dm/VBS-U: implement write callback of notify cfg

virtio_notify_cfg_write is called when guest driver performs virtqueue
kick by writing the notificaiton register of the virtqueue.

Signed-off-by: Jian Jun Chen <jian.jun.chen@intel.com>
Reviewed-by: Hao Li <hao.l.li@intel.com>
Reviewed-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: chejianj

devicemodel/hw/pci/virtio/virtio.c

@@ -1340,7 +1340,31 @@ static void
 virtio_notify_cfg_write(struct pci_vdev *dev, uint64_t offset, int size,
 			uint64_t value)
 {
-	/* TODO: to be implemented */
+	struct virtio_base *base = dev->arg;
+	struct virtio_vq_info *vq;
+	struct virtio_ops *vops;
+	const char *name;
+	uint64_t idx;
+
+	idx = offset / VIRTIO_MODERN_NOTIFY_OFF_MULT;
+	vops = base->vops;
+	name = vops->name;
+
+	if (idx >= vops->nvq) {
+		fprintf(stderr,
+			"%s: queue %lu notify out of range\r\n", name, idx);
+		return;
+	}
+
+	vq = &base->queues[idx];
+	if (vq->notify)
+		(*vq->notify)(DEV_STRUCT(base), vq);
+	else if (vops->qnotify)
+		(*vops->qnotify)(DEV_STRUCT(base), vq);
+	else
+		fprintf(stderr,
+			"%s: qnotify queue %lu: missing vq/vops notify\r\n",
+			name, idx);
 }
 
 static uint32_t