Writing a Custom File Handler

When writing a custom file handler you must ensure that it:

Note: For concatenated files, custom file handlers that use DYNREDIR are called for each part of the concatenated file. In such cases, the custom file handler is called using the original unmapped name. A file handler that uses DYNREDIR must handle the opening and closing of each individual file that creates the concatenated file.

The final CLOSE operation is called with the initial file handle that was returned by the first OPEN operation.