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Subject: Re: [PATCH] selftests/bpf: Fix return value check in attach_bpf()
To:     Daniel Borkmann <daniel@iogearbox.net>, <shuah@kernel.org>,
        <ast@kernel.org>, <andrii@kernel.org>
CC:     <linux-kselftest@vger.kernel.org>, <netdev@vger.kernel.org>,
        <bpf@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <yi.zhang@huawei.com>
References: <20210528090758.1108464-1-yukuai3@huawei.com>
 <c5a37d91-dd20-55e3-a78b-272a00b940d5@iogearbox.net>
From:   "yukuai (C)" <yukuai3@huawei.com>
Message-ID: <b22eac4a-aad5-917d-5f26-7955b798779b@huawei.com>
Date:   Sat, 29 May 2021 09:25:28 +0800
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On 2021/05/29 4:46, Daniel Borkmann wrote:
> On 5/28/21 11:07 AM, Yu Kuai wrote:
>> use libbpf_get_error() to check the return value of
>> bpf_program__attach().
>>
>> Reported-by: Hulk Robot <hulkci@huawei.com>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   tools/testing/selftests/bpf/benchs/bench_rename.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/benchs/bench_rename.c 
>> b/tools/testing/selftests/bpf/benchs/bench_rename.c
>> index c7ec114eca56..b7d4a1d74fca 100644
>> --- a/tools/testing/selftests/bpf/benchs/bench_rename.c
>> +++ b/tools/testing/selftests/bpf/benchs/bench_rename.c
>> @@ -65,7 +65,7 @@ static void attach_bpf(struct bpf_program *prog)
>>       struct bpf_link *link;
>>       link = bpf_program__attach(prog);
>> -    if (!link) {
>> +    if (libbpf_get_error(link)) {
>>           fprintf(stderr, "failed to attach program!\n");
>>           exit(1);
>>       }
> 
> Could you explain the rationale of this patch? bad2e478af3b 
> ("selftests/bpf: Turn
> on libbpf 1.0 mode and fix all IS_ERR checks") explains: 'Fix all the 
> explicit
> IS_ERR checks that now will be broken because libbpf returns NULL on 
> error (and
> sets errno).' So the !link check looks totally reasonable to me. 
> Converting to
> libbpf_get_error() is not wrong in itself, but given you don't make any 
> use of
> the err code, there is also no point in this diff here.
Hi,

I was thinking that bpf_program__attach() can return error code
theoretically(for example -ESRCH), and such case need to be handled.

Thanks,
Yu Kuai
> 
> Thanks,
> Daniel
> .
>