setup(2) -- Linux man page
NAMEsetup - setup devices and file systems, mount root file system
DESCRIPTIONsetup is called once from within linux/init/main.c. It calls initialization functions for devices and file systems configured into the kernel and then mounts the root file system.
RETURN VALUEsetup always returns -1 for a user process.
- Always, for a user process.
CONFORMING TOThis function is Linux specific, and should not be used in programs intended to be portable, or indeed in any programs at all. Since Linux 2.1.121, no such function exists anymore. The calling sequence varied: it has had a single parameter void * BIOS and at other times a single parameter int magic.