On Alpha and Integrity server systems, provides the ability to
    control the set of Fast Path devices and their assignment to CPUs
    enabled for Fast Path use.

    Format

      SYS$IO_FASTPATH  efn, cpu_mask,function_code, [iosb], [astadr],

                       [astprm] [,[mask_length]]

    C Prototype

      int sys$io_fastpath  (unsigned int efn, UINT32_PQ cpu_mask,

                           int function_code, struct_iosb *iosb,

                           void (*astadr)(__unknown_params), __int64

                           astprm, ...) ;)