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

sed2 the design

Our sed v2 (sed2; code: ch5/sed2/) mini-project is very similar to our sed1 project. The key difference is that this time, we'll carry out the "work" via a kernel thread created by the driver for just this purpose. The key differences between this version and the previous one are as follows:

  • There's just one global shared memory buffer for holding the metadata, along with the payload; that is, the message to encrypt/decrypt. This is the struct sed_ds->shmem member within our driver context structure, struct stMyCtx.
  • The work of encryption/decryption is now performed within a kernel thread (that this driver spawns); we keep the kernel thread asleep. Only when work arises does the driver wake up the kthread and have it consume (execute) the work.
  • We now run the kernel timer within the kthread's context and show if it expires prematurely (indicating that the deadline wasn't met).
  • A quick test reveals that eliminating...