p1
    OpenVMS usage:buffer
    type:         vector byte (unsigned)
    access:       read only
    mechanism:    (Alpha and I64) by 32- or 64-bit reference
                  (VAX) by 32-bit reference
    The address of the buffer to receive the incoming data. The
    length of this buffer is specified by the p2 argument.
 p2
    OpenVMS usage:buffer_length
    type:
    access:       quadword unsigned (Alpha and I64); longword
    unsigned (VAX)
    mechanism:    read only
                  (Alpha and I64) by 64-bit value
    The length (in bytes) of the buffer available to hold the
    incoming data. The address of this buffer is specified by the
    p1 argument.
 p3
    OpenVMS usage:socket_name
    type:         vector byte (unsigned)
    access:       read only
    mechanism:    by item_list_3 descriptor
    The remote port number and IP address of the source of the
    datagram or raw IP message (not TCP). The p3 argument is the
    address of an item_list_3 descriptor that points to the socket
    address structure into which the remote port number and IP
    address of the message source is written.
 p4
    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Longword of flags to specify attributes for the read operations.
    The following table lists the available read flags.
    Read Flag          Description
    TCPIP$C_MSG_OOB    Reads an out-of-band byte.
    TCPIP$C_MSG_PEEK   Reads a message but leaves the message in the
                       queue.
    TCPIP$C_MSG_NBIO   Does not block the I/O operation if the
                       receive queue is empty (similar to using
                       IO$M_NOWAIT).
    TCPIP$C_MSG_PURGE  Flushes data from the queue (similar to using
                       IO$M_PURGE).
    TCPIP$C_MSG_       Blocks the completion of the operation until
    BLOCKALL           the buffer is filled completely or until the
                       connection is closed (similar to using IO$M_
                       LOCKBUF).
 p6
    OpenVMS usage:buffer_list
    type:         vector byte (unsigned)
    access:       read only
    mechanism:    (Alpha and I64) by 32- or 64-bit
                  descriptor-fixed-length descriptor
                  (VAX) by 32-bit descriptor-fixed-length descriptor
    Output buffer list describing one or more buffers to hold the
    incoming data. The p6 argument is the 32- or 64-bit address (on
    Alpha and I64 systems) or the 32-bit address (on VAX systems)
    of a descriptor that points to a output buffer list. Buffers
    are filled in the order specified by the output buffer list. The
    transfer-length value returned in the I/O status block is the
    total number of bytes transferred to all buffers.
    If you use the p1 and p2 arguments, do not use the p6 argument;
    they are mutually exclusive.