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


All the preceding APIs and helpers work on all hardware interrupts except for the non-maskable interrupt (NMI)The NMI is an arch-specific interrupt and is used to implement stuff such as hardware watchdogs and debug features (for example, an unconditional kernel stack dump for all cores; we'll show an example of this very shortly). Also, NMI interrupt lines cannot be shared.

A quick example of exploiting the NMI can be shown with the kernel's so-called magic SysRq facility. To see the keyboard hotkeys that are assigned for magic SysRq, you must invoke or trigger it by typing in the [Alt][SysRq][letter] key combination. 

magic SysRq triggering: Instead of getting your fingers all twisted typing [Alt][SysRq][letter], there's an easier – and more importantly non-interactive – way to do so: just echo the relevant letter to a proc pseudofile (as root, of course): echo letter/proc/sysrq-trigger.