[PATCH 05/31] vhost: Add Shadow VirtQueue kick forwarding capabilities

[Eugenio Pérez]

At this mode no buffer forwarding will be performed in SVQ mode: Qemu
will just forward the guest's kicks to the device.

Also, host notifiers must be disabled at SVQ start, and they will not
start if SVQ has been enabled when the device is stopped. This will be
addressed in next patches.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  2 ++
 hw/virtio/vhost-shadow-virtqueue.c | 27 ++++++++++++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
b/hw/virtio/vhost-shadow-virtqueue.h
index a56ecfc09d..4c583a9171 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -19,6 +19,8 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int 
svq_kick_fd);
 const EventNotifier *vhost_svq_get_dev_kick_notifier(
                                               const VhostShadowVirtqueue *svq);
 
+void vhost_svq_stop(VhostShadowVirtqueue *svq);
+
 VhostShadowVirtqueue *vhost_svq_new(void);
 
 void vhost_svq_free(VhostShadowVirtqueue *vq);
diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
b/hw/virtio/vhost-shadow-virtqueue.c
index 21534bc94d..8991f0b3c3 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -42,11 +42,26 @@ const EventNotifier *vhost_svq_get_dev_kick_notifier(
     return &svq->hdev_kick;
 }
 
+/* Forward guest notifications */
+static void vhost_handle_guest_kick(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
+                                             svq_kick);
+
+    if (unlikely(!event_notifier_test_and_clear(n))) {
+        return;
+    }
+
+    event_notifier_set(&svq->hdev_kick);
+}
+
 /**
  * Set a new file descriptor for the guest to kick SVQ and notify for avail
  *
  * @svq          The svq
- * @svq_kick_fd  The new svq kick fd
+ * @svq_kick_fd  The svq kick fd
+ *
+ * Note that SVQ will never close the old file descriptor.
  */
 void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
 {
@@ -65,12 +80,22 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, 
int svq_kick_fd)
      * need to explicitely check for them.
      */
     event_notifier_init_fd(&svq->svq_kick, svq_kick_fd);
+    event_notifier_set_handler(&svq->svq_kick, vhost_handle_guest_kick);
 
     if (!check_old || event_notifier_test_and_clear(&tmp)) {
         event_notifier_set(&svq->hdev_kick);
     }
 }
 
+/**
+ * Stop shadow virtqueue operation.
+ * @svq Shadow Virtqueue
+ */
+void vhost_svq_stop(VhostShadowVirtqueue *svq)
+{
+    event_notifier_set_handler(&svq->svq_kick, NULL);
+}
+
 /**
  * Creates vhost shadow virtqueue, and instruct vhost device to use the shadow
  * methods and file descriptors.
-- 
2.27.0