Open call discussion

The I/O exit may receive multiple consecutive open calls, for various reasons internal to Z Data Tools. If the exit receives at least one open call, then the exit will receive at least one close call.

The open function code means the exit is being called immediately after a "real" file open. Additional information is now available (compared to what was available at initialization). The exit should:
  • Decide whether to continue processing the data set. (See Initialization call discussion.)
  • Set the MAXL (maximum data length) field in the I/O exit control block. There is no need to change this value if the record length is not to be changed by the exit.
  • Set the estimated raw data set size, as a percentage of the original. For example, setting the estimated raw data set size to:
    Indicates that an unencrypted data set is 50% of the encrypted data.
    Indicates that an unencrypted data set will be the same size as the encrypted data set.
    Indicates that the unencrypted data set will be twice the size of the encrypted data set (for example, as a result of decompression).
    This allows Z Data Tools to estimate the amount of in-memory storage that will be required. The sample exits in HFM.SHFMSAM1 use a setting of 200.