Understanding the Linux Kernel, Second Edition

Appendix C. Source Code Structure

To help you to find your way through the files of the source code, we briefly describe the organization of the kernel directory tree. As usual, all pathnames refer to the main directory of the Linux kernel, which is, in most Linux distributions, /usr/src/linux.

Linux source code for all supported architectures is contained in about 8750 C and Assembly files stored in about 530 subdirectories; it consists of about 4 million lines of code, which occupy more than 144 megabytes of disk space.

The following list illustrates the directory tree containing the Linux source code. Please notice that only the subdirectories somehow related to the target of this book have been expanded.

Directory	Description
Documentation	Text files with general explanations and hints about kernel components
arch	Platform-dependent code
→ i386	IBM’s PC architecture
→ kernel	Kernel core
→ mm	Memory management
→ math-emu	Software emulator for floating-point unit
→ lib	Hardware-dependent utility functions
→ boot	Bootstrapping
→ compressed	Compressed kernel handling
→ tools	Programs to build compressed kernel image
→ alpha	Hewlett-Packard’s Alpha architecture
→ arm	Architectures based on ARM processors
→ cris	Axis Communication AB’s Code Reduced Instruction Set architecture used by thin-servers
→ ia64	Workstations based on Intel’s 64-bit Itanium microprocessor
→ m68k	Motorola’s MC680x0-based architecture
→ mips	MIPS architecture ...