On 08/26/2015 08:41 AM, Markus Armbruster wrote: > Only reviewing the QAPI part. > > Yang Hongyang <yan...@cn.fujitsu.com> writes: >
> Let's make this a flat union instead, to reduce nesting, and therefore
> memory allocations and indirections. Something like
>
> { 'enum': 'NetFilterType',
> 'data': [] }
>
> { 'struct': NetFilterBase',
> 'data': {
> 'id': 'str',
> 'netdev': 'str',
> '*chain': 'str',
> 'type': 'NetFilterType'
>
> { 'union': 'NetFilter',
> 'base': 'NetFilterBase',
> 'discriminator': 'type',
> 'data': {
> }
> }
>
> I hope to reduce the notational overhead of such flat unions in the near
> future.
>
> Not sure empty unions actually work. If they don't, you can either
> squash adding members into this patch, or add a dummy member, and drop
> it when you add the real ones.
The generator handles an empty union without compilation error, but
creates C code that will always abort() if the union is passed on the
wire. I have pending patches on top of Markus' that outlaw an empty union:
[uggh: https://lists.gnu.org/archive/html/qemu-devel/ is hosed right
now, and it's harder to find messages on other archivers...]
http://thread.gmane.org/gmane.comp.emulators.qemu/356265/focus=356258
http://thread.gmane.org/gmane.comp.emulators.qemu/356265/focus=356294
so a dummy member for now is a reasonable compromise.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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