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

[Richard W.M. Jones]

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.

Rich.

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