... in your setup. All shops are different. To each their own. There's no private/protected scaffolding in the Linux kernel to give the most obvious example.
I don't know anything about kernel programming, but I assume that there's some very, very strict conventions about how the various parts of the Linux kernel interact, and nothing gets accepted for merging unless you follow them. This would be similar to imposing scope/visibility constraints at the language level, but considering C doesn't have anything for that, an extremely strict development process is the best you can do.