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

Writing the user space netlink socket application

Follow these steps get the user space application running:

  1. The first thing we must do is get ourselves a socket. Traditionally, a socket is defined as an endpoint of communication; thus, a pair of sockets forms a connection. We will use the socket(2) system call to do this. Its signature is
    int socket(int domain, int type, int protocol);.

Without going into too much detail, here's what we do:

    • We specify domain as part of the special PF_NETLINK family, thus requesting a netlink socket.
    • Set type to SOCK_RAW using a raw socket (effectively skipping the transport layer).
    • protocol is the protocol to use. Since we're using a raw socket, the protocol is left to be implemented either by us or by the kernel; having the kernel netlink code do this is the right approach. Here, we use an unused protocol number; that is, 31.
  1. The next step is to bind the socket via the usual bind(2) system call semantics. First, we must...