linux-kernel - Re: [PATCH bpf-next v1] bpftool: Add support for custom BTF path in prog load/loadall

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Message-ID: <CAADnVQJJ7pLsm0UTzPOj1H+rdaaY7Lv0As0Te-b+7zieQbntkw@mail.gmail.com>
Date: Tue, 13 May 2025 14:19:13 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: bpf <bpf@...r.kernel.org>, Quentin Monnet <qmo@...nel.org>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1] bpftool: Add support for custom BTF path in
 prog load/loadall

On Mon, May 12, 2025 at 8:59 PM Jiayuan Chen <jiayuan.chen@...ux.dev> wrote:
>
> This patch exposes the btf_custom_path feature to bpftool, allowing users
> to specify a custom BTF file when loading BPF programs using prog load or
> prog loadall commands. This feature is already supported by libbpf, and
> this patch makes it accessible through the bpftool command-line interface.
>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@...ux.dev>
> ---
>  tools/bpf/bpftool/prog.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index f010295350be..63f84e765b34 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -1681,8 +1681,17 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
>                 } else if (is_prefix(*argv, "autoattach")) {
>                         auto_attach = true;
>                         NEXT_ARG();
> +               } else if (is_prefix(*argv, "custom_btf")) {
> +                       NEXT_ARG();
> +
> +                       if (!REQ_ARGS(1))
> +                               goto err_free_reuse_maps;
> +
> +                       open_opts.btf_custom_path = GET_ARG();

I don't see a use case yet.
What exactly is the scenario where it's useful ?