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

Using the reader-writer spinlock

Visualize a piece of kernel (or driver) code wherein a large, global, doubly linked circular list (with a few thousand nodes) is being searched. Now, since the data structure is global (shared and writable), accessing it constitutes a critical section that requires protection.

Assuming a scenario where searching the list is a non-blocking operation, you'd typically use a spinlock to protect the critical section. A naive approach might propose not using a lock at all since we're only reading data within the list, not updating it. But, of course (as you have learned), even a read on shared writable data has to be protected to protect against an inadvertent write occurring simultaneously, thus resulting in a dirty or torn read.

So, we conclude that we require the spinlock; we imagine the pseudocode might look something like this:

for (p = &listhead; (p = next_node(p)) != &listhead; ) {