selftests/tc-testing: sfq: test that kernel rejects limit of 1

Add test to check that the kernel rejects a configuration with the
limit set to 1.

Signed-off-by: Octavian Purdila <tavip@google.com>
Link: https://patch.msgid.link/20241204030520.2084663-3-tavip@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/tc-testing/scripts/sfq_rejects_limit_1.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Script that checks that SFQ rejects a limit of 1 at the kernel
+# level. We can't use iproute2's tc because it does not accept a limit
+# of 1.
+
+import sys
+import os
+
+from pyroute2 import IPRoute
+from pyroute2.netlink.exceptions import NetlinkError
+
+ip = IPRoute()
+ifidx = ip.link_lookup(ifname=sys.argv[1])
+
+try:
+    ip.tc('add', 'sfq', ifidx, limit=1)
+    sys.exit(1)
+except NetlinkError:
+    sys.exit(0)

tools/testing/selftests/tc-testing/tc-tests/qdiscs/sfq.json

@@ -208,5 +208,25 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "4d6f",
+        "name": "Check that limit of 1 is rejected",
+        "category": [
+            "qdisc",
+            "sfq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+        ],
+        "cmdUnderTest": "./scripts/sfq_rejects_limit_1.py $DUMMY",
+        "expExitCode": "0",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "sfq",
+        "matchCount": "0",
+        "teardown": [
+        ]
     }
 ]