[Libguestfs] [PATCH libnbd] generator: Define new Closure type

[Eric Blake]

On 7/16/19 4:51 AM, Richard W.M. Jones wrote:

> 
> Note that nbd_add_close_callback is inconsistent with other closure
> types because it passes the user_data parameter after the function.
> (This is not caused by the current patch, it was already
> inconsistent).  We decided that nbd_add_close_callback should be
> manually generated and not automatically generated because it should
> only be called from C, or perhaps more accurately it is only _needed_
> from C (to support cleanup of the non-C bindings), but I don't think
> there's any reason not to automatically generate it.  If we did
> generate it, then it would be an API break because these two
> parameters would get swapped around.

I don't mind a separate patch to switch the argument order to make it
consistent, whether or not we decide to generate it (we've already
broken API since the last release due to s/notify/callback/, and we've
already had other API breaks that swapped argument order of int *exit
for consistency, so getting things consistent now is worthwhile).

As for whether to generate it (so that other languages can register a
close callback), I'm on the fence. But in the long run, having our
initial stable API with close callbacks being C only, and a later
release that adds language callbacks because it is generated, should be
upwards compatible.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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