packetdrill: add test of tcp window clamp socket option

Modifies a test of TCP_WINDOW_CLAMP, including lowering, raising, and lowering again the clamp while the connection is in progress to add a test of brief lowering before raising. Requires a patch to tcp_set_window_clamp discussed as "tcp: enable mid stream window clamp". Signed-off-by: Neil Spring <[email protected]>
google · Aug 25, 2021 · 0d97599 · 0d97599
1 parent b5ec022
commit 0d97599
Showing 1 changed file with 44 additions and 2 deletions.
diff --git a/gtests/net/tcp/window_clamp/clamp-window-takes-effect.pkt b/gtests/net/tcp/window_clamp/clamp-window-takes-effect.pkt
@@ -68,6 +68,48 @@
    // Read to clear the receive buffer, will not raise the window.
   +.01 read(4, ..., 129000) = 128000
 
-   // Small data, just to check that the clamp remains.
+   // Raise briefly and lower the clamp to ensure the last write takes effect.
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [1280000], 4) = 0
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [128000], 4) = 0
+
+   // Small data, just to check that the clamp was raised; the increase
+   // opens in proportion to the amount of data sent to avoid epic burst
   +.01 < . 640000:641000(1000) ack 1 win 320
-   +0 > . 1:1(0) ack 641000 win 50
+   +0 > . 1:1(0) ack 641000 win 62
+  +.01 < . 641000:643000(2000) ack 1 win 320
+   +0 > . 1:1(0) ack 643000 win 78
+  +.01 < . 643000:646000(3000) ack 1 win 320
+   +0 > . 1:1(0) ack 646000 win 101
+  +.01 < . 646000:704000(58000) ack 1 win 320
+   +0 > . 1:1(0) ack 704000 win 500
+
+   // Read to clear the receive buffer, will not raise the window.
+  +.01 read(4, ..., 129000) = 64000
+
+   // Lower briefly and return the clamp to ensure that the last write
+   // takes effect and that the window doesn't decrease unnecessarily.
+   // (It still increases slowly based on the volume of data received.)
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [12800], 4) = 0
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [256000], 4) = 0
+
+  +.01 < . 704000:705000(1000) ack 1 win 320
+   +0 > . 1:1(0) ack 705000 win 512
+  +.01 < . 705000:707000(2000) ack 1 win 320
+   +0 > . 1:1(0) ack 707000 win 528
+
+  +.01 < . 707000:768000(61000) ack 1 win 320
+   +0 > . 1:1(0) ack 768000 win 1000
+
+  +.01 read(4, ..., 129000) = 64000
+
+   // Repeat the transient drop, but include a small packet in between.
+   // The advertised window should return to the high value quickly,
+   // since the receiver never committed to a tiny window.
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [12800], 4) = 0
+  +.01 < . 768000:769000(1000) ack 1 win 320
+   +0 > . 1:1(0) ack 769000 win 997
+
+   +0 setsockopt(4, IPPROTO_TCP, TCP_WINDOW_CLAMP, [256000], 4) = 0
+  +.01 < . 769000:770000(1000) ack 1 win 320
+   +0 > . 1:1(0) ack 770000 win 1000
+