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

Dealing with the GFP flags

You will notice that the first parameter to all the previous allocator APIs (or macros) is gfp_t gfp_mask. What does this mean? Essentially, these are GFP flags. These are flags (there are several of them) used by the kernel's internal memory management code layers. For all practical purposes, for the typical kernel module (or device driver) developer, just two GFP flags are crucial (as mentioned before, the rest are for internal usage). They are as follows:

  • GFP_KERNEL
  • GFP_ATOMIC

Deciding which of these to use when performing memory allocation via the page allocator APIs is important; a key rule to always remember is the following: 

If in process context and it is safe to sleep, use the GFP_KERNEL flag. If it is unsafe to sleep (typically, when in any type of atomic or interrupt context), you must use the GFP_ATOMIC flag.

Following the preceding rule is critical...