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 secret driver – cleanup

It's important to realize that we must free any buffers we have allocated. Here, however, as we performed a managed allocation in the init code (devm_kzalloc()), we have the benefit of not needing to worry about cleanup; the kernel handles it. Of course, in the driver's cleanup code path (invoked upon rmmod(8)), we deregister the misc driver with the kernel:

static void __exit miscdrv_rdwr_exit(void)
{
misc_deregister(&llkd_miscdev);
pr_info("LLKD misc (rdwr) driver deregistered, bye\n");
}

You will notice that we also, seemingly uselessly, use two global integers, ga and gbin places in this version of the driver. Indeed, they have no real meaning here; the reason we have them at all becomes clear only in the last two chapters of this book, on kernel synchronization. Please ignore them for now.

On this note, you'll perhaps realize that the way we have arbitrarily accessed global data in this driver can cause concurrency issue (data races!); yes indeed; we shall set aside the deep and crucial coverage of kernel concurrency and synchronization to the book's last two chapters.