The user-written FILEIO routine is used to handle DECTPU file
    operations. The name of this routine can be either your own
    file I/O routine or the name of the DECTPU file I/O routine
    (TPU$FILEIO).

    Format

      FILEIO  code ,stream ,data

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (usigned)
    access:       write only
    mechanism:    by reference

    Longword condition value. Most utility routines return a
    condition value in R0. Condition values that this routine can
    return are listed under Condition Values Returned.

2  –  Arguments

 code

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Item code specifying a DECTPU function. The code argument is the
    address of a longword containing an item code from DECTPU, which
    specifies a function to perform.

 stream

    OpenVMS usage:unspecified
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference
    File description. The stream argument is the address of a data
    structure containing four longwords. This data structure is used
    to describe the file to be manipulated.

 data

    OpenVMS usage:item_list_3
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference
    Stream data. The data argument is either the address of an item
    list or the address of a descriptor.

                                   NOTE

       The value of this parameter depends on which item code you
       specify.

3  –  Description

    The bound procedure value of this routine is specified in the
    item list built by the callback routine. This routine is called
    to perform file operations. Instead of using your own file I/O
    routine, you can call TPU$FILEIO and pass it the parameters for
    any file operation you do not want to handle. Note, however, that
    TPU$FILEIO must handle all I/O requests for any file it opens.
    Also, if it does not open the file, it cannot handle any I/O
    requests for the file. In other words, you cannot mix the file
    operations between your own file I/O routine and the one supplied
    by DECTPU.

4  –  Condition Values Returned

    The condition values returned are determined by the user and
    should indicate success or failure of the operation.