linux-kernel - Re: [PATCH bpf-next v2 5/6] libbpf: Introduce a BPF

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Date:   Fri, 26 Mar 2021 16:02:32 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Florent Revest <revest@...omium.org>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 5/6] libbpf: Introduce a BPF_SNPRINTF helper macro

On Tue, Mar 23, 2021 at 7:23 PM Florent Revest <revest@...omium.org> wrote:
>
> Similarly to BPF_SEQ_PRINTF, this macro turns variadic arguments into an
> array of u64, making it more natural to call the bpf_snprintf helper.
>
> Signed-off-by: Florent Revest <revest@...omium.org>
> ---
>  tools/lib/bpf/bpf_tracing.h | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
> index d9a4c3f77ff4..e5c6ede6060b 100644
> --- a/tools/lib/bpf/bpf_tracing.h
> +++ b/tools/lib/bpf/bpf_tracing.h
> @@ -447,4 +447,22 @@ static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
>                 __ret;                                                      \
>         })
>
> +/*
> + * BPF_SNPRINTF wraps the bpf_snprintf helper with variadic arguments instead of
> + * an array of u64.
> + */
> +#define BPF_SNPRINTF(out, out_size, fmt, args...)                          \
> +       ({                                                                  \

Same feedback as the previous patch, but let's also reduce the
nestedness level, those ({ }) can be shifted one tab left, right?
Please do the same for the previous patch as well. Thanks!

> +               _Pragma("GCC diagnostic push")                              \
> +               _Pragma("GCC diagnostic ignored \"-Wint-conversion\"")      \
> +               unsigned long long ___param[___bpf_narg(args)];             \
> +               static const char ___fmt[] = fmt;                           \
> +               int __ret;                                                  \
> +               ___bpf_fill(___param, args);                                \
> +               _Pragma("GCC diagnostic pop")                               \
> +               __ret = bpf_snprintf(out, out_size, ___fmt,                 \
> +                                    ___param, sizeof(___param));           \
> +               __ret;                                                      \
> +       })
> +
>  #endif
> --
> 2.31.0.291.g576ba9dcdaf-goog
>