selftests: pmtu: Add pmtu_vti6_link_change_mtu test

This test checks that MTU configured from userspace is used on
link creation and changes, and that when it's not passed from
userspace, it's calculated properly from the MTU of the lower
layer.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/pmtu.sh

@@ -36,6 +36,12 @@
 #
 # - pmtu_vti6_link_add_mtu
 #	Same as above, for IPv6
+#
+# - pmtu_vti6_link_change_mtu
+#	Set up two dummy interfaces with different MTUs, create a vti6 tunnel
+#	and check that configured MTU is used on link creation and changes, and
+#	that MTU is properly calculated instead when MTU is not configured from
+#	userspace
 
 tests="
 	pmtu_vti6_exception		vti6: PMTU exceptions
@@ -43,7 +49,8 @@ tests="
 	pmtu_vti4_default_mtu		vti4: default MTU assignment
 	pmtu_vti6_default_mtu		vti6: default MTU assignment
 	pmtu_vti4_link_add_mtu		vti4: MTU setting on link creation
-	pmtu_vti6_link_add_mtu	vti6: MTU setting on link creation"
+	pmtu_vti6_link_add_mtu		vti6: MTU setting on link creation
+	pmtu_vti6_link_change_mtu	vti6: MTU changes on link changes"
 
 NS_A="ns-$(mktemp -u XXXXXX)"
 NS_B="ns-$(mktemp -u XXXXXX)"
@@ -64,6 +71,10 @@ vti6_a_addr="fd00:2::a"
 vti6_b_addr="fd00:2::b"
 vti6_mask="64"
 
+dummy6_0_addr="fc00:1000::0"
+dummy6_1_addr="fc00:1001::0"
+dummy6_mask="64"
+
 cleanup_done=1
 err_buf=
 
@@ -386,6 +397,50 @@ test_pmtu_vti6_link_add_mtu() {
 	return ${fail}
 }
 
+test_pmtu_vti6_link_change_mtu() {
+	setup namespaces || return 2
+
+	${ns_a} ip link add dummy0 mtu 1500 type dummy
+	[ $? -ne 0 ] && err "  dummy not supported" && return 2
+	${ns_a} ip link add dummy1 mtu 3000 type dummy
+	${ns_a} ip link set dummy0 up
+	${ns_a} ip link set dummy1 up
+
+	${ns_a} ip addr add ${dummy6_0_addr}/${dummy6_mask} dev dummy0
+	${ns_a} ip addr add ${dummy6_1_addr}/${dummy6_mask} dev dummy1
+
+	fail=0
+
+	# Create vti6 interface bound to device, passing MTU, check it
+	${ns_a} ip link add vti6_a mtu 1300 type vti6 remote ${dummy6_0_addr} local ${dummy6_0_addr}
+	mtu="$(link_get_mtu "${ns_a}" vti6_a)"
+	if [ ${mtu} -ne 1300 ]; then
+		err "  vti6 MTU ${mtu} doesn't match configured value 1300"
+		fail=1
+	fi
+
+	# Move to another device with different MTU, without passing MTU, check
+	# MTU is adjusted
+	echo "${ns_a} ip link set vti6_a type vti6 remote ${dummy6_1_addr} local ${dummy6_1_addr}" > /dev/kmsg
+	${ns_a} ip link set vti6_a type vti6 remote ${dummy6_1_addr} local ${dummy6_1_addr}
+	mtu="$(link_get_mtu "${ns_a}" vti6_a)"
+	if [ ${mtu} -ne $((3000 - 40)) ]; then
+		err "  vti MTU ${mtu} is not dummy MTU 3000 minus IPv6 header length"
+		fail=1
+	fi
+
+	# Move it back, passing MTU, check MTU is not overridden
+	echo "${ns_a} ip link set vti6_a mtu 1280 type vti6 remote ${dummy6_0_addr} local ${dummy6_0_addr}" > /dev/kmsg
+	${ns_a} ip link set vti6_a mtu 1280 type vti6 remote ${dummy6_0_addr} local ${dummy6_0_addr}
+	mtu="$(link_get_mtu "${ns_a}" vti6_a)"
+	if [ ${mtu} -ne 1280 ]; then
+		err "  vti6 MTU ${mtu} doesn't match configured value 1280"
+		fail=1
+	fi
+
+	return ${fail}
+}
+
 trap cleanup EXIT
 
 exitcode=0