Re: [PATCH] selftests/bpf: Fix return value check in attach_bpf()

From: Daniel Borkmann <daniel@iogearbox.net>
To: Yu Kuai <yukuai3@huawei.com>,
	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
Subject: Re: [PATCH] selftests/bpf: Fix return value check in attach_bpf()
Date: Fri, 28 May 2021 22:46:23 +0200	[thread overview]
Message-ID: <c5a37d91-dd20-55e3-a78b-272a00b940d5@iogearbox.net> (raw)
In-Reply-To: <20210528090758.1108464-1-yukuai3@huawei.com>

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.

Thanks,
Daniel