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

Examples of using refcount_t within the kernel code base

In one of our demo kernel modules regarding kernel threads (in ch15/kthread_simple/kthread_simple.c), we created a kernel thread and then employed the get_task_struct() inline function to mark the kernel thread's task structure as being in use. As you can now guess, the get_task_struct() routine increments the task structure's reference counter – a refcount_t variable named usage – via the refcount_inc() API:

// include/linux/sched/task.h
static inline struct task_struct *get_task_struct(struct task_struct *t)
return t;

The converse routine, put_task_struct(), performs the subsequent decrement on the reference counter. The actual routine employed by it internally, refcount_dec_and_test(), tests whether the new refcount value has dropped to 0; if so, it returns true, and if this is the case, it implies that the task structure isn't being...