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)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

Our simple work queue kernel module code view

Let's get hands-on with a work queue! In the following sections, we will write a simple demo kernel module (ch5/workq_simple) that demonstrates using the kernel-default workqueue to execute a work task. It's actually built upon our earlier LKM, which we used to demonstrate kernel timers (ch5/timer_simple). Let's check it out code-wise (as usual, we won't show the full code here, only the most relevant portions). We'll begin by looking at its private context data structure and init method:

static struct st_ctx {
struct work_struct work;
struct timer_list tmr;
int data;
} ctx;
[ ... ]
static int __init workq_simple_init(void)
{
ctx.data = INITIAL_VALUE;
/* Initialize our work queue */
INIT_WORK(&ctx.work, work_func);
/* Initialize our kernel timer */
ctx.tmr.expires = jiffies + msecs_to_jiffies(exp_ms);
ctx.tmr.flags = 0;
timer_setup(&ctx.tmr, ding, 0);
...