DSN=addr

Supplies the address of a 44-byte area containing either zeros or a data set name. Specifying the DSN keyword causes access of an indexed VTOC by DSN order. BUFLIST is required if DSNONLY=NO is coded or the default.

DSN omitted

If you omit the DSN keyword, access of an indexed or nonindexed VTOC is by physical-sequential order. BUFLIST is required.

If the order is physical-sequential, initialize the argument field in the first buffer list entry to zero or to the argument of the DSCB. If the argument is zero (BFLEARG=00), the read begins at the start of the VTOC. You must be authorized (APF or system key) to read multiple DSCBs with a single invocation of the CVAFSEQ macro. See Initiating Physical-Sequential Access for more information.