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

Cleaning up – canceling or flushing your work task

At some point, you will want to ensure that your work task(s) have actually completed execution. You may wish to do this before destroying your workqueue (assuming it's a custom created one and not the kernel-global one) or, more likely, when using the kernel-global workqueue in the cleanup method of your LKM or driver. The typical API to use here is cancel_[delayed_]work[_sync](). Its variations and signatures are as follows:

bool cancel_work_sync(struct work_struct *work);
bool cancel_delayed_work(struct delayed_work *dwork);
bool cancel_delayed_work_sync(struct delayed_work *dwork);

It's quite simple, really: use cancel_work_sync() once you have used the INIT_WORK() and schedule_work() routines; use the latter two when you've delayed your work task. Notice that two of the routines are suffixed with _sync; this implies that the cancellation is synchronous the kernel will wait until your work tasks have...