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

Efficiently searching a bitmask

Several algorithms depend on performing a really fast search of a bitmask; several scheduling algorithms (such as SCHED_FIFO and SCHED_RR, which you learned about in the companion guide Linux Kernel Programming - Chapter 10The CPU Scheduler – Part 1, and Chapter 11The CPU Scheduler – Part 2) often internally require this. Implementing this efficiently becomes important (especially for OS-level performance-sensitive code paths). Hence, the kernel provides a few APIs to scan a given bitmask (these prototypes are found in include/asm-generic/bitops/find.h):

  • unsigned long find_first_bit(const unsigned long *addr, unsigned long size): Finds the first set bit in a memory region; returns the bit number of the first set bit, else (no bits are set) returns @size.
  • unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size): Finds the first cleared bit in a memory region...