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

Writing a kernel module to use the basic slab APIs

In the following code snippet, take a look at the demo kernel module code (found at ch8/slab1/). In the init code, we merely perform a couple of slab layer allocations (via the kmalloc() and kzalloc() APIs), print some information, and free the buffers in the cleanup code path (of course, the full source code is accessible at this book's GitHub repository). Let's look at the relevant parts of the code step by step.

At the start of the init code of this kernel module, we initialize a global pointer (gkptr) by allocating 1,024 bytes to it (remember: pointers have no memory!) via the kmalloc() slab allocation API. Notice that, as we're certainly running in process context here, and it is thus "safe to sleep," we use the GFP_KERNEL flag for the second parameter (just in case you want to refer back, the earlier section, The GFP flags – digging deeper, has it...