[PATCH net-next 2/4] selftests/net: packetdrill: test tcp_base_mss on passive connections

[Yongjian Wang via B4 Relay <devnull+echoowall.gmail.com@kernel.org>]

From: Yongjian Wang <echoowall@gmail.com>

Check that a passive connection starts at tcp_base_mss with
net.ipv4.tcp_mtu_probing=2, as an active connection does.

Signed-off-by: Yongjian Wang <echoowall@gmail.com>
---
 .../net/packetdrill/tcp_mtu_probing_passive.pkt    | 27 ++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/tools/testing/selftests/net/packetdrill/tcp_mtu_probing_passive.pkt b/tools/testing/selftests/net/packetdrill/tcp_mtu_probing_passive.pkt
new file mode 100644
index 000000000..14bae144c
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_mtu_probing_passive.pkt
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+// Test that a passive connection starts at tcp_base_mss with tcp_mtu_probing=2,
+// the same way as an active connection.
+
+`./defaults.sh
+sysctl -q net.ipv4.tcp_mtu_probing=2
+sysctl -q net.ipv4.tcp_base_mss=1024
+sysctl -q net.ipv4.tcp_timestamps=0`
+
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 65535 <mss 1460,nop,nop,sackOK>
+   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+  +.1 < . 1:1(0) ack 1 win 65535
+   +0 accept(3, ..., ...) = 4
+
+// The initial window is sent with tcp_base_mss, not the peer's MSS.
+   +0 write(4, ..., 10240) = 10240
+   +0 > P. 1:2049(2048) ack 1
+   +0 > P. 2049:4097(2048) ack 1
+   +0 > P. 4097:6145(2048) ack 1
+   +0 > P. 6145:8193(2048) ack 1
+   +0 > P. 8193:10241(2048) ack 1
+  +.1 < . 1:1(0) ack 10241 win 65535

-- 
Git-157)