[PATCH net-next v2 0/4] selftest: net: Add selftest for netpoll

[Breno Leitao <leitao@debian.org>]

I am submitting a new selftest for the netpoll subsystem specifically
targeting the case where the RX is polling in the TX path, which is
a case that we don't have any test in the tree today. This is done when
netpoll_poll_dev() called, and this test creates a scenario when that is
probably.

The test does the following:

1) Configuring a single RX/TX queue to increase contention on the
   interface.
2) Generating background traffic to saturate the network, mimicking
   real-world congestion.
3) Sending netconsole messages to trigger netpoll polling and monitor
   its behavior.
4) Using dynamic netconsole targets via configfs, with the ability to
   delete and recreate targets during the test.
5) Running bpftrace in parallel to verify that netpoll_poll_dev() is
   called when expected. If it is called, then the test passes,
   otherwise the test is marked as skipped.

In order to achieve it, I stole Jakub's bpftrace helper from [1], and
did some small changes that I found useful to use the helper.

So, this patchset basically contains:

1) The code stolen from Jakub
2) Improvements on bpftrace() helper
3) The selftest itself

Link: https://lore.kernel.org/all/20250421222827.283737-22-kuba@kernel.org/ [1]

---
Changes in v1 (from RFC):
- Toggle the netconsole interfaces up and down after 5 iterations.
- Moved the traffic check under DEBUG (Willem de Bruijn).
- Bumped the iterations to 20 given it runs faster now.
- Link to the RFC: https://lore.kernel.org/r/20250612-netpoll_test-v1-1-4774fd95933f@debian.org

---
Changes in v2:
- Stole Jakub's helper to run bpftrace
- Removed the DEBUG option and moved logs to logging
- Change the code to have a higher chance of calling netpoll_poll_dev().
  In my current configuration, it is hitting multiple times during the
  test.
- Save and restore TX/RX queue size (Jakub)
- Link to v1: https://lore.kernel.org/r/20250620-netpoll_test-v1-1-5068832f72fc@debian.org

---
Breno Leitao (3):
      selftests: drv-net: Improve bpftrace utility error handling
      selftests: drv-net: Strip '@' prefix from bpftrace map keys
      selftests: net: add netpoll basic functionality test

Jakub Kicinski (1):
      selftests: drv-net: add helper/wrapper for bpftrace

 tools/testing/selftests/drivers/net/Makefile       |   1 +
 .../testing/selftests/drivers/net/netpoll_basic.py | 344 +++++++++++++++++++++
 tools/testing/selftests/net/lib/py/utils.py        |  38 +++
 3 files changed, 383 insertions(+)
---
base-commit: eb4c27edb4d8dbfbdcc7bc03e0394a0fab8af7d5
change-id: 20250612-netpoll_test-a1324d2057c8

Best regards,
--  
Breno Leitao <leitao@debian.org>