selftests: forwarding: Add test for minimum and maximum MTU

Add cases to check minimum and maximum MTU which are exposed via
"ip -d link show". Test configuration and traffic. Use VLAN devices as
usually VLAN header (4 bytes) is not included in the MTU, and drivers
should configure hardware correctly to send maximum MTU payload size
in VLAN tagged packets.

$ ./min_max_mtu.sh
TEST: ping						[ OK ]
TEST: ping6						[ OK ]
TEST: Test maximum MTU configuration			[ OK ]
TEST: Test traffic, packet size is maximum MTU		[ OK ]
TEST: Test minimum MTU configuration			[ OK ]
TEST: Test traffic, packet size is minimum MTU		[ OK ]
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Link: https://lore.kernel.org/r/89de8be8989db7a97f3b39e3c9da695673e78d2e.1718275854.git.petrm@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/forwarding/Makefile

@@ -39,6 +39,7 @@ TEST_PROGS = bridge_fdb_learning_limit.sh \
 	ipip_hier_gre.sh \
 	lib_sh_test.sh \
 	local_termination.sh \
+	min_max_mtu.sh \
 	mirror_gre_bound.sh \
 	mirror_gre_bridge_1d.sh \
 	mirror_gre_bridge_1d_vlan.sh \

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

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# +--------------------+
+# | H1                 |
+# |                    |
+# |           $h1.10 + |
+# |     192.0.2.2/24 | |
+# | 2001:db8:1::2/64 | |
+# |                  | |
+# |              $h1 + |
+# |                  | |
+# +------------------|-+
+#                    |
+# +------------------|-+
+# | SW               | |
+# |            $swp1 + |
+# |                  | |
+# |         $swp1.10 + |
+# |     192.0.2.1/24   |
+# | 2001:db8:1::1/64   |
+# |                    |
+# +--------------------+
+
+ALL_TESTS="
+	ping_ipv4
+	ping_ipv6
+	max_mtu_config_test
+	max_mtu_traffic_test
+	min_mtu_config_test
+	min_mtu_traffic_test
+"
+
+NUM_NETIFS=2
+source lib.sh
+
+h1_create()
+{
+	simple_if_init $h1
+	vlan_create $h1 10 v$h1 192.0.2.2/24 2001:db8:1::2/64
+}
+
+h1_destroy()
+{
+	vlan_destroy $h1 10 192.0.2.2/24 2001:db8:1::2/64
+	simple_if_fini $h1
+}
+
+switch_create()
+{
+	ip li set dev $swp1 up
+	vlan_create $swp1 10 "" 192.0.2.1/24 2001:db8:1::1/64
+}
+
+switch_destroy()
+{
+	ip li set dev $swp1 down
+	vlan_destroy $swp1 10
+}
+
+setup_prepare()
+{
+	h1=${NETIFS[p1]}
+	swp1=${NETIFS[p2]}
+
+	vrf_prepare
+
+	h1_create
+
+	switch_create
+
+	forwarding_enable
+}
+
+cleanup()
+{
+	pre_cleanup
+
+	forwarding_restore
+
+	switch_destroy
+
+	h1_destroy
+
+	vrf_cleanup
+}
+
+ping_ipv4()
+{
+	ping_test $h1.10 192.0.2.1
+}
+
+ping_ipv6()
+{
+	ping6_test $h1.10 2001:db8:1::1
+}
+
+min_max_mtu_get_if()
+{
+	local dev=$1; shift
+	local min_max=$1; shift
+
+	ip -d -j link show $dev | jq ".[].$min_max"
+}
+
+ensure_compatible_min_max_mtu()
+{
+	local min_max=$1; shift
+
+	local mtu=$(min_max_mtu_get_if ${NETIFS[p1]} $min_max)
+	local i
+
+	for ((i = 2; i <= NUM_NETIFS; ++i)); do
+		local current_mtu=$(min_max_mtu_get_if ${NETIFS[p$i]} $min_max)
+
+		if [ $current_mtu -ne $mtu ]; then
+			return 1
+		fi
+	done
+}
+
+mtu_set_if()
+{
+	local dev=$1; shift
+	local mtu=$1; shift
+	local should_fail=${1:-0}; shift
+
