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)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

Trying out the dynamic debug_level procfs control

First, let's check out the "driver context" data structure that we shall use throughout this chapter (in fact, we first used it in the previous chapter):

// ch2/procfs_simple_intf/procfs_simple_intf.c
[ ... ]
/* Borrowed from ch1; the 'driver context' data structure;
* all relevant 'state info' reg the driver and (fictional) 'device'
* is maintained here.
*/
struct drv_ctx {
int tx, rx, err, myword, power;
u32 config1; /* treated as equivalent to 'debug level' of our driver */
u32 config2;
u64 config3;
#define MAXBYTES 128
char oursecret[MAXBYTES];
};
static struct drv_ctx *gdrvctx;
static int debug_level; /* 'off' (0) by default ... */

Here, we can also see that we have a global integer named debug_level; this will provide dynamic control over the debug verbosity of the "project". The debug level is assigned a range of [0-2], where we have the following...