Add a tdc test case (7ec8) that fills the u32 node ID space with 4095
auto-generated handles, then attempts to add a 4096th. On the fixed
kernel the 4096th filter is rejected with ENOSPC (exit 2). On the
unfixed kernel it silently succeeds with a duplicate handle.

Fixes: e7614370d6f04 ("net_sched: use idr to allocate u32 filter handles")
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 .../tc-testing/tc-tests/filters/u32.json      | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json b/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
index b2ca9d4e991b..b9019b14d05c 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/filters/u32.json
@@ -353,5 +353,28 @@
         "teardown": [
             "$TC qdisc del dev $DEV1 parent root drr"
         ]
+    },
+    {
+        "id": "7ec8",
+        "name": "Add u32 filter when node ID pool is exhausted (4096th filter rejected)",
+        "category": [
+            "filter",
+            "u32"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DUMMY clsact",
+            "yes 'filter add dev $DUMMY ingress prio 1 protocol ip u32 match u8 0 0 at 0' | head -n 4095 | $TC -b -"
+        ],
+        "cmdUnderTest": "$TC filter add dev $DUMMY ingress prio 1 protocol ip u32 match u8 0 0 at 0",
+        "expExitCode": "2",
+        "verifyCmd": "$TC filter show dev $DUMMY ingress",
+        "matchPattern": "pref 1 u32",
+        "matchCount": "4095",
+        "teardown": [
+            "$TC qdisc del dev $DUMMY clsact"
+        ]
     }
 ]
-- 
2.43.0