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

On Mon, Aug 12, 2019 at 11:00:01PM +0100, Richard W.M. Jones wrote: > On Mon, Aug 12, 2019 at 01:53:56PM -0500, Eric Blake wrote: >> 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. > > I'll try to see what OClosure (and then getting rid of the _callback > variants, adding to the non-callback variants OClosure) will look like > tomorrow. I should say that while OClosure has the possibility of solving the freeing problem for buffers and closures attached to AIO commands, and may also be a good idea to get rid of the *_callback variants, it doesn't solve the problem in general. In particular there's no way to free the debug function closure, which means it would be leaked in language bindings.