selftests: forwarding: Add IP-in-IP GRE flat topology test

Add a test that checks IP-in-IP GRE tunneling and MTU change of tunnel,
based on flat topology described in file ipip_lib.sh.

Signed-off-by: Nir Dotan <nird@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/ipip_flat_gre.sh

@@ -0,0 +1,63 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Test IP-in-IP GRE tunnel without key.
+# This test uses flat topology for IP tunneling tests. See ipip_lib.sh for more
+# details.
+
+ALL_TESTS="gre_flat4 gre_mtu_change"
+
+NUM_NETIFS=6
+source lib.sh
+source ipip_lib.sh
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	ol1=${NETIFS[p2]}
+
+	ul1=${NETIFS[p3]}
+	ul2=${NETIFS[p4]}
+
+	ol2=${NETIFS[p5]}
+	h2=${NETIFS[p6]}
+
+	forwarding_enable
+	vrf_prepare
+	h1_create
+	h2_create
+	sw1_flat_create gre $ol1 $ul1
+	sw2_flat_create gre $ol2 $ul2
+}
+
+gre_flat4()
+{
+	RET=0
+
+	ping_test $h1 192.0.2.18 " gre flat"
+}
+
+gre_mtu_change()
+{
+	test_mtu_change gre
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	sw2_flat_destroy $ol2 $ul2
+	sw1_flat_destroy $ol1 $ul1
+	h2_destroy
+	h1_destroy
+	vrf_cleanup
+	forwarding_restore
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+tests_run
+
+exit $EXIT_STATUS