Re: [Libguestfs] [PATCH libnbd 1/7] api: Add semi-private function for freeing persistent data.

We then have the design question of whether to make an OClosure type, where C has two functions nbd_aio_pread and nbd_aio_pread_callback for convenience, but where other languages have only a single nbd.aio_pread where the callback parameter is optional (the Closure type for pread_structured chunk and for block_status extent will still be mandatory; it is only the completion callback that is currently causing us twice the API because we are treating it as pseudo-optional). Or maybe we just require C clients of nbd_aio_pread to always provide parameters for callbacks, but document that the completion callback and free callback pointers may be NULL.