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

Copying data from kernel to user space and vice versa

A primary job of the device driver is to enable user space applications to transparently both read and write data to the peripheral hardware device (typically a chip of some sort; it may not be hardware at all though), treating the device as though it were simply a regular file. Thus, to read data from the device, the application opens the device file corresponding to that device, thus obtaining a file descriptor, and then simply issues a read(2) system call using that fd (step 1 in Figure 1.7)! The kernel VFS intercepts the read, and, as we have seen, has control flow to the underlying device driver's read method (which is a C function, of course). The driver code now "talks" to the hardware device, actually performing the I/O, the read operation. (The specifics of how exactly the hardware read (or write) is performed depends very much on the type of hardware – is it a memory-mapped device, a port, a network chip, and so on? We will not delve further into this here; the next chapter does.) The driver, having read data from the device, now places this data into a kernel buffer, kbuf (step 2 in the following diagram. Of course, we assume the driver author allocated memory for it via [k|v]malloc() or another suitable kernel API).

We now have the hardware device data in a kernel space buffer. How should we transfer it to the user space process's memory buffer? We shall exploit kernel APIs that make it easy to do so; this is covered next.