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

An interfacing example with debugfs

Debugfs, being deliberately designed with a "no particular rules" mindset, makes it the ideal interface to use for debug purposes. Why? It allows you to construct any arbitrary byte stream and send it off to the user space, including a binary "blob" with the debugfs_create_blob() API.

Our previous example kernel modules with procfs and sysfs constructed and used three to four (pseudo) files. For a quick demo with debugfs, we shall just stick to two "files":

  • llkd_dbgfs_show_drvctx: As you'll have no doubt guessed, when read, it will cause the current content of our (by now familiar) "driver context" data structure to be dumped to the console; we shall ensure the pseudo file's mode is read-only (by root).
  • llkd_dbgfs_debug_level: This file's mode shall be read-write (by root only); when read, it will display the current value of debug_level; when an integer is written to it, we shall update...