... that's pretty much the point of ioctl - a syscall multiplexer in the context of a fd. 9 is pretty low - check out /dev/cdrom or /dev/dri/* if you want to see a lot.

ioctl is pretty much a generic syscall interface (other OSes have similar things). An awful lot of Linux subsystems export an awful lot of syscalls through it; probably easily a four or five figure number (literature typically claims that Linux has only a couple hundred syscalls).