Re: [PATCH net-next v6 3/3] selftests: drv-net: Test queue xsk attribute

[Joe Damato <jdamato@fastly.com>]

On Tue, Feb 11, 2025 at 12:09:50PM +0100, Paolo Abeni wrote:
> On 2/10/25 8:38 PM, Joe Damato wrote:
> > +def check_xdp(cfg, nl, xdp_queue_id=0) -> None:
> > +    test_dir = os.path.dirname(os.path.realpath(__file__))
> > +    xdp = subprocess.Popen([f"{test_dir}/xdp_helper", f"{cfg.ifindex}", f"{xdp_queue_id}"],
> > +                           stdin=subprocess.PIPE, stdout=subprocess.PIPE, bufsize=1,
> > +                           text=True)
> > +    defer(xdp.kill)
> > +
> > +    stdout, stderr = xdp.communicate(timeout=10)
> > +    rx = tx = False
> > +
> > +    queues = nl.queue_get({'ifindex': cfg.ifindex}, dump=True)
> > +    if not queues:
> > +        raise KsftSkipEx("Netlink reports no queues")
> > +
> > +    for q in queues:
> > +        if q['id'] == 0:
> > +            if q['type'] == 'rx':
> > +                rx = True
> > +            if q['type'] == 'tx':
> > +                tx = True
> > +
> > +            ksft_eq(q['xsk'], {})
> > +        else:
> > +            if 'xsk' in q:
> > +                _fail("Check failed: xsk attribute set.")
> > +
> > +    ksft_eq(rx, True)
> > +    ksft_eq(tx, True)
> 
> This causes self-test failures:
> 
> https://netdev-3.bots.linux.dev/vmksft-net-drv/results/987742/4-queues-py/stdout
> 
> but I really haven't done any real investigation here.

I think it's because the test kernel in this case has
CONFIG_XDP_SOCKETS undefined [1].

The error printed in the link you mentioned:

  socket creation failed: Address family not supported by protocol

is coming from the C program, which fails to create the AF_XDP
socket.

I think the immediate reaction is to add more error checking to the
python to make sure that the subprocess succeeded and if it failed,
skip.

But, we may want it to fail for other error states instead of
skipping? Not sure if there's general guidance on this, but my plan
was to have the AF_XDP socket creation failure return a different
error code (I dunno maybe -1?) and only skip the test in that case.

Will that work or is there a better way? I only want to skip if
AF_XDP doesn't exist in the test kernel.

[1]: https://netdev-3.bots.linux.dev/vmksft-net-drv/results/987742/config