MPTCP protocol supports having subflows in both IPv4 and IPv6. In Linux,
it is possible to have that if the MPTCP socket has been created with
AF_INET6 family without the IPV6_V6ONLY option.

Here, a new IPv4 subflow is being added to the initial IPv6 connection,
then being removed using Netlink commands.

Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
 .../selftests/net/mptcp/userspace_pm.sh       | 47 +++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/userspace_pm.sh b/tools/testing/selftests/net/mptcp/userspace_pm.sh
index a29deb9fa024..ab2d581f28a1 100755
--- a/tools/testing/selftests/net/mptcp/userspace_pm.sh
+++ b/tools/testing/selftests/net/mptcp/userspace_pm.sh
@@ -752,6 +752,52 @@ test_subflows()
 	   "$server4_token" > /dev/null 2>&1
 }
 
+test_subflows_v4_v6_mix()
+{
+	# Attempt to add a listener at 10.0.2.1:<subflow-port>
+	ip netns exec "$ns1" ./pm_nl_ctl listen 10.0.2.1\
+	   $app6_port > /dev/null 2>&1 &
+	local listener_pid=$!
+
+	# ADD_ADDR4 from server to client machine reusing the subflow port on
+	# the established v6 connection
+	:>"$client_evts"
+	ip netns exec "$ns1" ./pm_nl_ctl ann 10.0.2.1 token "$server6_token" id\
+	   $server_addr_id dev ns1eth2 > /dev/null 2>&1
+	stdbuf -o0 -e0 printf "ADD_ADDR4 id:%d 10.0.2.1 (ns1) => ns2, reuse port\t\t" $server_addr_id
+	sleep 0.5
+	verify_announce_event "$client_evts" "$ANNOUNCED" "$client6_token" "10.0.2.1"\
+			      "$server_addr_id" "$app6_port"
+
+	# CREATE_SUBFLOW from client to server machine
+	:>"$client_evts"
+	ip netns exec "$ns2" ./pm_nl_ctl csf lip 10.0.2.2 lid 23 rip 10.0.2.1 rport\
+	   $app6_port token "$client6_token" > /dev/null 2>&1
+	sleep 0.5
+	verify_subflow_events "$client_evts" "$SUB_ESTABLISHED" "$client6_token"\
+			      "$AF_INET" "10.0.2.2" "10.0.2.1" "$app6_port" "23"\
+			      "$server_addr_id" "ns2" "ns1"
+
+	# Delete the listener from the server ns, if one was created
+	kill_wait $listener_pid
+
+	sport=$(sed --unbuffered -n 's/.*\(sport:\)\([[:digit:]]*\).*$/\2/p;q' "$client_evts")
+
+	# DESTROY_SUBFLOW from client to server machine
+	:>"$client_evts"
+	ip netns exec "$ns2" ./pm_nl_ctl dsf lip 10.0.2.2 lport "$sport" rip 10.0.2.1 rport\
+	   $app6_port token "$client6_token" > /dev/null 2>&1
+	sleep 0.5
+	verify_subflow_events "$client_evts" "$SUB_CLOSED" "$client6_token" \
+			      "$AF_INET" "10.0.2.2" "10.0.2.1" "$app6_port" "23"\
+			      "$server_addr_id" "ns2" "ns1"
+
+	# RM_ADDR from server to client machine
+	ip netns exec "$ns1" ./pm_nl_ctl rem id $server_addr_id token\
+	   "$server6_token" > /dev/null 2>&1
+	sleep 0.5
+}
+
 test_prio()
 {
 	local count
@@ -861,6 +907,7 @@ make_connection "v6"
 test_announce
 test_remove
 test_subflows
+test_subflows_v4_v6_mix
 test_prio
 test_listener
 
-- 
2.37.2