[PATCH v2 2/2] selftests/tc-testing: Add DualPI2 GSO backlog accounting test

[Xingquan Liu <b1n@b1n.io>]

Add a regression test for DualPI2 GSO backlog accounting when it is
used as a child qdisc of QFQ.

The test sends one UDP GSO datagram through a QFQ class with DualPI2 as
the leaf qdisc. DualPI2 splits the skb into two segments. After the
traffic drains, both QFQ and DualPI2 must report zero backlog and zero
qlen.

On kernels with the broken accounting, QFQ can keep a stale non-zero
qlen after all real packets have been dequeued.

Signed-off-by: Xingquan Liu <b1n@b1n.io>
---
 .../tc-testing/tc-tests/qdiscs/dualpi2.json   | 44 +++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/dualpi2.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/dualpi2.json
index cd1f2ee8f354..ffd6fd5ba8f7 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/dualpi2.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/dualpi2.json
@@ -250,5 +250,49 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "891f",
+        "name": "Verify DualPI2 GSO backlog accounting with QFQ parent",
+        "category": [
+            "qdisc",
+            "dualpi2",
+            "qfq",
+            "gso"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link set dev $DUMMY up || true",
+            "$IP addr add 10.10.10.10/24 dev $DUMMY || true",
+            "$TC qdisc add dev $DUMMY root handle 1: qfq",
+            "$TC class add dev $DUMMY parent 1: classid 1:1 qfq weight 1 maxpkt 4096",
+            "$TC qdisc add dev $DUMMY parent 1:1 handle 2: dualpi2",
+            "$TC filter add dev $DUMMY parent 1: matchall classid 1:1"
+        ],
+        "cmdUnderTest": "python3 -c 'import socket,struct; SOL_UDP=getattr(socket,\"SOL_UDP\",socket.IPPROTO_UDP); UDP_SEGMENT=getattr(socket,\"UDP_SEGMENT\",103); s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM); s.bind((\"10.10.10.10\",0)); p=b\"X\"*2400; n=s.sendmsg([p],[(SOL_UDP,UDP_SEGMENT,struct.pack(\"=H\",1200))],0,(\"10.10.10.1\",9000)); raise SystemExit(n != len(p))'",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -j -s qdisc ls dev $DUMMY",
+        "matchJSON": [
+            {
+                "kind": "qfq",
+                "handle": "1:",
+                "packets": 2,
+                "backlog": 0,
+                "qlen": 0
+            },
+            {
+                "kind": "dualpi2",
+                "handle": "2:",
+                "packets": 2,
+                "backlog": 0,
+                "qlen": 0
+            }
+        ],
+        "teardown": [
+            "$TC qdisc del dev $DUMMY root",
+            "$IP addr del 10.10.10.10/24 dev $DUMMY || true"
+        ]
     }
 ]
-- 
Xingquan Liu