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)