chan

    OpenVMS usage:channel
    type:         word (unsigned)
    access:       read only
    mechanism:    by value
    Number of the I/O channel assigned to the device about which
    information is desired. The chan argument is a word containing
    this number.

    To identify a device to $DEVICE_PATH_SCAN, you can specify either
    the chan or devnam parameters, but you should not specify both.
    If you specify both arguments, the chan argument is used.

    If you specify neither chan nor devnam, $DEVICE_PATH_SCAN uses a
    default value of 0 for chan.

 devnam

    OpenVMS usage:device_name
    type:         character-coded text string
    access:       read only
    mechanism:    by descriptor-fixed-length string descriptor
    The name of the device about which $DEVICE_PATH_SCAN is to
    return path information. The devnam argument is the address of
    a character string descriptor pointing to this name string.

    The device name string can be either a physical device name
    or a logical name. If the first character in the string is an
    underscore (_),  the string is considered a physical device name;
    otherwise, the string is considered a logical name and logical
    name translation is performed until either a physical device name
    is found or the system default number of translations has been
    performed.

    If the device name string contains a colon (:),  the colon and
    the characters that follow it are ignored.

    To identify a device to $DEVICE_PATH_SCAN, you can specify either
    the chan or devnam argument, but you should not specify both. If
    both arguments are specified, the chan argument is used.

    If you specify neither chan nor devnam, $DEVICE_PATH_SCAN uses a
    default value of 0 for chan.

 itmlst

    OpenVMS usage:item_list_3
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Item list specifying which information about the device is to be
    returned. The itmlst argument is the address of a list of item
    descriptors, each of which describes an item of information. The
    list of item descriptors is terminated by a longword of 0.

    Refer to the VSI OpenVMS System Services Reference Manual to view
    the item code diagram and descriptor fields table.

 contxt

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference
    Value used to indicate the current position of a $DEVICE_PATH_
    SCAN search. The contxt argument is the address of the longword
    that receives this information. On the initial call, the longword
    should contain 0.

 nullarg

    OpenVMS usage:null_arg
    type:         quadword (unsigned)
    access:       read only
    mechanism:    by reference
    Placeholding argument Reserved to VSI.