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

[Markus Armbruster <armbru@redhat.com>]

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.

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.