When creating or processing a data set with user labels, you can develop control totals for each volume of the data set and store this information in your user labels. For example, a control total that was accumulated as the data set was created can be stored in your user label and later compared with a total accumulated during processing of the volume. User totaling helps you by synchronizing the control data you create with records physically written on a volume. For an output data set without user labels, you can also develop a control total that is available to your EOV routine.

User totaling is ignored for extended format data sets and HFS data sets.

To request user totaling, you must specify OPTCD=T in the DCB macro instruction or in the DCB parameter of the DD statement. The area in which you collect the control data (the user totaling area) must be identified to the control program by an entry of X'0A' in the DCB exit list. OPTCD=T cannot be specified for SYSIN or SYSOUT data sets.

The user totaling area, an area in storage that you provide, must begin on a halfword boundary and be large enough to contain your accumulated data plus a 2 byte length field. The length field must be the first 2 bytes of the area and specify the length of the complete area. A data set for which you have specified user totaling (OPTCD=T) will not be opened if either the totaling area length or the address in the exit list is 0, or if there is no X'0A' entry in the exit list.

The control program establishes a user totaling save area, where the control program preserves an image of your totaling area, when an I/O operation is scheduled. When the output user label exits are taken, the address of the save area entry (user totaling image area) corresponding to the last record physically written on a volume is passed to you in the fourth entry of the user label parameter list. (This parameter list is described in Open/Close/EOV Standard User Label Exit.) When an EOV exit is taken for an output data set and user totaling has been specified, the address of the user totaling image area is in register 0.

When using user totaling for an output data set, that is, when creating the data set, you must update your control data in your totaling area before issuing a PUT or a WRITE macro. The control program places an image of your totaling area in the user totaling save area when an I/O operation is scheduled. A pointer to the save area entry (user totaling image area) corresponding to the last record physically written on the volume is passed to you in your label processing routine. Thus you can include the control total in your user labels.

When subsequently using this data set for input, you can collect the same information as you read each record and compare this total with the one previously stored in the user trailer label. If you have stored the total from the preceding volume in the user header label of the current volume, you can process each volume of a multivolume data set independently and still maintain this system of control.

When variable-length records are specified with the totaling function for user labels, special considerations are necessary. Because the control program determines if a variable-length record fits in a buffer after a PUT or a WRITE is issued, the total you have accumulated can include one more record than is really written on the volume. For variable-length spanned records, the accumulated total includes the control data from the volume-spanning record although only a segment of the record is on that volume. However, when you process such a data set, the volume-spanning record or the first record on the next volume will not be available to you until after the volume switch and user label processing are completed. Thus the totaling information in the user label cannot agree with that developed during processing of the volume.

One way you can resolve this situation is to maintain, when you are creating a data set, control data about each of the last two records and include both totals in your user labels. Then the total related to the last complete record on the volume and the volume-spanning record or the first record on the next volume would be available to your user label routines. During subsequent processing of the data set, your user label routines can determine if there is agreement between the generated information and one of the two totals previously saved.

When the totaling function for user labels is selected with DASD devices and secondary space is specified, the total accumulated can be one less than the actual written.