To use an EXTFH interface, you must make a library available to the runtime that implements an EXTFH-compatible function and include all the necessary support libraries.
Use the following procedures to make the libraries available:
We recommend that you set the A_EXTFH runtime configuration variable to dynamically load the EXTFH library or use other A_EXTFH configuration variables to specify different libraries for specific file types.
Regardless of what method you use, you also need to set at least one of the file system configuration variables to access files through the EXTFH interface.