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

Setting up and using kernel timers

A timer provides software with a means of being asynchronously notified when a designated amount of time has passed. All kinds of software, both in user and kernel space, require timers; this commonly includes network protocol implementations, block layer code, device drivers, and various kernel subsystems. This timer provides a means of asynchronous notification, thus allowing the driver to execute work in parallel with the running timer. An important question that arises is, how will I know when the timer expires? In user space apps, typically, the kernel sends a signal to the relevant process (the signal is typically SIGALRM).

In kernel space, it's a bit nuanced. As you will know from our discussion on top and bottom halves for hardware interrupts (see Chapter 4, Handling Hardware Interrupts, the Understanding and using top and bottom halves section), after the timer interrupt's top half (or ISR) completes, the kernel will ensure...