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

Our simple kernel timer module code view 1

Without further ado, let's dive into the code of a simple kernel timer, written using the Loadable Kernel Module (LKM) framework (this can be found at ch5/timer_simple). As with most drivers, we keep a context or private data structure containing the information required while running; here, we call it st_ctx. We instantiate it as the ctx variable. We also specify the time to expire (as 420 ms) in a global named exp_ms:

// ch5/timer_simple/timer_simple.c
#include <linux/timer.h>
[ ... ]
static struct st_ctx {
struct timer_list tmr;
int data;
} ctx;
static unsigned long exp_ms = 420;

Now, let's check out the first portion of our init code:

static int __init timer_simple_init(void)

/* Initialize our kernel timer */
ctx.tmr.expires = jiffies + msecs_to_jiffies(exp_ms);
ctx.tmr.flags = 0;
timer_setup(&ctx.tmr, ding, 0);

This is pretty straightforward. First...