The Linux Programming Interface

1424 Appendix E

z http://www.kernelnewbies.org/, Linux Kernel Newbies, is a starting point for pro-

grammers who want to learn about and modify the Linux kernel.

z http://lxr.linux.no/linux/, Linux Cross-reference, provides browser access to vari-

ous versions of the Linux kernel source code. Each identifier in a source file is

hyperlinked to make it easy to find the definition and uses of that identifier.

The kernel source code

If none of the preceding sources answer our questions, or if we want to confirm that

documented information is true, then we can read the kernel source code. Although

parts of the source code can be difficult to understand, reading the code of a particu-

lar system call in the Linux kernel source (or a library function in the GNU C library

source) can often prove to be a surprisingly quick way to find the answer to a question.

If the Linux kernel source code has been installed on the system, it can usually

be found in the directory /usr/src/linux. Table E-1 provides summary information

about some of the subdirectories under this directory.

Table E-1: Subdirectories in the Linux kernel source tree

Directory Contents

Documentation Documentation of various aspects of the kernel

arch Architecture-specific code, organized into subdirectories—for example,

alpha, arm, ia64, sparc, and x86

drivers Code for device drivers

fs File system–specific code, organized into subdirectories—for example,

btrfs, ext4, proc (the /proc file system), and vfat

include Header files needed by kernel code

init Initialization code for the kernel

ipc Code for System V IPC and POSIX message queues

kernel Code related to processes, program execution, kernel modules, signals,

time, and timers

lib General-purpose functions used by various parts of the kernel

mm Memory-management code

net Networking code (TCP/IP, UNIX and Internet domain sockets)

scripts Scripts to configure and build the kernel