• The exit can change the volume serial number in TEPMVOL in the main parameter list to a new volume serial. The system will update the JFCB or JFCB extension used during OPEN or EOV; the system also will update the SWA copy of the JFCB or JFCB extension unless the application program prevented it by turning on bit JFCNWRIT. This bit is honored during OPEN, not during EOV. The system will update the catalog if the catalog retrieved it or the user specified CATLG for the DD DISP=parameter.

  The system will enqueue on the new volume serial. If the enqueue is successful, then the system will dequeue the original volume serial. If the enqueue fails, even if it is being owned by the same job, the system will reject the tape. The system then will reissue the original mount request. It can be a specific request or a nonspecific request.

• The exit can change the volume serial number in TEPMVOL in the main parameter list to be blanks. This converts it to a nonspecific request. This results in the system taking the same actions it would have taken if the exit had not been called except that if the request had been for a specific volume, the system will dequeue that volume serial.
• The exit can change the contents of the label that TEPMLABEL points to. We don't advise changing a reserved field in a label because IBM or a standards organization might define that field. Except for the checkpoint/restart and DDR functions, the system will treat the volume as having the changed volume label. (For those two functions the system currently reads the original labels.) If the volume serial in this changed label for this exit does not match TEPMVOL for a specific volume request, then the system will reject the volume.
• The exit can change the version of an AL volume to Version 3 or Version 4 if the system sets on bit TEPOALFRC in byte TEPOFLAG2. The system sets this bit on only if all of the following are true:
  1. it is during OPEN
  2. the OPEN option is OUTPUT or OUTIN
  3. the DD does not have DISP=MOD
  4. the file sequence number is 1
  5. the DD statement has AL coded on the LABEL parameter
  To change the version, the exit sets on TEPOEXFRC in TEPOFLAG2 and changes the eightieth byte in the area that TEPMLABEL points to be the desired version level(3 or 4) .
• The exit can change the label type of the mounted volume to unlabeled by changing the first four bytes of the area to which TEPMLABEL points. If the exit changes the area from standard labeled or non-standard labeled to unlabeled, then the system will not process existing labels. This prevents testing the expiration date, testing for data set password protection, testing the ISO/ANSI access code (ACCODE) and testing whether the volume is a checkpoint volume.

  Do not change this area to indicate the tape has SL or AL labels unless the tape actually does have that type of label.

• The exit can change TEPMVSEQ in the main parameter list. When a valid volume sequence is returned (for example, not exceeding the specific volume count in the JFCB), the system demounts the current volume and issues a mount request for the volume serial associated with the exit-supplied volume sequence.
• The exit can supply a volume serial number when processing non-SMS or SMS MTL (Manual Tape Library), nonspecific scratch NL/BLP output. The exit can also supply a volume serial number when processing SMS MTL nonspecific scratch SL/SL output when an NL volume is mounted. This will result in the system using the exit supplied volume serial number instead of generating an LNUMBER, or instead of issuing IEC519I during SMS MTL processing for a nonspecific scratch SL/AL volume when an NL volume is mounted. Prior to returning with RC00, the exit must supply a volume serial number in TEPMVOL in the main parameter list and set bit TEPMNEWLAB in byte TEPMFLAG6. Just as when an LNUMBER is generated, the system will continue to process as a nonspecific volume request.
  Note: For SMS MTL, when the VOLM (Volume Mount Exit) Tape Installation Exit does not supply a volume serial, IEC519A is issued requesting the operator to reply with the external volume serial.
• If the exit was called for volume security, then TEPOSAFRC is to replace the SAF return code. The exit might have changed it to a valid SAF return code.
• When TAPEAUTHF1=YES is set, TEPODSNF1 and TEPODS1FS are used by O/C/EOV to check authority to the first file on the volume. Refer to Table 1 for field details.

If the call was for the volume security function and the bit TEPOABEND is also set, the system abends the job.