Read and Write call discussion

In this section:

The I/O exit control block field "open mode" refers to the data set open operation, therefore "input" means open for input, and "output" means open for output.
References in I/O exit control block fields to "current input record" refer to the data in the input buffers provided by Z Data Tools to the I/O exit. Similarly, references to "current output record" refer to the data in the output buffers.

Processing flow for read and write function codes:

During a read operation, Z Data Tools reads a record from a data set and places it in the I/O exit current input record. Z Data Tools then calls the exit with a read function code. The exit should then copy the current input record to the current output record buffer, performing any required processing. On return from the exit, Z Data Tools uses the processed current output record from the exit.
During a write operation, Z Data Tools takes an in-memory record and places it into the I/O exit current input record. The exit should then copy the current input record to the current output record buffer, performing any required processing. On return from the exit, Z Data Tools writes the processed current output record from the exit to DASD.