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

Interrupt context guidelines what to do and what not to do

The interrupt handler routine is your typical C code, with some caveats. A few key points regarding the design and implementation of your hardware interrupt handler are as follows:

  • The handler runs in an interrupt context, so do not block: First and foremost, this code always runs in an interrupt context; that is, an atomic context. On a preemptible kernel, preemption is disabled, so there are some limitations regarding what it can and cannot do. In particular, it cannot do anything that directly or indirectly invokes the scheduler (schedule())!
    In effect, you cannot do the following:
    • Transfer data to and from kernel to user space as it might cause a page fault, which isn't allowed in an atomic context.
    • Use the GFP_KERNEL flag in memory allocation. You must use the GFP_ATOMIC flag so that the allocation is non-blocking it either succeeds or fails immediately.
    • Invoke any API that's blocking (that,...