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)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

The four procfs files we will create

To help clearly illustrate the usage of procfs as an interfacing technology, we will have our kernel module create a directory under /proc. Within that directory, it will create four procfs (pseudo) files. Note that, by default, all procfs files have their owner:group attributes as root:root. Now, create a directory called /proc/proc_simple_intf and, under it, create four (pseudo) files. The names and attributes of the four procfs (pseudo) files under the /proc/proc_simple_intf directory, are shown in the following table:

Name of procfs 'file' R: action on read callback, invoked via user space read W: action on write callback, invoked via user space write Procfs 'file' permissions
llkdproc_dbg_level Retrieves (to the user space) the current value of the global variable; that is,
debug_level
Updates the debug_level global variable to the value written by the user space 0644
llkdproc_show_pgoff Retrieves...