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

Test sleep in an atomic context

You have already learned that the one thing we should not do is sleep (block) in any kind of atomic or interrupt context. Let's put this to the test. As always, the empirical approach where you test things for yourself rather than relying on other's experiences is key!

How exactly can we test this? Easy: we shall use a simple integer module parameter, buggy, that, when set to 1 (the default value being 0), executes a code path within our spinlock's critical section that violates this rule. We shall invoke the schedule_timeout() API (which, as you learned in Chapter 5Working with Kernel Timers, Threads, and Workqueues, in the Understanding how to use the *sleep() blocking APIs section) internally invokes schedule(); it's how we go to sleep in the kernel space). Here's the relevant code:

// ch12/2_miscdrv_rdwr_spinlock/2_miscdrv_rdwr_spinlock.c
[ ... ]
static int buggy...