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

A quick summary of the workflow

When using the kernel-global workqueue, a simple pattern (workflow) emerges:

  1. Initialize the work task.
  2. At the appropriate point in time, schedule it to execute (perhaps with a delay and/or on a particular CPU core).
  3. Clean up. Typically, in the kernel module (or driver's) cleanup code path, cancel it. (Preferably, do this with synchronization so that any pending work tasks are completed first. Here, we will stick to employing the recommended cancel*work*() routines, avoiding the flush_*() ones).

Let's summarize this using a table:

Using the kernel-global workqueue Regular work task  Delayed work task  Execute work task on given CPU
1. Initialization  INIT_WORK() INIT_DELAYED_WORK() < either immediate or delayed's fine >
2. Schedule work task to execute schedule_work() schedule_delayed_work() schedule_delayed_work_on()
3. Cancel (or flush) it; foo_sync() to ensure it's complete cancel_work_sync() cancel_delayed_work_sync...