Now I reading the greatest book “FreeBSD device drivers” by Joseph Kong. The book covers FreeBSD version 8, but now versions 12.1, 12.0 and 11.3 are actual (I use the version 12.1) and some code aren’t compile. For example, the pointless driver (section “Implementing sysctls, Part 1”, chapter 3 on page 41). Because I testing and studying all code from the book, I adapted this driver for my version of FreeBSD. You can clone my repo with the pointless driver and other code from the book from my GitHub.
Let’s studying FreeBSD together, because it’s the greatest OS!