-extern struct vconn_class tcp_vconn_class;
-extern struct pvconn_class ptcp_pvconn_class;
-extern struct vconn_class unix_vconn_class;
-extern struct pvconn_class punix_pvconn_class;
+extern const struct vconn_class tcp_vconn_class;
+extern const struct pvconn_class ptcp_pvconn_class;
+extern const struct vconn_class unix_vconn_class;
+extern const struct pvconn_class punix_pvconn_class;