On Alpha and Integrity server systems, performs operations on the
    set of Fast Path devices and CPUs enabled for Fast Path use.

    The $IO_FASTPATHW system service is functionally equivalent to
    the $IO_FASTPATH service except that it completes synchronously.
    That is, it returns after the operation is complete.

    Format

      SYS$IO_FASTPATHW  efn, cpu_mask, function_code, [iosb],

                        [astadr], [astprm], [,[mask_length]]

    C Prototype

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

                            int function_code, struct_iosb *iosb,

                            void (*astadr)(_ _unknown_params),

                            _ _int64 astprm, ...) ;)