FreeBSD device drivers

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... » read more