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 simple demo – creating a kernel thread

The primary API for creating kernel threads (that's exposed to us module/driver authors) is kthread_create(); it's a macro that invokes the kthread_create_on_node() API. The fact is, calling kthread_create() alone isn't sufficient to have your kernel thread do anything useful; this is because, while this macro does create the kernel thread, you need to make it a candidate for the scheduler by setting it's stated to running and waking it up. This can be done with the wake_up_process() API (once successful, it's enqueued onto a CPU runqueue, which makes it schedulable so that it runs in the near future). The good news is that the kthread_run() helper macro can be used to invoke both kthread_create() and wake_up_process() in one go. Let's take a look at its implementation in the kernel:

// include/linux/kthread.h
* kthread_run - create and wake a thread.
* @threadfn: the function...