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

Rate limiting the printk instances

When we emit printk instances from a code path that is executed very often, the sheer amount of printk instances might quickly overflow the kernel log buffer (in RAM; remember that it's a circular buffer), thus overwriting what might well be key information. Besides that, ever-growing non-volatile log files that then repeat pretty much the same printk instances (almost) ad infinitum are not a great idea either and waste disk space, or worse, flash space. For example, think of a large-ish printk in an interrupt handler code path. What if the hardware interrupt is invoked at a frequency of, say, 100 Hz, that is, 100 times every single second!

To mitigate these issues, the kernel provides an interesting alternative: the rate-limited printk. The printk_ratelimited() macro has identical syntax to the regular printk; the key point is that it effectively suppresses regular prints when certain conditions...