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

Seeing a kernel bug an Oops!

Let's make it happen a kernel bug! Exciting, yes!?

Okay, to create a kernel bug, we must ensure that when we remove (unload) the kernel module, the API that cleans up (deletes) all the debugfs files, debugfs_remove_recursive(), is not invoked. Thus, after each module is removed, our debugfs directory and files seem to be present! However, if you try and operate on read/write any of them, they'll be in an orphaned state and, hence, upon trying to dereference its metadata, the internal debugfs code paths will perform an invalid memory reference, resulting in a (kernel-level) bug.

In the kernel space, a bug is a very serious thing indeed; in theory, it should never, ever happen! This is called an Oops; as part of handling this, an internal kernel function is called, which dumps useful diagnostic information via printk to the in-memory kernel log buffer, as well as to the console device (on production...