netdev - Re: [PATCH] libbpf: Fix is_pow_of

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Date:   Wed, 22 Jun 2022 08:20:10 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Zvi Effron <zeffron@...tgames.com>, Pavel Machek <pavel@....cz>
Cc:     Ian Rogers <irogers@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuze Chi <chiyuze@...gle.com>
Subject: Re: [PATCH] libbpf: Fix is_pow_of_2



On 06/22/2022 07:03 AM, Zvi Effron wrote:
> On Sun, Jun 19, 2022 at 12:13 PM Pavel Machek <pavel@....cz> wrote:
>>
>> Hi!
>>
>>> From: Yuze Chi <chiyuze@...gle.com>
>>>
>>> +++ b/tools/lib/bpf/libbpf.c
>>> @@ -4956,7 +4956,7 @@ static void bpf_map__destroy(struct bpf_map *map);
>>>
>>> static bool is_pow_of_2(size_t x)
>>> {
>>> - return x && (x & (x - 1));
>>> + return x && !(x & (x - 1));
>>> }
>>
>> I'm pretty sure we have this test in macro in includes somewhere... should we use
>> that instead?
>
> I went looking for a macro that provided this check and could not find one. I

arch/microblaze/mm/pgtable.c

#define is_power_of_2(x)	((x) != 0 && (((x) & ((x) - 1)) == 0))

> did find the inlined static function is_power_of_2 in log2.h, though, that we
> could use.

Here is a patch, but it seems that this is not worth the extra pain.

https://lore.kernel.org/bpf/8e5291b7-bd89-6fea-bfb7-954cacdb8523@iogearbox.net/

Thanks,
Tiezhu