vhost: introduce new VhostOps vhost_vq_get_addr

This patch introduces new VhostOps vhost_vq_get_addr_op callback to get
the vring addr from the backend

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20200701145538.22333-9-lulu@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

include/hw/virtio/vhost-backend.h

@@ -34,6 +34,7 @@ struct vhost_vring_state;
 struct vhost_vring_addr;
 struct vhost_scsi_target;
 struct vhost_iotlb_msg;
+struct vhost_virtqueue;
 
 typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
 typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
@@ -113,6 +114,10 @@ typedef int (*vhost_set_inflight_fd_op)(struct vhost_dev *dev,
                                         struct vhost_inflight *inflight);
 
 typedef int (*vhost_dev_start_op)(struct vhost_dev *dev, bool started);
+
+typedef int (*vhost_vq_get_addr_op)(struct vhost_dev *dev,
+                    struct vhost_vring_addr *addr,
+                    struct vhost_virtqueue *vq);
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_backend_init vhost_backend_init;
@@ -154,6 +159,7 @@ typedef struct VhostOps {
     vhost_get_inflight_fd_op vhost_get_inflight_fd;
     vhost_set_inflight_fd_op vhost_set_inflight_fd;
     vhost_dev_start_op vhost_dev_start;
+    vhost_vq_get_addr_op  vhost_vq_get_addr;
 } VhostOps;
 
 extern const VhostOps user_ops;