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

Variations of scheduling your work task

There are a few variations of the schedule_work() API we just described, all of which are available via the schedule[_delayed]_work[_on]() APIs. Let's briefly enumerate them. First, let's look at the schedule_delayed_work() inline function, whose signature is as follows:

bool schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);

Use this routine when you want to delay the execution of the workqueue handler function by a specified amount of time; the second parameter, delay, is the number of jiffies you want to wait for. Now, we know that the jiffies variable increments by HZ jiffies per second; thus, to have your work task delayed by n seconds, specify n * jiffies. Similarly, you could always pass the msecs_to_jiffies(n) value as the second parameter to have it execute n milliseconds from now.

Next, notice that the first parameter to schedule_delayed_work() is different; it&apos...