[PATCH v3 2/2] net/tcp: add packetdrill test for FIN-WAIT-1 zero-window fix

[HaiYang Zhong]

Move the packetdrill test to the packetdrill directory and shorten
the test duration.

In the previous packetdrill test script, the long duration was due to
presenting the entire zero-window probe backoff process. The test has
been modified to only observe the first few packets to shorten the test
time while still effectively verifying the fix.

- Moved test to tools/testing/selftests/net/packetdrill/
- Reduced test duration from 360+ seconds to under 4 seconds

Signed-off-by: HaiYang Zhong <wokezhong@xxxxxxxxxxx>
---
 .../packetdrill/tcp_fin_wait1_zero_window.pkt | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt

diff --git a/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt b/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt
new file mode 100644
index 000000000000..854ede56e7dd
--- /dev/null
+++ b/tools/testing/selftests/net/packetdrill/tcp_fin_wait1_zero_window.pkt
@@ -0,0 +1,34 @@
+// Test for permanent FIN-WAIT-1 state with continuous zero-window advertisements
+// Author: HaiYang Zhong <wokezhong@xxxxxxxxxxx>
+
+
+0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
+0.000 bind(3, ..., ...) = 0
+0.000 listen(3, 1) = 0
+
+0.100 < S 0:0(0) win 65535 <mss 1460>
+0.100 > S. 0:0(0) ack 1 <mss 1460>
+0.100 < . 1:1(0) ack 1 win 65535
+0.100 accept(3, ..., ...) = 4
+
+// Send data to fill receive window
+0.200 write(4, ..., 5) = 5
+0.200 > P. 1:6(5) ack 1
+
+// Advertise zero-window
+0.200 < . 1:1(0) ack 6 win 0
+
+// Application closes connection, sends FIN (but blocked by zero window)
+0.200 close(4) = 0
+
+//Send zero-window probe packet
++0.200 > . 5:5(0) ack 1
++0.400 > . 5:5(0) ack 1
++0.800 > . 5:5(0) ack 1
+
++1.000 < . 1:1(0) ack 6 win 0
+
+// Without fix: This probe won't match - timer was reset, probe will be sent 2.600s after the previous probe
+// With fix: This probe matches - exponential backoff continues (1.600s after previous probe)
++0.600~+0.700 > . 5:5(0) ack 1
-- 
2.43.7