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

Linux Trace Toolkit next generation

A superb tool for tracing and profiling is the powerful Linux Tracing Toolkit next generation (LTTng) toolset, a Linux Foundation project. LTTng allows you to trace both userspace (applications) and/or the kernel code paths in minute detail. This can tremendously aid you in understanding where performance bottlenecks occur, as well as aiding you in understanding the overall code flow and thus in learning about how the code actually performs its tasks.

In order to learn how to install and use it, I refer you to its very good documentation here: https://lttng.org/docs​ (try https://lttng.org/download/ for installation for common Linux distributions). It is also highly recommended that you install the Trace Compass GUI: https://www.eclipse.org/tracecompass/. It provides an excellent GUI for examining and interpreting LTTng's output.

Trace Compass minimally requires a Java Runtime Environment (JRE) to be installed as well. I installed one on my Ubuntu 20.04 LTS system with sudo apt install openjdk-14-jre.

As an example (I can't resist!), here's a screenshot of a capture by LTTng being "visualized" by the superb Trace Compass GUI. Here, I show a couple of hardware interrupts (IRQ lines 1 and 130, the interrupt lines for the i8042 and Wi-Fi chipset, respectively, on my native x86_64 system.):

Figure 1.9 – Sample screenshot of the Trace Compass GUI; samples recorded by LTTng showing IRQ lines 1 and 130

The pink color in the upper part of the preceding screenshot represents the occurrence of a hardware interrupt. Underneath that, in the IRQ vs Time tab (it's only partially visible), the interrupt distribution is seen. (In the distribution graph, the y axis is the time taken; interestingly, the network interrupt handler – in red – seems to take very little time, the i8042 keyboard/mouse controller chip's handler – in blue – takes more time, even exceeding 200 microseconds!)