[RFC PATCH 02/12] vhost: Move SVQ queue rewind to the destination

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

Migration with SVQ already migrate the inflight descriptors, so the
destination can perform the work.

This makes easier to migrate between backends or to recover them in
vhost devices that support set in flight descriptors.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 18820498b3..4458c8d23e 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1178,7 +1178,18 @@ static int vhost_vdpa_set_vring_base(struct vhost_dev *dev,
                                        struct vhost_vring_state *ring)
 {
     struct vhost_vdpa *v = dev->opaque;
+    VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
 
+    /*
+     * vhost-vdpa devices does not support in-flight requests. Set all of them
+     * as available.
+     *
+     * TODO: This is ok for networking, but other kinds of devices might
+     * have problems with these retransmissions.
+     */
+    while (virtqueue_rewind(vq, 1)) {
+        continue;
+    }
     if (v->shadow_vqs_enabled) {
         /*
          * Device vring base was set at device start. SVQ base is handled by
@@ -1197,19 +1208,6 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
     int ret;
 
     if (v->shadow_vqs_enabled) {
-        VirtQueue *vq = virtio_get_queue(dev->vdev, ring->index);
-
-        /*
-         * Setting base as last used idx, so destination will see as available
-         * all the entries that the device did not use, including the in-flight
-         * processing ones.
-         *
-         * TODO: This is ok for networking, but other kinds of devices might
-         * have problems with these retransmissions.
-         */
-        while (virtqueue_rewind(vq, 1)) {
-            continue;
-        }
         ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
         return 0;
     }
-- 
2.31.1