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

How Linux prioritizes activities

Now that you have learned about so many areas across the gamut, we can zoom out and see how the Linux kernel prioritizes things. The following (conceptual) diagram - a superset of earlier similar diagrams - neatly sums this up:

Figure 4.13 – Relative priorities across the full stack - user, kernel process context, and kernel interrupt contexts

This diagram is pretty self-explanatory, so please study it carefully.

In this lengthy section, you have learned about interrupt handling via both the top-half and bottom-half mechanisms, the reasons for them in the first place, and how they are organized and to be used by drivers. You now understand that all bottom-half mechanisms are internally implemented via softirqs; the tasklet is the primary bottom-half mechanism that you, as a driver author, have easy access to use. This, of course, does not imply you must use them – if you can get away with simply using a top-half only, or, even...