+	mtu_set $dev $mtu 2>/dev/null
+	check_err_fail $should_fail $? "Set MTU $mtu for $dev"
+}
+
+mtu_set_all_if()
+{
+	local mtu=$1; shift
+	local i
+
+	for ((i = 1; i <= NUM_NETIFS; ++i)); do
+		mtu_set_if ${NETIFS[p$i]} $mtu
+		mtu_set_if ${NETIFS[p$i]}.10 $mtu
+	done
+}
+
+mtu_restore_all_if()
+{
+	local i
+
+	for ((i = 1; i <= NUM_NETIFS; ++i)); do
+		mtu_restore ${NETIFS[p$i]}.10
+		mtu_restore ${NETIFS[p$i]}
+	done
+}
+
+mtu_test_ping4()
+{
+	local mtu=$1; shift
+	local should_fail=$1; shift
+
+	# Ping adds 8 bytes for ICMP header and 20 bytes for IP header
+	local ping_headers_len=$((20 + 8))
+	local pkt_size=$((mtu - ping_headers_len))
+
+	ping_do $h1.10 192.0.2.1 "-s $pkt_size -M do"
+	check_err_fail $should_fail $? "Ping, packet size: $pkt_size"
+}
+
+mtu_test_ping6()
+{
+	local mtu=$1; shift
+	local should_fail=$1; shift
+
+	# Ping adds 8 bytes for ICMP header and 40 bytes for IPv6 header
+	local ping6_headers_len=$((40 + 8))
+	local pkt_size=$((mtu - ping6_headers_len))
+
+	ping6_do $h1.10 2001:db8:1::1 "-s $pkt_size -M do"
+	check_err_fail $should_fail $? "Ping6, packet size: $pkt_size"
+}
+
+max_mtu_config_test()
+{
+	local i
+
+	RET=0
+
+	for ((i = 1; i <= NUM_NETIFS; ++i)); do
+		local dev=${NETIFS[p$i]}
+		local max_mtu=$(min_max_mtu_get_if $dev "max_mtu")
+		local should_fail
+
+		should_fail=0
+		mtu_set_if $dev $max_mtu $should_fail
+		mtu_restore $dev
+
+		should_fail=1
+		mtu_set_if $dev $((max_mtu + 1)) $should_fail
+		mtu_restore $dev
+	done
+
+	log_test "Test maximum MTU configuration"
+}
+
+max_mtu_traffic_test()
+{
+	local should_fail
+	local max_mtu
+
+	RET=0
+
+	if ! ensure_compatible_min_max_mtu "max_mtu"; then
+		log_test_xfail "Topology has incompatible maximum MTU values"
+		return
+	fi
+
+	max_mtu=$(min_max_mtu_get_if ${NETIFS[p1]} "max_mtu")
+
+	should_fail=0
+	mtu_set_all_if $max_mtu
+	mtu_test_ping4 $max_mtu $should_fail
+	mtu_test_ping6 $max_mtu $should_fail
+	mtu_restore_all_if
+
+	should_fail=1
+	mtu_set_all_if $((max_mtu - 1))
+	mtu_test_ping4 $max_mtu $should_fail
+	mtu_test_ping6 $max_mtu $should_fail
+	mtu_restore_all_if
+
+	log_test "Test traffic, packet size is maximum MTU"
+}
+
+min_mtu_config_test()
+{
+	local i
+
+	RET=0
+
+	for ((i = 1; i <= NUM_NETIFS; ++i)); do
+		local dev=${NETIFS[p$i]}
+		local min_mtu=$(min_max_mtu_get_if $dev "min_mtu")
+		local should_fail
+
+		should_fail=0
+		mtu_set_if $dev $min_mtu $should_fail
+		mtu_restore $dev
+
+		should_fail=1
+		mtu_set_if $dev $((min_mtu - 1)) $should_fail
+		mtu_restore $dev
+	done
+
+	log_test "Test minimum MTU configuration"
+}
+
+min_mtu_traffic_test()
+{
+	local should_fail=0
+	local min_mtu
+
+	RET=0
+
+	if ! ensure_compatible_min_max_mtu "min_mtu"; then
+		log_test_xfail "Topology has incompatible minimum MTU values"
+		return
+	fi
+
+	min_mtu=$(min_max_mtu_get_if ${NETIFS[p1]} "min_mtu")
+	mtu_set_all_if $min_mtu
+	mtu_test_ping4 $min_mtu $should_fail
+	# Do not test minimum MTU with IPv6, as IPv6 requires higher MTU.
+
+	mtu_restore_all_if
+
+	log_test "Test traffic, packet size is minimum MTU"
+}
+
+trap cleanup EXIT
+
+setup_prepare
+setup_wait
+
+tests_run
+
+exit $EXIT_STATUS