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 newer refcount_t versus older atomic_t interfaces

At the outset of this topic area, it's important to mention this: from the 4.11 kernel, there is a newer and better set of interfaces christened the refcount_t APIs, meant for a kernel space object's reference counters. It greatly improves the security posture of the kernel (via much-improved Integer OverFlow (IoF) and Use After Free (UAF) protection as well as memory ordering guarantees, which the older atomic_t APIs lack). The refcount_t interfaces, like several other security technologies used on Linux, have their origins in work done by The PaX Team – (it was called PAX_REFCOUNT).

Having said that, the reality is that (as of the time of writing) the older atomic_t interfaces are still very much in use within the kernel core and drivers (they are slowly being converted, with the older atomic_t interfaces being moved to the newer refcount_t model and...