[PATCH net-next 5/7] selftests/net: packetdrill: add TCP_WINDOW_CLAMP test

[Simon Baatz via B4 Relay]

From: Simon Baatz <gmbnomis@xxxxxxxxx>

Add a packetdrill test to verify that the socket option
TCP_WINDOW_CLAMP can be set to a large value on a listening socket,
but is clamped on an established socket to the maximum representable
advertised window.

Signed-off-by: Simon Baatz <gmbnomis@xxxxxxxxx>
---
 .../net/packetdrill/tcp_rcv_sockopt_wnd_clamp.pkt  | 28 ++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_sockopt_wnd_clamp.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_sockopt_wnd_clamp.pkt
new file mode 100644
index 0000000000000..d7203f2893c3f
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_sockopt_wnd_clamp.pkt
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Verify that TCP_WINDOW_CLAMP can be set to a high value on a LISTEN socket, but,
+// in an established connection, the value is clamped to the maximum representable
+// advertised window.
+--mss=1000
+
+`./defaults.sh`
+
+// Initialize connection
+    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+   +0 setsockopt(3, SOL_SOCKET, SO_RCVBUF, [256000], 4) = 0
+   +0 setsockopt(3, IPPROTO_TCP, 10, [255999], 4) = 0  // TCP_WINDOW_CLAMP == 10
+   +0 getsockopt(3, IPPROTO_TCP, 10, [255999], [4]) = 0
+   +0 bind(3, ..., ...) = 0
+   +0 listen(3, 1) = 0
+
+   +0 < S 0:0(0) win 32792
+   +0 > S. 0:0(0) ack 1 win 65535 <mss 1460>
+   +0 < . 1:1(0) ack 1 win 32792
+
+   +0 accept(3, ..., ...) = 4
+
+   +0 getsockopt(4, IPPROTO_TCP, 10, [65535], [4]) = 0
+   +0 setsockopt(4, IPPROTO_TCP, 10, [255999], 4) = 0
+   +0 getsockopt(4, IPPROTO_TCP, 10, [65535], [4]) = 0
+   +0 getsockopt(3, IPPROTO_TCP, 10, [255999], [4]) = 0

-- 
2.53.0