Re: [PATCH bpf v2 2/2] selftests/bpf: Adjust data size to have ETH_HLEN

[Martin KaFai Lau <martin.lau@linux.dev>]

On 1/23/25 11:18 AM, Stanislav Fomichev wrote:
> On 01/22, Shigeru Yoshida wrote:
>> The function bpf_test_init() now returns an error if user_size
>> (.data_size_in) is less than ETH_HLEN, causing the tests to
>> fail. Adjust the data size to ensure it meets the requirement of
>> ETH_HLEN.
>>
>> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
>> ---
>>   .../testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c  | 4 ++--
>>   .../testing/selftests/bpf/prog_tests/xdp_devmap_attach.c  | 8 ++++----
>>   2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c b/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c
>> index c7f74f068e78..df27535995af 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_cpumap_attach.c
>> @@ -52,10 +52,10 @@ static void test_xdp_with_cpumap_helpers(void)
>>   	ASSERT_EQ(info.id, val.bpf_prog.id, "Match program id to cpumap entry prog_id");
>>   
>>   	/* send a packet to trigger any potential bugs in there */
>> -	char data[10] = {};
>> +	char data[ETH_HLEN] = {};
>>   	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
>>   			    .data_in = &data,
>> -			    .data_size_in = 10,
>> +			    .data_size_in = sizeof(data),
>>   			    .flags = BPF_F_TEST_XDP_LIVE_FRAMES,
>>   			    .repeat = 1,
>>   		);
> 
> We should still keep 10, but change the ASSERT_OK below to expect the
> error instead. Looking at the comment above, the purpose of the test
> is to exercise that error case.
> 

I think the bpf_prog_test_run_opts in this dev/cpumap test is to check the 
bpf_redirect_map() helper, so it expects the bpf_prog_test_run_opts to succeed.

It just happens the current data[10] cannot trigger the fixed bug because the 
bpf prog returns a XDP_REDIRECT instead of XDP_PASS, so xdp_recv_frames is not 
called.

To test patch 1, a separate test is probably needed to trigger the bug in 
xdp_recv_frames() with a bpf prog returning XDP_PASS.