In this chapter, we covered an important aspect of device driver authors – how exactly you can interface between user and kernel (driver) space. We walked you through several interfacing methods; we began with an older one, which is interfacing via the venerable proc filesystem (and then mentioned why it's not the preferred method for driver authors). We then moved on to interfacing via the newer 2.6-based sysfs. This turns out to be the preferred interface for the user space, at least for a device driver. Sysfs has limitations, though (recall the one-value-per-sysfs-file rule). Thus, using the completely free-format debugfs interfacing technique makes writing debug (and other) interfaces very simple and powerful indeed. The netlink socket is a powerful interfacing technology and is used by the network subsystem, udev, and a few drivers; it does require some knowledge on socket programming and the kernel socket buffer, though. To perform generic command...
Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization
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Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization
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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)
Preface
Section 1: Character Device Driver Basics
Free Chapter
Writing a Simple misc Character Device Driver
User-Kernel Communication Pathways
Working with Hardware I/O Memory
Handling Hardware Interrupts
Working with Kernel Timers, Threads, and Workqueues
Section 2: Delving Deeper
Kernel Synchronization - Part 1
Kernel Synchronization - Part 2
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