[PATCH mptcp-net v4 5/5] selftests: mptcp: test transmission with small rcvbuf

[Gang Yan <gang.yan@linux.dev>]

From: Gang Yan <yangang@kylinos.cn>

This patch adds a test for transmission with a limited receive buffer.

Without the fixes in this set, this test fails with errors:

 # 001 4 subflows with reduced rcvbuf
 # net.ipv4.tcp_rmem = 4096 4096 4096
 #       Info: Test file (size 1024 KB) for client
 #       Info: Test file (size 1024 KB) for server
 # copyfd_io_poll: poll timed out (events: POLLIN 1, POLLOUT 0)
 # copyfd_io_poll: poll timed out (events: POLLIN 0, POLLOUT 4)
 # [FAIL] client exit code 2, server 2
 # Server ns stats (ns2-qg1Hqo)

Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 .../testing/selftests/net/mptcp/mptcp_join.sh | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index beec41f6662a..6bf7ebedfbc8 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -4417,6 +4417,25 @@ endpoint_tests()
 	fi
 }
 
+rcvbuf_tests()
+{
+	if reset "4 subflows with reduced rcvbuf"; then
+		local tcp_rmem=$(ip netns exec $ns2 sysctl -n net.ipv4.tcp_rmem)
+		ip netns exec $ns2 sysctl -w net.ipv4.tcp_rmem="4096 4096 4096"
+
+		pm_nl_set_limits $ns1 0 4
+		pm_nl_set_limits $ns2 0 4
+		pm_nl_add_endpoint $ns2 10.0.2.2 flags subflow
+		pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
+		pm_nl_add_endpoint $ns2 10.0.4.2 flags subflow
+		speed=fast test_linkfail=1024 \
+			run_tests $ns1 $ns2 10.0.1.1
+		chk_join_nr 3 3 3
+
+		ip netns exec $ns2 sysctl -w net.ipv4.tcp_rmem="$tcp_rmem"
+	fi
+}
+
 # [$1: error message]
 usage()
 {
@@ -4467,6 +4486,7 @@ all_tests_sorted=(
 	F@fail_tests
 	u@userspace_tests
 	I@endpoint_tests
+	R@rcvbuf_tests
 )
 
 all_tests_args=""
-- 
2.43.0