The processing of output files without labels is requested by means of the operand LABEL=NO of the FILE macro or the operand LABEL-TYPE=*NO of the ADD-FILE-LINK command.
DMS expects a file without labels to be created. Nevertheless, it first checks whether the tape already contains standard labels. If a VOL1 label is found, DMS proceeds to check the other labels. If there is no VOL1 label on the tape, the tape is immediately positioned and the user can proceed with file processing.
Checking labels
If the tape contains a VOL1 label, DMS first checks its VSN (and issues message DMS0DA1 to the operator in the case of an error). If the user has not requested a specific tape (DEVICE or DEVICE-TYPE=WORK), or if the volume list (VOLUME=) is exhausted, the operator is requested via message DMS0DFB to assign a tape to the job.
DMS then checks the HDR labels of the first file on the tape in order to determine whether file access is permitted. In the event of an error, DMS sends message DM0DD7 to the user. If authorized, the user can ignore this message.
Next, the access type (HDR3) and the expiration date (HDR1) are checked. If a retention period still exists for the file on the tape, or if the access type is read-only (corresponding to ACCESS=READ), DMS sends message DMS0DA3 to the user. If authorized, the user can ignore this message and proceed with file processing.
Finally, the operator is asked whether the user may write a file without labels on a standard tape. The operator can permit or forbid this; in the latter case, an error routine in the user program is called and the program is terminated.
Positioning and writing a tape mark
The tape is positioned as specified in the FSEQ operand of the FILE command, in the FILE-SEQUENCE operand of the ADD-FILE-LINK command, or according to the FSEQ value in the catalog entry.
If FSEQ=1 or FILE-SEQUENCE=1 applies, i.e. if this is the first file on the tape, the tape is positioned to BOT (Beginning-Of-Tape) and, if TPMARK=YES or TAPE-MARK-WRITE=*YES applies, a tape mark is written.