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

Enabling and disabling IRQs

Typically, it's the core kernel (and/or arch-specific) code that handles low-level interrupt management. This includes doing things such as masking them as and when required. Nevertheless, some drivers, as well as the OS, require fine-grained control when enabling/disabling hardware interrupts. As your driver or module code runs with kernel privileges, the kernel provides (exported) helper routines that allow you to do exactly this:

Brief comment API or helper routine
Disable/enable all interrupts on the local processor
Unconditionally disables all interrupts on the local (current) processor core. local_irq_disable()
Unconditionally enables all interrupts on the local (current) processor core. local_irq_enable()
Saves the state (interrupt mask) of, and then disables all interrupts on  the local (current) processor core. The state is saved in the flags parameter that's passed. local_irq_save(unsigned long flags);
Restores the...