[RFC v3 09/29] vhost: Avoid re-set masked notifier in shadow vq

["Eugenio Pérez" <eperezma@redhat.com>]

Since all the shadow virtqueue device is done in software, we can avoid
the write syscall.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 7d76e271a5..c22acb4605 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -35,6 +35,9 @@ typedef struct VhostShadowVirtqueue {
     /* (Possible) masked notifier */
     struct {
         EventNotifier *n;
+
+        /* Avoid re-sending signals */
+        bool signaled;
     } masked_notifier;
 
     /* Virtio queue shadowing */
@@ -70,7 +73,8 @@ static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
         unsigned n = virtio_get_queue_index(svq->vq);
         virtio_queue_invalidate_signalled_used(svq->vdev, n);
         virtio_notify_irqfd(svq->vdev, svq->vq);
-    } else {
+    } else if (!svq->masked_notifier.signaled) {
+        svq->masked_notifier.signaled = true;
         event_notifier_set(svq->masked_notifier.n);
     }
 }
@@ -93,6 +97,7 @@ static void vhost_shadow_vq_handle_call(EventNotifier *n)
  */
 void vhost_shadow_vq_mask(VhostShadowVirtqueue *svq, EventNotifier *masked)
 {
+    svq->masked_notifier.signaled = false;
     svq->masked_notifier.n = masked;
 }
 
-- 
2.27.0