Connect your code to onpload at run time
When onpload determines that a custom driver is required to read or write data for a given record format, it calls the function pl_get_user_method().
The pl_get_user_method() function returns the function that the loader should call to perform initial driver configuration before any I/O activity is started. The function that you specify should be a function that you are supplying in your driver. This function should not do any other initialization. The example in the previous section illustrates the coding technique for this initial connection of your driver to onpload.