Accessing the VTOC with DADSM Macros

You can use either DADSM or common VTOC access facility (CVAF) macros to access a VTOC and its index. (CVAF access is described in Accessing the VTOC with CVAF Macros.) The DADSM macros and tasks covered here include:

LSPACE provides information on volume size, free space on the volume, free space on the VTOC and INDEX, volume fragmentation, and VTOC status. Also provided is information on the size of the track-managed space and its free space statistics.
OBTAIN reads one or more DSCBs from the VTOC.
PARTREL releases unused space from a sequential or partitioned data set or a PDSE.
REALLOC allocates DASD space.

To read one or more DSCBs into virtual storage, use the OBTAIN and CAMLST macro instructions. Identify the DSCB to be read using the name of the data set associated with the DSCB, or the absolute track address of the DSCB. Provide a 140-byte data area in virtual storage to contain the DSCB. On a request to read multiple DSCBs specify the NUMBERDSCB= parameter on the OBTAIN or CAMLST macro and provide consecutive 140-byte return areas in virtual storage to contain this number of DSCBs. When you specify the name of the data set, an identifier (format-1, format-4, or format-8) DSCB is read into virtual storage. To read a DSCB other than a format-1, format-4, or format-8 DSCB, specify an absolute track address (see the example on page Example). Code the EADSCB=OK on the OBTAIN or CAMLST macro when your program supports DSCBs that describe data sets with format-8 and format-9 DSCBs. The extent descriptors in DSCBs for a data set described with these formats may have 28-bit cylinder track addresses. Use the TRKADDR macro or IECTRKAD service to manipulate 16-bit or 28-bit cylinder track addresses.

Restriction: You cannot use the OBTAIN macro instruction with either a SYSIN or SYSOUT data set.

To release unused space from a sequential, partitioned, or key sequenced data set or a PDSE, use the PARTREL macro instruction. Your program must be APF authorized.

Another way is to code the RLSE option on the SPACE keyword on the DD statement or the dynamic allocation equivalent. This technique does not require APF authorization. It requires that your program open the data set with the OUTPUT, EXTEND, OUTIN, OUTINX or INOUT option and the last operation before closing the data set not be a read or POINT macro."

The following macro instruction descriptions include coding examples, programming notes, and exception return code descriptions.