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

Internally implementing the threaded interrupt

As we mentioned previously, if the primary handler is null and the thread function is non-null, the kernel uses a default primary handler. The function is called irq_default_primary_handler() and all it does is return the IRQ_WAKE_THREAD value, thus waking up (and making schedulable) the kernel thread.

Furthermore, the actual kernel thread that runs your thread_fn routine is created within the code of the request_threaded_irq() API. The call graph (as of version 5.4.0 of the Linux kernel) is as follows:

   kernel/irq/manage.c:request_threaded_irq() --  __setup_irq() --
setup_irq_thread() -- kernel/kthread.c:kthread_create()

The invocation of the kthread_create() API is as follows. Here, you can clearly see how the format of the new kernel thread's name will be in irq/irq#-name format:

t = kthread_create(irq_thread, new, "irq/%d-%s", irq, new->name);

Here (we...