[PATCH RFC net-next 3/4] selftests/net: packetdrill: add tcp_rcv_wnd_shrink_allowed.pkt
From: Simon Baatz via B4 Relay <devnull+gmbnomis.gmail.com@kernel.org>
Date: 2026-02-19 23:56:04
Also in:
b4-sent, linux-doc, linux-kselftest, lkml
Subsystem:
kernel selftest framework, networking [general], the rest · Maintainers:
Shuah Khan, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Simon Baatz <redacted> This test verifies the sequence number checks using the maximum advertised window sequence number when net.ipv4.tcp_shrink_window is enabled. Signed-off-by: Simon Baatz <redacted> --- .../net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt | 35 ++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt
new file mode 100644
index 0000000000000000000000000000000000000000..8f9b689d3f6d49c3bbc26cca8e408b905af129cb
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_rcv_wnd_shrink_allowed.pkt@@ -0,0 +1,35 @@ +// SPDX-License-Identifier: GPL-2.0 + +--mss=1000 + +`./defaults.sh +sysctl -q net.ipv4.tcp_shrink_window=1 +sysctl -q net.ipv4.tcp_rmem="4096 32768 $((32*1024*1024))"` + + 0 `nstat -n` + +// Establish a connection. + +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 32792 <mss 1000,nop,wscale 7> + +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 10> + +0 < . 1:1(0) ack 1 win 257 + + +0 accept(3, ..., ...) = 4 + + +0 < P. 1:10001(10000) ack 1 win 257 + * > . 1:1(0) ack 10001 win 15 + + +0 < P. 10001:11024(1023) ack 1 win 257 + * > . 1:1(0) ack 11024 win 13 + +// Max window seq advertised 10001 + 15*1024 = 25361, last advertised: 11024 + 13*1024 = 24336 +// Segment using the max window is accepted + +0 < P. 11024:25361(14337) ack 1 win 257 + * > . 1:1(0) ack 25361 win 0 + +// Check LINUX_MIB_BEYOND_WINDOW has not been incremented + +0 `nstat -z | grep TcpExtBeyondWindow | grep -q " 0 "`
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2.52.0