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

Querying and setting the scheduling policy/priority of a kernel thread

In closing, how can you query and/or change the scheduling policy and (real-time) priority of a kernel thread? The kernel provides APIs for this (the sched_setscheduler_nocheck() API is often used within the kernel). As a practical example, the kernel will require kernel threads for the purpose of servicing interrupts  the threaded interrupt model, which we covered in Chapter 4, Handling Hardware Interrupts, in the Internally implementing the threaded interrupt section).

It creates these threads (via kthread_create()) and changes their scheduling policy and real-time priority via the sched_setscheduler_nocheck() API. We won't explicitly cover their usage here as we covered this in the companion guide Linux Kernel Programming - Chapter 11, The CPU Scheduler Part 2. It's interesting: the sched_setscheduler_nocheck() API is just a simple...