selftests: tc-testing: add tx_queue_len cap regression tests

Add nine test cases for the S16_MAX tx_queue_len cap to the
pfifo_fast suite. Netlink cases exercise the ifla_policy bound
(2/3); the two new sysfs cases exercise the netif_change_tx_queue_len()
choke point that 1/3 owns (SIOCSIFTXQLEN shares it; the ioctl is not
portably reachable from tdc):

- dbe3: set txqueuelen 32767 (S16_MAX) - accepted, pins the exact
  boundary value.
- b50e: set txqueuelen 32768 - rejected with -ERANGE.
- 40f8: write 32768 to /sys/class/net/*/tx_queue_len - rejected
  (covers patch 1/3 directly; netlink cannot reach this path).
- 4b6e: write 32767 via sysfs - accepted, boundary positive control
  for the patch-1 path.
- b90d: create a dummy with txqueuelen 32767 - accepted.
- 57ab: create a dummy with txqueuelen 32768 - rejected at netlink
  parse time.
- e777: create a dummy with txqueuelen 500000 - rejected (the v1
  bypass path flagged by review).
- 31ac: create a veth with an oversized txqueuelen on the peer nest -
  rejected (the peer nest is parsed against ifla_policy too).
- b567: create a veth with txqueuelen on both ends within the cap -
  accepted (positive control for the peer nest).

The three negative-creation verifies assert device absence
("ip -o link show" must not contain the device), not merely absence
of a qlen pattern - the device does not exist when creation fails, so
the exit code carries the signal and the verify adds content.

The v1 04b5 "resize rollback" case is dropped: with the cap checked
first, netif_change_tx_queue_len() returns -ERANGE before the write,
the notifier or any qdisc resize, so the case exercised no resize and
no rollback. It was also nondeterministic: pre-patch, the resize
issues three ~11 MB kvmallocs for qlen 500000 which normally succeed,
so the case passed on an unfixed kernel only under memory pressure -
its outcome depended on the test host's free memory.

Test commands run inside the netns, but nsPlugin creates the veth
peer in the root namespace, so the teardown deletes the in-ns end
only; deleting the peer via the pair is implicit.

Note: iproute2 treats "txqueuelen" appearing after "type X" as a
link-type attribute and silently drops it, so the creation cases
place it before "type" to actually reach the kernel.

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/QDISC-2899.v2.20260901233641@mojatatu.com.3
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions