This patch adds a selftest to create id 0 subflow. Pass id 0 to the
helper userspace_pm_add_sf() to create id 0 subflow. chk_mptcp_info
shows one subflow but chk_subflows_total shows two subflows in each
namespace.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 .../testing/selftests/net/mptcp/mptcp_join.sh | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 662800437a38..2d5815ce9095 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -3462,6 +3462,25 @@ userspace_tests()
 		wait $tests_pid
 	fi
 
+	# userspace pm create id 0 subflow
+	if reset_with_events "userspace pm create id 0 subflow" &&
+	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
+		set_userspace_pm $ns2
+		pm_nl_set_limits $ns1 0 1
+		speed=10 \
+			run_tests $ns1 $ns2 10.0.1.1 &
+		local tests_pid=$!
+		wait_mpj $ns2
+		chk_mptcp_info subflows 0 subflows 0
+		chk_subflows_total 1 1
+		userspace_pm_add_sf $ns2 10.0.3.2 0
+		chk_join_nr 1 1 1
+		chk_mptcp_info subflows 1 subflows 1
+		chk_subflows_total 2 2
+		kill_events_pids
+		wait $tests_pid
+	fi
+
 	# userspace pm remove id 0 subflow
 	if reset_with_events "userspace pm remove id 0 subflow" &&
 	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
-- 
2.35.3