[PATCH net v3 2/2] selftests: tc-testing: add a lateral-drift hfsc classify-walk test

The classify-loop fix bounds a walk's non-descending hops, so the guard
must not misfire on a legal walk that reaches its leaf through a
level-drift lateral chain. Add a case that builds exactly that chain and
asserts traffic still reaches the chain's own leaf.

A lateral hop can only exist because a bind was legal when it was made
and a later class add raised the target's level, so the setup binds each
hop while the target is still a leaf and only then deepens it: bind
1:1 -> 1:2 while 1:2 is a leaf, add 1:20 under 1:2, add 1:3 and bind
1:2 -> 1:3 while 1:3 is a leaf, then add 1:30 and 1:31 under 1:3 and
bind 1:3 -> 1:31. The walk root -> 1:1 -> 1:2 -> 1:3 -> 1:31 then takes
two lateral hops and must reach leaf 1:31.

The default class is 1:30, distinct from the asserted leaf, and the
verify pattern is anchored to the 1:31 stats line, so neither a
fall-through to the default nor a nonzero count on another class can
satisfy the check. On the patched kernel the test passes; with the bound
forced to zero the walk falls to the default and 1:31 stays idle, so the
test fails.

Reviewed-by: Victor Nogueira <redacted>
Tested-by: hybris <redacted>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
v3:
   -  Build the lateral chain by binding each hop while its target is
      still a leaf and deepening afterwards, instead of deepening first
      (Sashiko: nipa, gemini)
   -  Make the default class 1:30 distinct from the asserted leaf 1:31
      and anchor the verify pattern to the 1:31 stats line. (Sashiko:
      nipa)
   -  Drop the trailing "sleep 1" so ping's exit status is the one
      checked and no command escapes the test netns. (Sashiko: nipa)
v2:
   -  First version of the lateral-drift regression test.
---
 .../tc-testing/tc-tests/qdiscs/hfsc.json      | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json
index c98c339424d4..4f6bbb8b57f9 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json

@@ -169,5 +169,39 @@
         "teardown": [
             "$TC qdisc del dev $DUMMY handle 1: root"
         ]
+    },
+    {
+        "id": "8c39",
+        "name": "HFSC classify walk still reaches leaf after lateral drift",
+        "category": [
+            "qdisc",
+            "hfsc"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "ip link set lo up",
+            "$TC qdisc add dev lo handle 1: root hfsc default 30",
+            "$TC class add dev lo parent 1: classid 1:1 hfsc rt m2 100kbit",
+            "$TC class add dev lo parent 1:1 classid 1:10 hfsc rt m2 50kbit",
+            "$TC class add dev lo parent 1: classid 1:2 hfsc rt m2 100kbit",
+            "$TC filter add dev lo parent 1: protocol ip prio 1 u32 match u8 0 0 at 0 flowid 1:1",
+            "$TC filter add dev lo parent 1:1 protocol ip prio 1 u32 match u8 0 0 at 0 flowid 1:2",
+            "$TC class add dev lo parent 1:2 classid 1:20 hfsc rt m2 10kbit",
+            "$TC class add dev lo parent 1: classid 1:3 hfsc rt m2 100kbit",
+            "$TC filter add dev lo parent 1:2 protocol ip prio 1 u32 match u8 0 0 at 0 flowid 1:3",
+            "$TC class add dev lo parent 1:3 classid 1:30 hfsc rt m2 10kbit",
+            "$TC class add dev lo parent 1:3 classid 1:31 hfsc rt m2 100kbit",
+            "$TC filter add dev lo parent 1:3 protocol ip prio 1 u32 match u8 0 0 at 0 flowid 1:31"
+        ],
+        "cmdUnderTest": "ping -n -c 10 -W 1 127.0.0.1",
+        "expExitCode": "0",
+        "verifyCmd": "$TC -s class show dev lo",
+        "matchPattern": "class hfsc 1:31 parent 1:3 rt[^\\n]*\\n Sent [0-9]+ bytes [1-9][0-9]* pkt",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev lo handle 1: root"
+        ]
     }
 ]

-- 
2.43.0