This section lists the function codes and parameters for the $IO_SETUP system service.
IO$_READVBLK IO$_READLBLK IO$_WRITEVBLK IO$_WRITELBLK
bufobj - user's buffer
iosobj — I/O Status Area (IOSA)
astadr — Completion AST routine
flags — longword mask
return_fandle — fandle address
