linux-kernel - Re: [PATCH bpf v2] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf

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Date:   Wed, 26 May 2021 09:34:19 -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>,
        KP Singh <kpsingh@...nel.org>,
        Brendan Jackman <jackmanb@...gle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf v2] libbpf: Move BPF_SEQ_PRINTF and BPF_SNPRINTF to bpf_helpers.h

On Tue, May 25, 2021 at 1:18 PM Florent Revest <revest@...omium.org> wrote:
>
> These macros are convenient wrappers around the bpf_seq_printf and
> bpf_snprintf helpers. They are currently provided by bpf_tracing.h which
> targets low level tracing primitives. bpf_helpers.h is a better fit.
>
> The __bpf_narg and __bpf_apply macros are needed in both files so
> provided twice and guarded by ifndefs.
>
> Reported-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Florent Revest <revest@...omium.org>
> ---
>  kernel/bpf/preload/iterators/iterators.bpf.c  |  1 -
>  tools/lib/bpf/bpf_helpers.h                   | 70 +++++++++++++++++++
>  tools/lib/bpf/bpf_tracing.h                   | 62 +++-------------
>  .../bpf/progs/bpf_iter_bpf_hash_map.c         |  1 -
>  .../selftests/bpf/progs/bpf_iter_bpf_map.c    |  1 -
>  .../selftests/bpf/progs/bpf_iter_ipv6_route.c |  1 -
>  .../selftests/bpf/progs/bpf_iter_netlink.c    |  1 -
>  .../selftests/bpf/progs/bpf_iter_task.c       |  1 -
>  .../selftests/bpf/progs/bpf_iter_task_btf.c   |  1 -
>  .../selftests/bpf/progs/bpf_iter_task_file.c  |  1 -
>  .../selftests/bpf/progs/bpf_iter_task_stack.c |  1 -
>  .../selftests/bpf/progs/bpf_iter_task_vma.c   |  1 -
>  .../selftests/bpf/progs/bpf_iter_tcp4.c       |  1 -
>  .../selftests/bpf/progs/bpf_iter_tcp6.c       |  1 -
>  .../selftests/bpf/progs/bpf_iter_udp4.c       |  1 -
>  .../selftests/bpf/progs/bpf_iter_udp6.c       |  1 -
>  .../selftests/bpf/progs/test_snprintf.c       |  1 -
>  17 files changed, 80 insertions(+), 67 deletions(-)
>
> diff --git a/kernel/bpf/preload/iterators/iterators.bpf.c b/kernel/bpf/preload/iterators/iterators.bpf.c
> index 52aa7b38e8b8..03af863314ea 100644
> --- a/kernel/bpf/preload/iterators/iterators.bpf.c
> +++ b/kernel/bpf/preload/iterators/iterators.bpf.c
> @@ -2,7 +2,6 @@
>  /* Copyright (c) 2020 Facebook */
>  #include <linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
> -#include <bpf/bpf_tracing.h>
>  #include <bpf/bpf_core_read.h>
>
>  #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
> diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> index 9720dc0b4605..68d992b30f26 100644
> --- a/tools/lib/bpf/bpf_helpers.h
> +++ b/tools/lib/bpf/bpf_helpers.h
> @@ -158,4 +158,74 @@ enum libbpf_tristate {
>  #define __kconfig __attribute__((section(".kconfig")))
>  #define __ksym __attribute__((section(".ksyms")))
>
> +#ifndef ___bpf_concat
> +#define ___bpf_concat(a, b) a ## b
> +#endif
> +#ifndef ___bpf_apply
> +#define ___bpf_apply(fn, n) ___bpf_concat(fn, n)
> +#endif
> +#ifndef ___bpf_nth
> +#define ___bpf_nth(_, _1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, N, ...) N
> +#endif
> +#ifndef ___bpf_narg
> +#define ___bpf_narg(...) \
> +       ___bpf_nth(_, ##__VA_ARGS__, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
> +#endif
> +#ifndef ___bpf_empty
> +#define ___bpf_empty(...) \
> +       ___bpf_nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
> +#endif

___bpf_empty doesn't seem to be used, let's remove it for now?
Otherwise it looks good.

> +
> +#define ___bpf_fill0(arr, p, x) do {} while (0)
> +#define ___bpf_fill1(arr, p, x) arr[p] = x
> +#define ___bpf_fill2(arr, p, x, args...) arr[p] = x; ___bpf_fill1(arr, p + 1, args)
> +#define ___bpf_fill3(arr, p, x, args...) arr[p] = x; ___bpf_fill2(arr, p + 1, args)
> +#define ___bpf_fill4(arr, p, x, args...) arr[p] = x; ___bpf_fill3(arr, p + 1, args)
> +#define ___bpf_fill5(arr, p, x, args...) arr[p] = x; ___bpf_fill4(arr, p + 1, args)
> +#define ___bpf_fill6(arr, p, x, args...) arr[p] = x; ___bpf_fill5(arr, p + 1, args)
> +#define ___bpf_fill7(arr, p, x, args...) arr[p] = x; ___bpf_fill6(arr, p + 1, args)
> +#define ___bpf_fill8(arr, p, x, args...) arr[p] = x; ___bpf_fill7(arr, p + 1, args)
> +#define ___bpf_fill9(arr, p, x, args...) arr[p] = x; ___bpf_fill8(arr, p + 1, args)
> +#define ___bpf_fill10(arr, p, x, args...) arr[p] = x; ___bpf_fill9(arr, p + 1, args)
> +#define ___bpf_fill11(arr, p, x, args...) arr[p] = x; ___bpf_fill10(arr, p + 1, args)
> +#define ___bpf_fill12(arr, p, x, args...) arr[p] = x; ___bpf_fill11(arr, p + 1, args)
> +#define ___bpf_fill(arr, args...) \
> +       ___bpf_apply(___bpf_fill, ___bpf_narg(args))(arr, 0, args)
> +

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