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

The mutex trylock variant

What if you would like to implement a busy-wait semantic; that is, test for the availability of the (mutex) lock and, if available (meaning it's currently unlocked), acquire/lock it and continue with the critical section code path? If this is not available (it's currently in the locked state), do not wait for the lock; instead, perform some other work and retry. In effect, this is a non-blocking mutex lock variant and is called the trylock; the following flowchart shows how it works:

Figure 12.8 – The "busy wait" semantic, a non-blocking trylock operation

The API for this trylock variant of the mutex lock is as follows:

int mutex_trylock(struct mutex *lock);

This API's return value signifies what transpired at runtime:

  • A return value of 1 indicates that the lock has been successfully acquired.
  • A return value of 0 indicates that the lock is currently contended (locked).
Though it might sound...