linux-kernel - Re: [RFC PATCH v1 1/1] bpftool: Add generating command to C dumped file.

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Message-Id: <Ys3d7LCN8yATY9az@google.com>
Date:   Tue, 12 Jul 2022 13:47:40 -0700
From:   sdf@...gle.com
To:     Francis Laniel <flaniel@...ux.microsoft.com>
Cc:     bpf@...r.kernel.org, Quentin Monnet <quentin@...valent.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 1/1] bpftool: Add generating command to C dumped file.

On 07/12, Francis Laniel wrote:
> This commit adds the following lines to file generated by dump:
> /*
>   * File generated by bpftool using:
>   * bpftool btf dump file /sys/kernel/btf/vmlinux format c
>   * DO NOT EDIT.
>   */
> This warns users to not edit the file and documents the command used to
> generate the file.

> Signed-off-by: Francis Laniel <flaniel@...ux.microsoft.com>
> ---
>   tools/bpf/bpftool/btf.c | 16 ++++++++++++++--
>   1 file changed, 14 insertions(+), 2 deletions(-)

> diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
> index 7e6accb9d9f7..eecfc27370c3 100644
> --- a/tools/bpf/bpftool/btf.c
> +++ b/tools/bpf/bpftool/btf.c
> @@ -415,7 +415,8 @@ static void __printf(2, 0) btf_dump_printf(void *ctx,
>   }

>   static int dump_btf_c(const struct btf *btf,
> -		      __u32 *root_type_ids, int root_type_cnt)
> +		      __u32 *root_type_ids, int root_type_cnt,
> +		      int argc, char **argv)
>   {
>   	struct btf_dump *d;
>   	int err = 0, i;
> @@ -425,6 +426,14 @@ static int dump_btf_c(const struct btf *btf,
>   	if (err)
>   		return err;

> +	printf("/*\n");
> +	printf(" * File generated by bpftool using:\n");
> +	printf(" * bpftool btf dump");

[..]

> +	for (i = 0; i < argc; i++)
> +		printf(" %s", argv[i]);

Do we really need that complexity to preserve the arguments?
For skeletons we're simply doing:

	/* THIS FILE IS AUTOGENERATED BY BPFTOOL! */

So probably the same should be fine here?

Also, while at it, might be worth adding SPDX license comment? So let's
align with whatever we have in gen.c ?


> +	printf("\n");
> +	printf(" * DO NOT EDIT.\n");
> +	printf(" */\n");
>   	printf("#ifndef __VMLINUX_H__\n");
>   	printf("#define __VMLINUX_H__\n");
>   	printf("\n");
> @@ -507,8 +516,10 @@ static bool btf_is_kernel_module(__u32 btf_id)
>   static int do_dump(int argc, char **argv)
>   {
>   	struct btf *btf = NULL, *base = NULL;
> +	char **orig_argv = argv;
>   	__u32 root_type_ids[2];
>   	int root_type_cnt = 0;
> +	int orig_argc = argc;
>   	bool dump_c = false;
>   	__u32 btf_id = -1;
>   	const char *src;
> @@ -649,7 +660,8 @@ static int do_dump(int argc, char **argv)
>   			err = -ENOTSUP;
>   			goto done;
>   		}
> -		err = dump_btf_c(btf, root_type_ids, root_type_cnt);
> +		err = dump_btf_c(btf, root_type_ids, root_type_cnt,
> +				 orig_argc, orig_argv);
>   	} else {
>   		err = dump_btf_raw(btf, root_type_ids, root_type_cnt);
>   	}
> --
> 2.25.1