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

Looking up the new mapping via /proc/iomem

Once you have performed a mapping (via one of the just-covered [devm_]ioremap*()APIs), it can actually be seen via the read-only pseudo-file; that is, /proc/iomem. The reality is that a new entry under /proc/iomem is generated when you successfully call request_mem_region()Viewing it requires root access (more correctly, you can view it as non-root but will only see all the addresses as 0; this is for security purposes). So, let's take a look at this on our trusty x86_64 Ubuntu guest VM. In the following output, due to lack of space and for clarity, we'll show it partially truncated:

$ sudo cat /proc/iomem 
[sudo] password for llkd:
00000000-00000fff : Reserved
00001000-0009fbff : System RAM
0009fc00-0009ffff : Reserved
000a0000-000bffff : PCI Bus 0000:00
000c0000-000c7fff : Video ROM
000e2000-000ef3ff : Adapter ROM
000f0000-000fffff : Reserved
000f0000-000fffff : System ROM
00100000-3ffeffff : System RAM