Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By : Kaiwan N Billimoria
Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By: Kaiwan N Billimoria

Overview of this book

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization is an ideal companion guide to the Linux Kernel Programming book. This book provides a comprehensive introduction for those new to Linux device driver development and will have you up and running with writing misc class character device driver code (on the 5.4 LTS Linux kernel) in next to no time. You'll begin by learning how to write a simple and complete misc class character driver before interfacing your driver with user-mode processes via procfs, sysfs, debugfs, netlink sockets, and ioctl. You'll then find out how to work with hardware I/O memory. The book covers working with hardware interrupts in depth and helps you understand interrupt request (IRQ) allocation, threaded IRQ handlers, tasklets, and softirqs. You'll also explore the practical usage of useful kernel mechanisms, setting up delays, timers, kernel threads, and workqueues. Finally, you'll discover how to deal with the complexity of kernel synchronization with locking technologies (mutexes, spinlocks, and atomic/refcount operators), including more advanced topics such as cache effects, a primer on lock-free techniques, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this Linux kernel book, you'll have learned the fundamentals of writing Linux character device driver code for real-world projects and products.
Table of Contents (11 chapters)
Section 1: Character Device Driver Basics
User-Kernel Communication Pathways
Handling Hardware Interrupts
Working with Kernel Timers, Threads, and Workqueues
Section 2: Delving Deeper

Per-CPU – an example kernel module

A hands-on session with our sample per-CPU demo kernel module will definitely help in using this powerful feature (code here: ch13/2_percpu). Here, we define and use two per-CPU variables:

  • A statically allocated and initialized per-CPU integer
  • A dynamically allocated per-CPU data structure

As an interesting way to help demo per-CPU variables, let's do this: we shall arrange for our demo kernel module to spawn off a couple of kernel threads. Let's call them thrd_0 and thrd_1. Furthermore, once created, we shall make use of the CPU mask (and API) to affine our thrd_0 kernel thread on CPU 0 and our thrd_1 kernel thread on CPU 1 (hence, they will be scheduled to run on only these cores; of course, we must test this code on a VM with at least two CPU cores).

The following code snippets illustrate how we define and use the per-CPU variables (we leave out the code that creates the kernel...