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

Softirqs and concurrency

As we learned with regard to tasklets, a number of points with regard to concurrency must be understood with respect to softirqs:

  • As noted with tasklets (on SMP), a tasklet will never run in parallel with itself; this is a feature that makes it easier to use. This isn't true of softirqs: the same softirq vector can indeed run in parallel with itself on another CPU! Thus, the softirq vector code has to be especially careful with the use of locking (and deadlock avoidance).
  • A softirq can always be interrupted by a hardirq, including the IRQ that caused it to be raised (this is because, as with tasklets, softirqs run with all interrupts enabled on the local core).
  • A softirq cannot preempt another currently executing softirq, even though they have priority levels; they are consumed in priority order.
  • The reality is that the kernel provides APIs such as spin_lock_bh(), which allow you to disable softirq processing while the...