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 <victor@mojatatu.com>
Tested-by: hybris <hybris@mojatatu.ai>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/QDISC-CTUU.v3.20260916184908@mojatatu.com.2
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions