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

Initializing the tasklet

The tasklet_init() function initializes a tasklet; its signature is as follows:

#include <linux/interrupt.h>
void tasklet_init(struct tasklet_struct *t, void (*func)(unsigned long), unsigned long data);

Let's check out its parameters:

  • struct tasklet_struct *t: This structure is the metadata representing the tasklet. As you already know, a pointer, by itself, has no memory! Remember to allocate memory to the data structure and then pass the pointer here.
  • void (*func)(unsigned long): This is the tasklet function itself – the "bottom half" that runs once the hardirq completes; this bottom half function performs the majority of the interrupt handling process.
  • unsigned long data: Any data item you wish to pass along to the tasklet routine (a cookie).

Where should this initialization work be performed? Typically, this is done within the driver's probe (or init) function. So, now that it's been initialized and is ready...