selftests: tc-testing: add tests for qfq mtu sanity check

QFQ only supports a certain bound of MTU size so make sure
we check for this requirement in the tests.
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Tested-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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

@@ -213,5 +213,53 @@
             "$TC qdisc del dev $DUMMY handle 1: root",
             "$IP link del dev $DUMMY type dummy"
         ]
+    },
+    {
+        "id": "85ee",
+        "name": "QFQ with big MTU",
+        "category": [
+            "qdisc",
+            "qfq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link add dev $DUMMY type dummy || /bin/true",
+            "$IP link set dev $DUMMY mtu 2147483647 || /bin/true",
+            "$TC qdisc add dev $DUMMY handle 1: root qfq"
+        ],
+        "cmdUnderTest": "$TC class add dev $DUMMY parent 1: classid 1:1 qfq weight 100",
+        "expExitCode": "2",
+        "verifyCmd": "$TC class show dev $DUMMY",
+        "matchPattern": "class qfq 1:",
+        "matchCount": "0",
+        "teardown": [
+            "$IP link del dev $DUMMY type dummy"
+        ]
+    },
+    {
+        "id": "ddfa",
+        "name": "QFQ with small MTU",
+        "category": [
+            "qdisc",
+            "qfq"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link add dev $DUMMY type dummy || /bin/true",
+            "$IP link set dev $DUMMY mtu 256 || /bin/true",
+            "$TC qdisc add dev $DUMMY handle 1: root qfq"
+        ],
+        "cmdUnderTest": "$TC class add dev $DUMMY parent 1: classid 1:1 qfq weight 100",
+        "expExitCode": "2",
+        "verifyCmd": "$TC class show dev $DUMMY",
+        "matchPattern": "class qfq 1:",
+        "matchCount": "0",
+        "teardown": [
+            "$IP link del dev $DUMMY type dummy"
+        ]
     }
 ]