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

The purpose behind the proc filesystem

The purpose behind the proc filesystem is two-fold:

  • One, it is a simple interface for developers, system administrators, and anyone really to look deep inside the kernel so that they can gain information regarding the internals of processes, the kernel, and even hardware. Using this interface only requires you to know basic shell commands such as cd, cat, echo, ls, and so on.
  • Two, as the root user and, at times, the owner, you can write into certain pseudo files under /proc/sys, thus tuning various kernel parameters. This feature is called sysctl. As an example, you can tune various IPv4 networking parameters in /proc/sys/net/ipv4/. They are all documented here:

Changing the value of a proc-based tunable is easy; for example, let's change the maximum number of threads allowed at any given point in time on the box. Run the following commands as root:

# cat /proc/sys...