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

Understanding what a netlink socket is

So, what is a netlink socket? We shall keep it simple a netlink socket is a "special" socket family that exists only on the Linux OS since version 2.2. Using it, you can set up Inter-Process Communication (IPC) between a user mode process (or thread) and a component within the kernel; in our case, a kernel module, which is typically a driver.

It is similar to a UNIX domain datagram socket in many ways; it's meant for communication on the localhost only and not across systems. While UNIX domain sockets use a pathname as their namespace (a special "socket" file), netlink sockets use a PID. Pedantically, this is a port ID and not a process ID, although realistically, process IDs are very often used as the namespace. The modern kernel core (besides drivers) uses netlink sockets in many cases – as one example, the iproute2 networking utilities use it to configure wireless drivers. As another interesting...