Book Image

Linux Kernel Programming

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Programming

By: Kaiwan N. Billimoria

Overview of this book

Linux Kernel Programming is a comprehensive introduction for those new to Linux kernel and module development. This easy-to-follow guide will have you up and running with writing kernel code in next-to-no time. This book uses the latest 5.4 Long-Term Support (LTS) Linux kernel, which will be maintained from November 2019 through to December 2025. By working with the 5.4 LTS kernel throughout the book, you can be confident that your knowledge will continue to be valid for years to come. You’ll start the journey by learning how to build the kernel from the source. Next, you’ll write your first kernel module using the powerful Loadable Kernel Module (LKM) framework. The following chapters will cover key kernel internals topics including Linux kernel architecture, memory management, and CPU scheduling. During the course of this book, you’ll delve into the fairly complex topic of concurrency within the kernel, understand the issues it can cause, and learn how they can be addressed with various locking technologies (mutexes, spinlocks, atomic, and refcount operators). You’ll also benefit from more advanced material on cache effects, a primer on lock-free techniques within the kernel, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this kernel book, you’ll have a detailed understanding of the fundamentals of writing Linux kernel module code for real-world projects and products.
Table of Contents (19 chapters)
1
Section 1: The Basics
6
Writing Your First Kernel Module - LKMs Part 2
7
Section 2: Understanding and Working with the Kernel
10
Kernel Memory Allocation for Module Authors - Part 1
11
Kernel Memory Allocation for Module Authors - Part 2
14
Section 3: Delving Deeper
17
About Packt

Iterating over the task list I – displaying all processes

The kernel provides a convenient routine, the for_each_process() macro, which lets you easily iterate over every process in the task list:

// include/linux/sched/signal.h:
#define for_each_process(p) \
for (p = &init_task ; (p = next_task(p)) != &init_task ; )

Clearly, the macro expands to a for loop, allowing us to loop over the circular list. init_task is a convenient 'head' or starting pointer – it points to the task structure of the very first user space process, traditionally init(1), now systemd(1).

Note that the for_each_process() macro is expressly designed to only iterate over the main() thread of every process and not the ('child' or peer) threads.

A brief snippet of our ch6/foreach/prcs_showall kernel module's output is shown here (when run on our x86_64 Ubuntu 18.04 LTS guest system...