On 2018年05月30日 19:42, Wei Xu wrote:

quoted

  /* This actually signals the guest, using eventfd. */
  void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
  {

@@ -2802,10 +2930,34 @@ static bool vhost_enable_notify_packed(struct vhost_dev *dev,
  				       struct vhost_virtqueue *vq)
  {
  	struct vring_desc_packed *d = vq->desc_packed + vq->avail_idx;
-	__virtio16 flags;
+	__virtio16 flags = RING_EVENT_FLAGS_ENABLE;
  	int ret;
  
-	/* FIXME: disable notification through device area */
+	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
+		return false;
+	vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;

'used_flags' was originally designed for 1.0, why should we pay attetion to it here?

Wei

It was used to recored whether or not we've disabled notification. Then 
we can avoid unnecessary userspace writes or memory barriers.

Thanks