FreeBSD Device Drivers Book

A comprehensive, open-source guide by Edson Brandi that takes readers from basic C and UNIX concepts to writing production-quality FreeBSD 14.x device drivers through 38 chapters and extensive hands-on labs.

From First Steps to Kernel Mastery

by Edson Brandi · Version 2.0 (April 2026)

FreeBSD Device Drivers: From First Steps to Kernel Mastery is a free, open-source book that takes you from "I've never written kernel code" to "I can write, debug, and submit production-quality FreeBSD drivers." It is a guided course rather than a reference, structured around 38 chapters, 6 appendices, and dozens of hands-on labs that compile and load on a real FreeBSD 14.x system.

The book is aimed at readers who are willing to learn rather than are already qualified. It begins with UNIX fundamentals and the C language, walks step by step through every concept the kernel will demand of you, and only then opens the door to driver development. By the time you reach DMA, interrupts, and PCI work, the vocabulary feels earned, not imposed.

"Kernel programming is still programming, only with more explicit rules, greater responsibility, and a bit more power. Once you understand that, the fear gives way to excitement."(from Chapter 1)

There are excellent FreeBSD kernel references already, including man 9, the Architecture Handbook, and the Newbus papers. What has been missing is a single text that:

Starts from zero. UNIX, C, and the FreeBSD environment are taught before any kernel code is written.
Targets FreeBSD 14.x specifically. Every API, every example, every lab was verified against the FreeBSD 14.3 source tree.
Treats labs as first-class. Roughly half of the recommended study time is hands-on. The same patterns (attach, cleanup, locking) recur across chapters until they become reflex.
Builds one driver across the whole book. The myfirst driver evolves chapter by chapter, gaining synchronisation, then hardware access, then interrupts, then DMA. You see the same code mature in your own hands.
Covers the full lifecycle. From "Hello Kernel Module" all the way to submitting a Phabricator review and shepherding a driver into the FreeBSD tree.

Target Audience:

Beginners who know little about C, UNIX, or kernels but are willing to learn.
Developers curious about how operating systems actually work under the hood.
Professionals who already use FreeBSD (or similar systems) and want to deepen their knowledge by learning how drivers are built in practice.

Structure: