linux-kernel - Re: [RESEND][PATCH 4/6] libbpf: Introduce bpf_btf_get_fd_by_id

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Date:   Wed, 5 Oct 2022 16:06:43 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, mykolal@...com,
        shuah@...nel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [RESEND][PATCH 4/6] libbpf: Introduce bpf_btf_get_fd_by_id_opts()

On Tue, Oct 4, 2022 at 6:18 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Introduce bpf_btf_get_fd_by_id_opts(), for symmetry with
> bpf_map_get_fd_by_id_opts(), to let the caller pass the newly introduced
> data structure bpf_get_fd_opts. Keep the existing bpf_btf_get_fd_by_id(),
> and call bpf_btf_get_fd_by_id_opts() with NULL as opts argument, to prevent
> setting open_flags.
>
> Currently, the kernel does not support non-zero open_flags for
> bpf_btf_get_fd_by_id_opts(), and a call with them will result in an error
> returned by the bpf() system call. The caller should always pass zero
> open_flags.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  tools/lib/bpf/bpf.c      | 12 +++++++++++-
>  tools/lib/bpf/bpf.h      |  2 ++
>  tools/lib/bpf/libbpf.map |  1 +
>  3 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 92464c2d1da7..f43e8c8afbd3 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -980,19 +980,29 @@ int bpf_map_get_fd_by_id(__u32 id)
>         return bpf_map_get_fd_by_id_opts(id, NULL);
>  }
>
> -int bpf_btf_get_fd_by_id(__u32 id)
> +int bpf_btf_get_fd_by_id_opts(__u32 id,
> +                             const struct bpf_get_fd_opts *opts)
>  {
>         const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
>         union bpf_attr attr;
>         int fd;
>
> +       if (!OPTS_VALID(opts, bpf_get_fd_opts))
> +               return libbpf_err(-EINVAL);
> +
>         memset(&attr, 0, attr_sz);
>         attr.btf_id = id;
> +       attr.open_flags = OPTS_GET(opts, open_flags, 0);
>
>         fd = sys_bpf_fd(BPF_BTF_GET_FD_BY_ID, &attr, attr_sz);
>         return libbpf_err_errno(fd);
>  }
>
> +int bpf_btf_get_fd_by_id(__u32 id)
> +{
> +       return bpf_btf_get_fd_by_id_opts(id, NULL);
> +}
> +
>  int bpf_link_get_fd_by_id(__u32 id)
>  {
>         const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 595d342fb7f9..559af0b84299 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -379,6 +379,8 @@ LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
>  LIBBPF_API int bpf_map_get_fd_by_id_opts(__u32 id,
>                                          const struct bpf_get_fd_opts *opts);
>  LIBBPF_API int bpf_map_get_fd_by_id(__u32 id);
> +LIBBPF_API int bpf_btf_get_fd_by_id_opts(__u32 id,
> +                                        const struct bpf_get_fd_opts *opts);

It's subjective, but opts variants of APIs, being more "advanced"
usually are listed after their simpler non-opts variants. Can you
please add new _opts APIs after their non-opts variants?

>  LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
>  LIBBPF_API int bpf_link_get_fd_by_id(__u32 id);
>  LIBBPF_API int bpf_obj_get_info_by_fd(int bpf_fd, void *info, __u32 *info_len);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index c3604eaa220d..7011d5eec67b 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -371,6 +371,7 @@ LIBBPF_1.0.0 {
>
>  LIBBPF_1.1.0 {
>         global:
> +               bpf_btf_get_fd_by_id_opts;
>                 bpf_map_get_fd_by_id_opts;
>                 bpf_prog_get_fd_by_id_opts;
>                 user_ring_buffer__discard;
> --
> 2.25.1
>