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

sed2 driver code implementation

In terms of code, the ioctl() method's code within the sed2 driver for the encrypt operation is as follows (for clarity, we won't show all the error checking code here; we will show only the most relevant parts). You can find the full code at ch5/sed2/:

// ch5/sed2/sed2_driver/sed2_drv.c
[ ... ]
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 36)
static long ioctl_miscdrv(struct file *filp, unsigned int cmd, unsigned long arg)
#else
static int ioctl_miscdrv(struct inode *ino, struct file *filp, unsigned int cmd, unsigned long arg)
#endif
{
struct stMyCtx *priv = gpriv;

[ ... ]
switch (cmd) {
case IOCTL_LLKD_SED_IOC_ENCRYPT_MSG: /* kthread: encrypts the msg passed in */
[ ... ]
if (atomic_read(&priv->msg_state) == XF_ENCRYPT) { // already encrypted?
pr_notice("encrypt op: message is currently encrypted; aborting op...\n");
return -EBADRQC; /* 'Invalid request code...