File permissions in the kernel

Is that because permission bits are the only thing still using octal today? If they were hex, there are plenty of other "magic" hex literals out there to cause confusion as to what a specific hex literal might mean (particularly when assigned away from its usage for some bitflips). While the underscore train is annoying, I personally try to avoid "magic constants", even permission bits and instead use the S_* macros and even things like STDIN_FILENO and friends.