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

The mutex interruptible and killable variants

As you have already learned, the mutex_lock_interruptible() API is used when the driver (or module) is willing to acknowledge any (user space) signal interrupting it (and returns -ERESTARTSYS to tell the kernel VFS layer to perform signal handling; the user space system call will fail with errno set to EINTR). An example can be found in the module handling code in the kernel, within the delete_module(2) system call (which rmmod(8) invokes):

// kernel/module.c
[ ... ]
SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
unsigned int, flags)
{
struct module *mod;
[ ... ]
if (!capable(CAP_SYS_MODULE) || modules_disabled)
return -EPERM;
[ ... ]
if (mutex_lock_interruptible(&module_mutex) != 0)
return -EINTR;
mod = find_module(name);
[ ... ]
out:
mutex_unlock(&module_mutex);
return ret;
}

Notice how the API returns -EINTR on failure. (The SYSCALL_DEFINEn...