Re: Intended purpose of virtio-rng's QOM link "rng"?

[Michael S. Tsirkin]

On Mon, Jul 20, 2020 at 05:07:08PM +0200, Markus Armbruster wrote:
> What is the intended purpose of object_property_set_link() in
> 
>     static void virtio_rng_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
>     {
>         VirtIORngPCI *vrng = VIRTIO_RNG_PCI(vpci_dev);
>         DeviceState *vdev = DEVICE(&vrng->vdev);
> 
>         if (!qdev_realize(vdev, BUS(&vpci_dev->bus), errp)) {
>             return;
>         }
> 
>         object_property_set_link(OBJECT(vrng), "rng", 
> OBJECT(vrng->vdev.conf.rng),
>                                  NULL);
>     }
> 
> ?
> 
> I'm asking because the function *always* fails.  I believe it's been
> failing for years.
> 
> Similar code in the CCW buddy.  Also virtio-crypto-pci and
> virtio-crypto-ccw link "cryptodev".
> 
> I tried moving it before qdev_realize(), where it doesn't fail.  But
> then *I* fail, namely at finding any effect in QOM.

I suspect that's because there's already a link with that name
created by virtio core. Is that right?

> If it's really useless, I'll send a patch to drop it.
> 
> If it has a use, tell me more, so I can test my patch to move it.