netdev - Re: [PATCH bpf-next v2] libbpf: Include linux/log2.h to use is_power_of

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Date:   Mon, 20 Jun 2022 14:39:34 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v2] libbpf: Include linux/log2.h to use
 is_power_of_2()

On 6/20/22 10:23 AM, Tiezhu Yang wrote:
> is_power_of_2() is already defined in tools/include/linux/log2.h [1],
> so no need to define it again in tools/lib/bpf/libbpf_internal.h, so
> just include linux/log2.h directly.
> 
> [1] https://lore.kernel.org/bpf/20220619171248.GC3362@bug/
> 
> Suggested-by: Pavel Machek <pavel@....cz>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   tools/lib/bpf/libbpf.c          | 2 +-
>   tools/lib/bpf/libbpf_internal.h | 6 +-----
>   tools/lib/bpf/linker.c          | 2 +-
>   3 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 49e359c..5252e51 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -5131,7 +5131,7 @@ static size_t adjust_ringbuf_sz(size_t sz)
>   	 * a power-of-2 multiple of kernel's page size. If user diligently
>   	 * satisified these conditions, pass the size through.
>   	 */
> -	if ((sz % page_sz) == 0 && is_pow_of_2(sz / page_sz))
> +	if ((sz % page_sz) == 0 && is_power_of_2(sz / page_sz))
>   		return sz;
>   
>   	/* Otherwise find closest (page_sz * power_of_2) product bigger than
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index a1ad145..021946a 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -13,6 +13,7 @@
>   #include <limits.h>
>   #include <errno.h>
>   #include <linux/err.h>
> +#include <linux/log2.h>
>   #include <fcntl.h>
>   #include <unistd.h>
>   #include "libbpf_legacy.h"
> @@ -582,9 +583,4 @@ struct bpf_link * usdt_manager_attach_usdt(struct usdt_manager *man,
>   					   const char *usdt_provider, const char *usdt_name,
>   					   __u64 usdt_cookie);
>   
> -static inline bool is_pow_of_2(size_t x)
> -{
> -	return x && (x & (x - 1)) == 0;
> -}

I don't think this is worth the extra pain and I would just leave above as-is, because then
we would also need a `LGPL-2.1 OR BSD-2-Clause` compatible reimplementation of linux/log2.h
header inside the standalone repo https://github.com/libbpf/libbpf/tree/master/include/linux
in order to build libbpf there once this get imported to it.

>   #endif /* __LIBBPF_LIBBPF_INTERNAL_H */
> diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
> index 4ac02c2..b2edb5f 100644
> --- a/tools/lib/bpf/linker.c
> +++ b/tools/lib/bpf/linker.c
> @@ -719,7 +719,7 @@ static int linker_sanity_check_elf(struct src_obj *obj)
>   			return -EINVAL;
>   		}
>   
> -		if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
> +		if (sec->shdr->sh_addralign && !is_power_of_2(sec->shdr->sh_addralign))
>   			return -EINVAL;
>   		if (sec->shdr->sh_addralign != sec->data->d_align)
>   			return -EINVAL;
>