The if_nameindex(), if_nametoindex(), and if_indextoname() functions use the SIOCGIFNAMEINDEX (Get Interface Name/Index Table) ioctl, which returns the Interface Name/Index Table for a PFS. The command and output arguments are defined in the BPXYIOCC macro, and are described in the discussion of the SIOCGIFNAMEINDEX ioctl command inw_ioctl (BPX1IOC, BPX4IOC) — Control I/O in z/OS UNIX System Services Programming: Assembler Callable Services Reference.