[PATCH net-next v4 0/3] 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 v4:
- Make the test XFail if it doesn't hit the function we are looking for
- Toggle the interface while the traffic is flowing.
- Bumped the number of messages from 10 to 40 per iterations.
   * This is hitting ~15 times per run on my vng test.
- Decreased the time from 15 seconds to 10 seconds, given that if
  it didn't hit the function in 10 seconds, 5 seconds extra will not
  help.
- Link to v3: https://lore.kernel.org/r/20250627-netpoll_test-v3-0-575bd200c8a9@debian.org

Changes in v3:
- Make pylint happy (Simon)
- Remove the unnecessary patch in bpftrace to raise an exception when it
  fails. (Jakub)
- Improved the bpftrace code (Willem)
- Stop sending messages if bpftrace is not alive anymore.
- Link to v2: https://lore.kernel.org/r/20250625-netpoll_test-v2-0-47d27775222c@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 (2):
      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 +
 .../selftests/drivers/net/lib/py/__init__.py       |   3 +-
 .../testing/selftests/drivers/net/netpoll_basic.py | 365 +++++++++++++++++++++
 tools/testing/selftests/net/lib/py/utils.py        |  35 ++
 4 files changed, 403 insertions(+), 1 deletion(-)
---
base-commit: 22e1cfda0f612556f116560d2b7e9c3315636bfb
change-id: 20250612-netpoll_test-a1324d2057c8

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