[PATCH 16/22] vhost: add detach SVQ operation

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

To notify the caller it needs to discard the element.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h | 11 +++++++++++
 hw/virtio/vhost-shadow-virtqueue.c | 11 ++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index cfc891e2e8..dc0059adc6 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -44,9 +44,20 @@ typedef void (*VirtQueueUsedCallback)(VhostShadowVirtqueue *svq,
                                       void *used_elem_opaque,
                                       uint32_t written);
 
+/**
+ * Detach the element from the shadow virtqueue.  SVQ needs to free it and it
+ * cannot be pushed or discarded.
+ *
+ * @elem_opaque: The element opaque
+ *
+ * Return the guest element to detach and free if any.
+ */
+typedef VirtQueueElement *(*VirtQueueDetachCallback)(void *elem_opaque);
+
 typedef struct VhostShadowVirtqueueOps {
     VirtQueueAvailCallback avail_handler;
     VirtQueueUsedCallback used_handler;
+    VirtQueueDetachCallback detach_handler;
 } VhostShadowVirtqueueOps;
 
 /* Shadow virtqueue to relay notifications */
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 78579b9e0b..626691ac4e 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -749,7 +749,16 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
 
     for (unsigned i = 0; i < svq->vring.num; ++i) {
         g_autofree VirtQueueElement *elem = NULL;
-        elem = g_steal_pointer(&svq->ring_id_maps[i].opaque);
+        void *opaque = g_steal_pointer(&svq->ring_id_maps[i].opaque);
+
+        if (!opaque) {
+            continue;
+        } else if (svq->ops) {
+            elem = svq->ops->detach_handler(opaque);
+        } else {
+            elem = opaque;
+        }
+
         if (elem) {
             virtqueue_detach_element(svq->vq, elem, 0);
         }
-- 
2.31.1