," provides a description of the data structures and language usage commonly found throughout the Linux kernel, an introduction to assembly for x86 and PowerPC architectures, and a summary of tools and utilities used to get the information needed to understand kernel internals.

Part II introduces the reader to the basic concepts in each kernel subsystem and to trace the code that executes the subsystem functionality:

Chapter 3, "Processes: The Principal Model of Execution," covers the implementation of the process model. We explain how processes come to be and discuss the flow of control of a user space process into kernel space and back. We also discuss how processes are implemented in the kernel and discuss all data structures associated with process execution. This chapter also covers interrupts and exceptions, how these hardware mechanisms occur in each of the architectures, and how they interact with the Linux kernel.

Chapter 4, "Memory Management," describes how the Linux kernel tracks and manages available memory among various user space processes and the kernel. This chapter describes the way in which the kernel categorizes memory and how it decides to allocate and deallocate memory. It also describes in detail the mechanism of the page fault and how it is executed in the hardware.

Chapter 5, "Input/Output," describes how the processor interacts with other devices, and how the kernel interfaces and controls these interactions. This chapter also covers various kinds of devices and their implementation in the kernel.

Chapter 6, "Filesystems," provides an overview of how files and directories are implemented in the kernel. This chapter introduces the virtual filesystem, the layer of abstraction used to support multiple filesystems. This chapter also traces the execution of file-related operations such as open and close.

Chapter 7, "Scheduling and Kernel Synchronization," describes the operation of the scheduler, which allows multiple processes to run as though they are the only process in the system. This chapter covers in detail how the kernel selects which task to execute and how it interfaces with the hardware to switch from one process to another. This chapter also describes what kernel preemption is and how it is executed. Finally, it describes how the system clock works and its use by the kernel to keep time.

Chapter 8, "Booting the Kernel," describes what happens from Power On to Power Off. It traces how the various processors handle the loading of the kernel, including a description of BIOS, Open Firmware, and bootloaders. This chapter then goes through the linear order in kernel bringup and initialization, covering all the subsystems discussed in previous chapters.

Part III deals with a more hands-on approach to building and interacting with the Linux kernel:

Chapter 9, "Building the Linux Kernel," covers the toolchain necessary to build the kernel and the format of the object files executed. It also describes in detail how the Kernel Source Build system operates and how to add configuration options into the kernel build system.

Chapter 10, "Adding Your Code to the Kernel," describes the operation of /dev/random, which is seen in all Linux systems. As it traces the device, the chapter touches on previously described concepts from a more practical perspective. It then covers how to implement your own device in the kernel.