vhost: add vhost_svq_push_elem

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

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 8314405e01..1669b1fcd1 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -428,6 +428,22 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
     return g_steal_pointer(&svq->desc_state[used_elem.id].elem);
 }
 
+/**
+ * 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)
 {