Add two test cases for the pfifo_fast ring size cap:

1. Init path: set txqueuelen to 100000000, attempt to attach pfifo_fast.
   On a fixed kernel the qdisc add is rejected with -ERANGE (exit code 2).
   On an unfixed kernel the allocation either succeeds or triggers OOM.

2. Resize path: attach pfifo_fast with default txqueuelen, then raise
   txqueuelen to 100000000. On a fixed kernel the resize is rejected
   with -ERANGE and txqueuelen rolls back to the original value (1000).
   On an unfixed kernel the ring is resized to the oversized value.

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 .../tc-tests/qdiscs/pfifo_fast.json           | 60 +++++++++++++++++--
 1 file changed, 54 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json
index 30da27fe8806..46b54ae37a91 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/pfifo_fast.json
@@ -9,8 +9,7 @@
         "plugins": {
             "requires": "nsPlugin"
         },
-        "setup": [
-        ],
+        "setup": [],
         "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root pfifo_fast",
         "expExitCode": "0",
         "verifyCmd": "$TC qdisc show dev $DUMMY",
@@ -30,8 +29,7 @@
         "plugins": {
             "requires": "nsPlugin"
         },
-        "setup": [
-        ],
+        "setup": [],
         "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root pfifo_fast",
         "expExitCode": "0",
         "verifyCmd": "$TC -s qdisc show dev $DUMMY",
@@ -81,8 +79,7 @@
         "verifyCmd": "$TC qdisc show dev $DUMMY",
         "matchPattern": "qdisc pfifo_fast 1: root refcnt [0-9]+ bands 3 priomap",
         "matchCount": "0",
-        "teardown": [
-        ]
+        "teardown": []
     },
     {
         "id": "4385",
@@ -105,5 +102,56 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "7d12",
+        "name": "Reject pfifo_fast init with tx_queue_len exceeding S16_MAX",
+        "category": [
+            "qdisc",
+            "pfifo_fast"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$IP link set dev $DUMMY txqueuelen 100000000"
+        ],
+        "cmdUnderTest": "$TC qdisc add dev $DUMMY handle 1: root pfifo_fast",
+        "expExitCode": "2",
+        "verifyCmd": "$TC qdisc show dev $DUMMY",
+        "matchPattern": "qdisc pfifo_fast 1: root",
+        "matchCount": "0",
+        "teardown": [
+            "$IP link set dev $DUMMY txqueuelen 1000",
+            [
+                "$TC qdisc del dev $DUMMY handle 1: root",
+                0,
+                1,
+                2,
+                255
+            ]
+        ]
+    },
+    {
+        "id": "d09b",
+        "name": "Reject pfifo_fast resize when tx_queue_len exceeds S16_MAX",
+        "category": [
+            "qdisc",
+            "pfifo_fast"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY handle 1: root pfifo_fast"
+        ],
+        "cmdUnderTest": "$IP link set dev $DUMMY txqueuelen 100000000",
+        "expExitCode": "2",
+        "verifyCmd": "$IP link show dev $DUMMY",
+        "matchPattern": "qlen 1000$",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY handle 1: root"
+        ]
     }
 ]
-- 
2.43.0