This function allows external SVQ users to return guest's available
buffers.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  2 ++
 hw/virtio/vhost-shadow-virtqueue.c | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index 91c31715d9..0fbdd69153 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -88,6 +88,8 @@ typedef struct VhostShadowVirtqueue {
 
 bool vhost_svq_valid_features(uint64_t features, Error **errp);
 
+void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
+                         const VirtQueueElement *elem, uint32_t len);
 void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
 void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd);
 void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index be64e0b85c..2fc5789b73 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -410,6 +410,22 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
     return g_steal_pointer(&svq->ring_id_maps[used_elem.id]);
 }
 
+/**
+ * Push an element to SVQ, returning it to the guest.
+ */
+void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
+                         const VirtQueueElement *elem, uint32_t len)
+{
+    virtqueue_push(svq->vq, elem, len);
+    if (svq->next_guest_avail_elem) {
+        /*
+         * Avail ring was full when vhost_svq_flush was called, so it's a
+         * good moment to make more descriptors available if possible.
+         */
+        vhost_handle_guest_kick(svq);
+    }
+}
+
 static void vhost_svq_flush(VhostShadowVirtqueue *svq,
                             bool check_for_avail_queue)
 {
-- 
2.31.1