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

Helper debugfs APIs for working on numeric globals

You have just learned how to use the debugfs_create_u32() helper API to set up a debugfs file to read/write an unsigned 32-bit integer global. The fact is, the debugfs layer provides a bunch of similar "helper" APIs to implicitly read/write on numeric (integer) global variables within your module.

The helper routines for creating debugfs entries that can read/write different bit size unsigned integer (8-, 16-, 32-, and 64-bit) globals follow. The last parameter is the key one the address of the global integer within the kernel/module:

// include/linux/debugfs.h
struct dentry *debugfs_create_u8(const char *name, umode_t mode,
struct dentry *parent, u8 *value);
struct dentry *debugfs_create_u16(const char *name, umode_t mode,
struct dentry *parent, u16 *value);
struct dentry *debugfs_create_u32(const char *name, umode_t mode,
struct dentry *parent, u32 *value);
struct dentry...