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

A few misc procfs APIs

Let's conclude this section by looking at a few remaining miscellaneous procfs APIs. You can create a symbolic or soft link within /proc by using the proc_symlink() function.

Next, the proc_create_single_data() API can be very useful; it's used as a "shortcut", where you require just a "read" method to be attached to a procfs file:

struct proc_dir_entry *proc_create_single_data(const char *name, umode_t mode, struct     
proc_dir_entry *parent, int (*show)(struct seq_file *, void *),
void *data);

Using this API thus eliminates the need for a separate fops data structure. We can use this function to create and work with our second procfs file the llkdproc_show_pgoff file:

... proc_create_single_data(PROC_FILE2, PROC_FILE2_PERMS, gprocdir, proc_show_pgoff, 0) ...

When read from the user space, the kernel's VFS and proc layer code paths will invoke the registered method the proc_show_pgoff() function of our...