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)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

Using the atomic_t and refcount_t interfaces

In our simple demo misc character device driver program's (miscdrv_rdwr/miscdrv_rdwr.c) open method (and elsewhere), we defined and manipulated two static global integers, ga and gb:

static int ga, gb = 1;
[...]
ga++; gb--;

By now, it should be obvious to you that this – the place where we operate on these integers – is a potential bug if left as is: it's shared writable data (in a shared state) and therefore a critical section, thus requiring protection against concurrent access. You get it; so, we progressively improved upon this. In the previous chapter, understanding the issue, in our ch12/1_miscdrv_rdwr_mutexlock/1_miscdrv_rdwr_mutexlock.c program, we first used a mutex lock to protect the critical section. Later, you learned that using a spinlock to protect non-blocking critical sections such as this one would be (far) superior to using a mutex in terms of performance; so, in our next driver,...