devptr

    OpenVMS usage char_string
    type          character string
    access        read only
    mechanism     by reference
    The address of the device name string. The device name must be
    supplied in allocation-class device name (ALLDEVNAM) format, but
    any leading underscore or trailing colon are ignored.

 fidptr

    OpenVMS usage address
    type          file identification
    access        read only
    mechanism     by reference
    The address of the three-word file identification.

 bufptr

    OpenVMS usage char_string
    type          character string
    access        write only
    mechanism     by reference
    The address of a string buffer into which to store the file name
    string.

 buflen

    OpenVMS usage longword
    type          longword (unsigned)
    access        read only
    mechanism     by value
    The maximum length of the string buffer.