Linux Kernel Programming

Kaiwan N Billimoria

• Publisher: Packt Publishing
• Year: 2021
• ISBN:
  9781789955927
• Topic: Computer Science
• Subtopic: Operating Systems
• Index: Computer Science

Learn how to write high-quality kernel module code, solve common Linux kernel programming issues, and understand the fundamentals of Linux kernel internals

Key Features

• Discover how to write kernel code using the Loadable Kernel Module framework
• Explore industry-grade techniques to perform efficient memory allocation and data synchronization within the kernel
• Understand the essentials of key internals topics such as kernel architecture, memory management, CPU scheduling, and kernel synchronization

Book Description

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.

What you will learn

• Write high-quality modular kernel code (LKM framework) for 5.x kernels
• Configure and build a kernel from source
• Explore the Linux kernel architecture
• Get to grips with key internals regarding memory management within the kernel
• Understand and work with various dynamic kernel memory alloc/dealloc APIs
• Discover key internals aspects regarding CPU scheduling within the kernel
• Gain an understanding of kernel concurrency issues
• Find out how to work with key kernel synchronization primitives

Who this book is for

This book is for Linux programmers beginning to find their way with Linux kernel development. If you're a Linux kernel and driver developer looking to overcome frequent and common kernel development issues, or understand kernel intervals, you'll find plenty of useful information.You'll need a solid foundation of Linux CLI and C programming before you can jump in.

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Section 1: The Basics

Here, you will learn how to perform basic kernel development tasks. You will set up a kernel development workspace, build a Linux kernel from source, learn about the LKM framework, and write a "Hello, world" kernel module.

This section comprises the following chapters:

• Chapter 1, Kernel Workspace Setup
• Chapter 2, Building the 5.x Linux Kernel from Source, Part 1
• Chapter 3, Building the 5.x Linux Kernel from Source, Part 2
• Chapter 4, Writing Your First Kernel Module – LKMs Part 1
• Chapter 5, Writing Your First Kernel Module – LKMs Part 2

We highly recommend you also make use of this book's companion guide, Linux Kernel Programming (Part 2).

It's an excellent industry-aligned beginner's guide to writing misc character drivers, performing I/O on peripheral chip memory and handling hardware interrupts. This book is primarily for Linux programmers beginning to find their way with device driver development. Linux device driver developers looking to overcome frequent and common kernel/driver development issues, as well as understand and learn to perform common driver tasks - the modern Linux Device Model (LDM) framework, user-kernel interfaces, performing peripheral I/O, handling hardware interrupts, dealing with concurrency and more - will benefit from this book. A basic understanding of Linux kernel internals (and common APIs), kernel module development and C programming is required.

You can get this book for free along with your copy, alternately you can also find this eBook in the GitHub repository: https://github.com/PacktPublishing/Linux-Kernel-Programming/tree/master/Linux-Kernel-Programming-(Part-2).

Kernel Workspace Setup

Hello, and welcome to this book on learning Linux kernel development. To get the most out of this book, it is very important that you first set up the workspace environment that we will be using throughout the book. This chapter will teach you exactly how to do this and get started.

We will install a recent Linux distribution, preferably as a Virtual Machine (VM), and set it up to include all the required software packages. We will also clone this book's code repository on GitHub, and learn about a few useful projects that will help along this journey.

The best way to learn something is to do so empirically – not taking anyone's word on anything at all, but trying it out and experiencing it for yourself. Hence, this book gives you many hands-on experiments and kernel code examples that you can and indeed must try out yourself; this will greatly aid in your making real progress and deeply learning and understanding various aspects of Linux kernel and driver development. So, let's begin!

This chapter will take us through the following topics, which will help us set up our environment:

• Running Linux as a guest VM
• Setting up the software – distribution and packages
• A few additional useful projects

Technical requirements

You will need a modern desktop PC or laptop. Ubuntu Desktop specifies the following as "recommended system requirements" for the installation and usage of the distribution:

• A 2 GHz dual core processor or better.
• RAM:
  • Running on physical host: 2 GB or more system memory (more will certainly help).
  • Running as a guest VM: The host system should have at least 4 GB RAM (the more the better and the smoother the experience).
• 25 GB of free hard drive space (I suggest more, at least double this).
• Either a DVD drive or a USB port for the installer media (not required when setting up Ubuntu as a guest VM).
• Internet access is definitely helpful and required at times.

As performing tasks such as building a Linux kernel from source is a very memory- and CPU-intensive process, I highly recommend that you try it out on a powerful Linux system with plenty of RAM and disk space to spare as well. It should be pretty obvious – the more RAM and CPU power the host system has, the better!

Like any seasoned kernel contributor, I would say that working on a native Linux system is best. However, for the purposes of this book, we cannot assume that you will always have a dedicated native Linux box available to you. So, we will assume that you are working on a Linux guest. Working within a guest VM also adds an additional layer of isolation and thus safety.

Cloning our code repository: The complete source code for this book is freely available on GitHub at https://github.com/PacktPublishing/Linux-Kernel-Programming. You can clone and work on it by cloning the git tree, like so:

git clone https://github.com/PacktPublishing/Linux-Kernel-Programming.git

The source code is organized chapter-wise. Each chapter is represented as a directory – for example, ch1/ has the source code for this chapter. The root of the source tree has some code that is common to all chapters, such as the source files convenient.h, klib_llkd.c, as well as others.

For efficient code browsing, I would strongly recommend that you always index the code base with ctags(1) and/or cscope(1). For example, to set up the ctags index, just cd to the root of the source tree and type ctags -R .

Unless noted otherwise, the code output we show in the book is the output as seen on an x86-64 Ubuntu 18.04.3 LTS guest VM (running under Oracle VirtualBox 6.1). You should realize that due to (usually minor) distribution – and even within the same distributions but differing versions – differences, the output shown here may not perfectly match what you see on your Linux system.

Running Linux as a guest VM

As discussed previously, a practical and convenient alternative to using a native Linux system is to install and use the Linux distribution as a guest OS on a VM. It's key that you install a recent Linux distribution, preferably as a VM to be safe and avoid unpleasant data loss or other surprises. The fact is when working at the level of the kernel, abruptly crashing the system (and the data loss risks that arise thereof) is actually a commonplace occurrence. I recommend using Oracle VirtualBox 6.x (or the latest stable version) or other virtualization software, such as VMware Workstation.

Both of these are freely available. It's just that the code for this book has been tested on VirtualBox 6.1. Oracle VirtualBox is considered Open Source Software (OSS) and is licensed under the GPL v2 (the same as the Linux kernel). You can download it from https://www.virtualbox.org/wiki/Downloads. Its documentation can be found here: https://www.virtualbox.org/wiki/End-user_documentation.

The host system should be either MS Windows 10 or later (of course, even Windows 7 will work), a recent Linux distribution (for example, Ubuntu or Fedora), or macOS. So, let's get started by installing our Linux guest.

Installing a 64-bit Linux guest

Here, I won't delve into the minutiae of installing Linux as a guest on Oracle VirtualBox, the reason being that this installation is not directly related to Linux kernel development. There are many ways to set up a Linux VM; we really don't want to get into the details and the pros and cons of each of them here.

But if you are not familiar with this, don't worry. For your convenie...