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

Reader-writer spinlock interfaces

Having used spinlocks, using the reader-writer variant is straightforward; the lock data type is abstracted as the rwlock_t structure (in place of spinlock_t) and, in terms of API names, simply substitute read or write in place of spin:

#include <linux/rwlock.h>
rwlock_t mylist_lock;

The most basic APIs of the reader-writer spinlock are as follows:

void read_lock(rwlock_t *lock);
void write_lock(rwlock_t *lock);

As an example, the kernel's tty layer has code to handle a Secure Attention Key (SAK); the SAK is a security feature, a means to prevent a Trojan horse-type credentials hack by killing all processes associated with the TTY device. This will happen when the user presses the SAK ( When this actually happens (that is, when the user presses the SAK, mapped to the Alt-SysRq-k sequence by default), within its code path, it has to iterate over all tasks...