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

The downfall case

Let's make it interesting now by not using a convenient rounded power-of-2 size as the requirement. This time, let's say that the device driver requests a memory chunk of size 132 KB. What will the buddy system allocator do? As, of course, it cannot allocate less memory than requested, it allocates more – you guessed it (see Figure 8.2), the next available memory chunk is on order 7, of size 256 KB. But the consumer (the driver) is only going to see and use the first 132 KB of the 256 KB chunk allocated to it. The remaining (124 KB) is wasted (think about it, that's close to 50% wastage!). This is called internal fragmentation (or wastage) and is the critical failing of the binary buddy system!

You will learn, though, that there is indeed a mitigation to this: a patch was contributed to deal with similar scenarios (via the alloc_pages_exact() / free_pages_exact() APIs). We will cover the APIs to...