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

procfs is off-bounds to driver authors

Even though we could use the proc filesystem to interface with a user mode app, there is an important point to note here! You must realize that procfs is, like many similar facilities within the kernel, an Application Binary Interface (ABI). The kernel community makes no promises that it remains stable and exactly the way it is today, just as is the case with the kernel APIs and their internal data structures as well. In fact, ever since the 2.6 kernel, the kernel folks have made this very clear  device driver authors (and the like) are not supposed to use procfs for their own purposes or their interfaces, debug or otherwise. Earlier, with 2.6 Linux, it was quite common to use proc for said purposes (abused, as per the kernel community, as proc is meant for kernel internal use only!).

So, if procfs is considered off-bounds, or deprecated, to us as driver authors, then what facility do we use to communicate with user space processes...