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)
Section 1: The Basics
Writing Your First Kernel Module - LKMs Part 2
Section 2: Understanding and Working with the Kernel
Kernel Memory Allocation for Module Authors - Part 1
Kernel Memory Allocation for Module Authors - Part 2
Section 3: Delving Deeper
About Packt

A more complex case

Now, let's say that, unlike the previous simple case, when the device driver requests 128 KB, the order 5 list is null; thus, as per the page allocator algorithm, we go to the list on the next order, 6, and check it. Let's say it's non-null; the algorithm now dequeues a 256 KB chunk and splits (or cuts) it in half. Now, one half (of size 128 KB) goes to the requester, and the remaining half (again, of size 128 KB) is enqueued on to the order 5 list.

The really interesting property of the buddy system is what happens when the requester (the device driver), at some later point in time, frees the memory chunk. As expected, the algorithm calculates (via its order) that the just-freed chunk belongs on the order 5 list. But before blindly enqueuing it there, it looks for its buddy block, and in this case, it (possibly) finds it! It now merges the two buddy blocks into a single larger block (of...