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

Our simple work queue kernel module running it

Let's take it for a spin! Take a look at the following screenshot:

Figure 5.12 – Our workq_simple.ko LKM with the work queue function execution highlighted

Let's take a look at this code in more detail:

  • Via our lkm helper script, we build and then insmod(8) the kernel module; that is, workq_simple.ko.
  • The kernel log is displayed via dmesg(1):
    • Here, the workqueue and kernel timer are initialized and armed within the init method.
    • The timer expires (in approximately 420 ms); you can see its printks (showing timed out... and the value of our data variable).
    • It invokes the schedule_work() API, causing our workqueue function to run.
    • As highlighted in the preceding screenshot, our work queue function, work_func(), indeed runs; it displays the data variable's current value, proving that it correctly gained access to our "context" or private...