netdev - Re: [PATCH bpf v2 2/2] selftests/bpf: Adjust data size to have ETH

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Message-ID: <35e5479b-420c-4fd9-80d9-c04530ef1dc2@linux.dev>
Date: Fri, 24 Jan 2025 11:22:16 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Shigeru Yoshida <syoshida@...hat.com>,
 Stanislav Fomichev <stfomichev@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
 hawk@...nel.org, lorenzo@...nel.org, toke@...hat.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH bpf v2 2/2] selftests/bpf: Adjust data size to have
 ETH_HLEN

On 1/23/25 6:45 PM, Stanislav Fomichev wrote:
> On 01/23, Martin KaFai Lau wrote:
>> 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@...hat.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.
> 
> Ah, yes, you're right, I missed the remaining parts that make sure
> the redirect happens

Thanks for confirming and the review.

Applied the fix.

Shigeru, please followup with a selftest to test the "less than ETH_HLEN" bug 
addressed in Patch 1. You can reuse some of the boilerplate codes from the 
xdp_cpumap_attach.c. The bpf prog can simply be "return XDP_PASS;" and ensure 
that BPF_F_TEST_XDP_LIVE_FRAMES is included in the bpf_test_run_opts. Thanks.