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

Running the tasklet

The tasklet is the bottom half. Thus, in the top half, which is your hardirq handler routine, the last thing you should do before returning is "schedule" your tasklet to execute:

void tasklet_schedule(struct tasklet_struct *t);

Simply pass the pointer to your (initialized) tasklet structure to the tasklet_schedule() API; the kernel will handle the rest. What does the kernel do? It schedules this tasklet to execute; practically speaking, your tasklet's function code is guaranteed to run before control returns to the task that was interrupted in the first place (be it a user or kernel thread). More details can be found in the Understanding how the kernel runs softirqs section.

Regarding the tasklet, there are a few things you need to be clear about:

  • The tasklet executes its code in an interrupt (atomic) context; it's actually a softirq context. So, remember, all the restrictions that apply to top halves apply here too! (Check...