[PATCH v5 12/15] vdpa: Adapt vhost_vdpa_get_vring_base to SVQ

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

This is needed to achieve migration, so the destination can restore its
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.

This is ok for networking, but other kinds of devices might have
problems with these retransmissions.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 8630d624f6..69a4bfd0d4 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1143,8 +1143,25 @@ static int vhost_vdpa_set_vring_base(struct vhost_dev *dev,
 static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
                                        struct vhost_vring_state *ring)
 {
+    struct vhost_vdpa *v = dev->opaque;
     int ret;
 
+    if (v->shadow_vqs_enabled) {
+        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs,
+                                                      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.
+         */
+        ring->num = svq->last_used_idx;
+        return 0;
+    }
+
     ret = vhost_vdpa_call(dev, VHOST_GET_VRING_BASE, ring);
     trace_vhost_vdpa_get_vring_base(dev, ring->index, ring->num);
     return ret;
-- 
2.27.0