Index: lib_compat_help.c
===================================================================
--- lib_compat_help.c	(revision 34379)
+++ lib_compat_help.c	(revision 34380)
@@ -6,6 +6,7 @@
 #include "pstk_help.c"
 #include "subc_help.c"
 #include "elem_rot.c"
+#include "route_style.c"
 
 int pplg_check_ver_lib_compat_help(int ver_needed) { return 0; }
 
Index: route_style.c
===================================================================
--- route_style.c	(nonexistent)
+++ route_style.c	(revision 34380)
@@ -0,0 +1,55 @@
+/*
+ *                            COPYRIGHT
+ *
+ *  pcb-rnd, interactive printed circuit board design
+ *  Copyright (C) 2021 Tibor 'Igor2' Palinkas
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ *  Contact:
+ *    Project page: http://repo.hu/projects/pcb-rnd
+ *    lead developer: http://repo.hu/projects/pcb-rnd/contact.html
+ *    mailing list: pcb-rnd (at) list.repo.hu (send "subscribe")
+ */
+
+
+int pcb_compat_route_style_via_save(pcb_data_t *data, const pcb_route_style_t *rst, rnd_coord_t *drill_dia, rnd_coord_t *pad_dia, rnd_coord_t *mask)
+{
+	/* load defaults */
+	*drill_dia = RND_MM_TO_COORD(0.42);
+	*pad_dia = RND_MM_TO_COORD(4.2);
+	*mask = 0;
+
+	if (rst->via_proto_set) {
+		pcb_pstk_compshape_t cshape;
+		rnd_bool plated;
+		pcb_pstk_proto_t *proto = pcb_pstk_get_proto_(data, rst->via_proto);
+
+		if ((proto != NULL) && (proto->tr.used > 0)) {
+			if (pcb_pstk_export_compat_proto(proto, drill_dia, pad_dia, mask, &cshape, &plated)) {
+				if ((*drill_dia <= 0) || !plated || (*mask > 0) || (cshape != PCB_PSTK_COMPAT_ROUND))
+					pcb_io_incompat_save(data, NULL, "route-style", "Route style's via padstack proto is too complex for old via description", "Use a simpler via style: copper shapes only, on all copper layers, all circle and of the same size, plus a plated round hole - gEDA/pcb can't handle anything more complex.");
+			}
+			else
+				return pcb_io_incompat_save(data, NULL, "route-style", "Failed to convert route style's via padstack proto to old via description", "Use a simpler via style: copper shapes only, on all copper layers, all circle and of the same size, plus a plated round hole - gEDA/pcb can't handle anything more complex.");
+		}
+		else
+			return pcb_io_incompat_save(data, NULL, "route-style", "Invalid route style via prototype (does not exist)", "old gEDA/PCB format requires a via geometry - exporting a dummy one");
+	}
+	else
+		return pcb_io_incompat_save(data, NULL, "route-style", "Invalid route style: no via prototype", "old gEDA/PCB format requires a via geometry - exporting a dummy one");
+
+	return 0;
+}
Index: route_style.h
===================================================================
--- route_style.h	(nonexistent)
+++ route_style.h	(revision 34380)
@@ -0,0 +1,5 @@
+/*** This API should be used only by io_pcb and io_lihata ***/
+
+/* For IO code: attempt to convert via padstack proto of a route style into old
+   geda/pcb route style description. Generates IO errors on failure. */
+int pcb_compat_route_style_via_save(pcb_data_t *data, const pcb_route_style_t *rst, rnd_coord_t *drill_dia, rnd_coord_t *pad_dia, rnd_coord_t *mask);