On Mon, 4 Oct 2021 16:01:12 -0400
"Michael S. Tsirkin" [off-list ref] wrote:

quoted

Ok, so what about something like

"If FEATURES_OK is not set, the driver MAY change the set of features it
accepts."

in the device initialization section?  

Maybe "as long as". However Halil implied that some features are not
turned off properly if that happens. Halil could you pls provide
some examples?

static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
{
...
    if (virtio_has_feature(features, VIRTIO_NET_F_STANDBY)) {
        qapi_event_send_failover_negotiated(n->netclient_name);
        qatomic_set(&n->failover_primary_hidden, false);
        failover_add_primary(n, &err);
        if (err) {
            warn_report_err(err);
        }
    }
}

This is probably the only one in QEMU. Back then I stopped looking
after the first hit.

Regards,
Halil