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

Interfacing via the debug filesystem (debugfs)

Imagine for a moment, the quandary faced by you, a driver developer, on Linux: you want to implement an easy yet elegant way to provide debug "hooks" from your driver to the user space. For example, the user simply performing a cat(1) on a (pseudo) file should result in your driver's "debug callback" function being invoked. It will then proceed to dump some status information (perhaps a "driver context" structure) to the user mode process, which will faithfully dump it to stdout.

Okay, no problem: in the days before the 2.6 release, we could (as you learned in the Interfacing via the proc filesystem (procfs) section) happily use the procfs layer to interface our driver with the user space. Then, from 2.6 Linux onward, the kernel community vetoed this approach. We were told to strictly stop using procfs and instead use the sysfs layer as the means to interface our drivers with the user space. However...