Subject: Re: [PATCH bpf 2/2] selftests/bpf: Update xdp_context_test_run test to check maximum metadata size

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Mon, 05 Jan 2026 20:04:24 +0100

Amery Hung <[email-masked]> writes:

> On Mon, Jan 5, 2026 at 3:48 AM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> Update the selftest to check that the metadata size check takes the
>> xdp_frame size into account in bpf_prog_test_run. The original
>> check (for meta size 256) was broken because the data frame supplied was
>> smaller than this, triggering a different EINVAL return. So supply a
>> larger data frame for this test to make sure we actually exercise the
>> check we think we are.
>>
>> Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
>> ---
>>  .../bpf/prog_tests/xdp_context_test_run.c          | 14 +++++++++++---
>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
>> index ee94c281888a..24d7d6d8fea1 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
>> @@ -47,6 +47,7 @@ void test_xdp_context_test_run(void)
>>         struct test_xdp_context_test_run *skel = NULL;
>>         char data[sizeof(pkt_v4) + sizeof(__u32)];
>>         char bad_ctx[sizeof(struct xdp_md) + 1];
>> +       char large_data[256];
>>         struct xdp_md ctx_in, ctx_out;
>>         DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
>>                             .data_in = &data,
>> @@ -94,9 +95,6 @@ void test_xdp_context_test_run(void)
>>         test_xdp_context_error(prog_fd, opts, 4, sizeof(__u32), sizeof(data),
>>                                0, 0, 0);
>>
>> -       /* Meta data must be 255 bytes or smaller */
>> -       test_xdp_context_error(prog_fd, opts, 0, 256, sizeof(data), 0, 0, 0);
>> -
>>         /* Total size of data must be data_end - data_meta or larger */
>>         test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32),
>>                                sizeof(data) + 1, 0, 0, 0);
>> @@ -116,6 +114,16 @@ void test_xdp_context_test_run(void)
>>         test_xdp_context_error(prog_fd, opts, 0, sizeof(__u32), sizeof(data),
>>                                0, 0, 1);
>>
>> +       /* Meta data must be 216 bytes or smaller (256 - sizeof(struct
>> +        * xdp_frame)). Test both nearest invalid size and nearest invalid
>> +        * 4-byte-aligned size, and make sure data_in is large enough that we
>> +        * actually hit the cheeck on metadata length
>
> nit: a typo here: cheeck -> check

Oops. Will leave this for the maintainers to fix up unless there's
another reason to respin, though...

>> +        */
>> +       opts.data_in = large_data;
>> +       opts.data_size_in = sizeof(large_data);
>> +       test_xdp_context_error(prog_fd, opts, 0, 217, sizeof(large_data), 0, 0, 0);
>> +       test_xdp_context_error(prog_fd, opts, 0, 220, sizeof(large_data), 0, 0, 0);
>> +
>>         test_xdp_context_test_run__destroy(skel);
>>  }
>
> Reviewed-by: Amery Hung <[email-masked]>

Thanks!

-Toke