netdev - Re: [PATCH bpf-next v4 3/8] bpftool: Add gen btf command

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Date:   Fri, 14 Jan 2022 18:09:38 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Mauricio Vásquez <mauricio@...volk.io>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Rafael David Tinoco <rafaeldtinoco@...il.com>,
        Lorenzo Fontana <lorenzo.fontana@...stic.co>,
        Leonardo Di Donato <leonardo.didonato@...stic.co>
Subject: Re: [PATCH bpf-next v4 3/8] bpftool: Add gen btf command

On Wed, Jan 12, 2022 at 6:27 AM Mauricio Vásquez <mauricio@...volk.io> wrote:
>
> This command is implemented under the "gen" command in bpftool and the
> syntax is the following:
>
> $ bpftool gen btf INPUT OUTPUT OBJECT(S)

"gen btf" doesn't really convey that it's a minimized BTF for CO-RE,
maybe let's do something more verbose but also more precise, it's not
like this is going to be used by everyone multiple times a day, so
verboseness is not a bad thing here. Naming is hard, but something
like `bpftool gen min_core_btf` probably would give a bit better
pointer as to what this command is doing (minimal CO-RE BTF, right?)

>
> INPUT can be either a single BTF file or a folder containing BTF files,
> when it's a folder, a BTF file is generated for each BTF file contained
> in this folder. OUTPUT is the file (or folder) where generated files are
> stored and OBJECT(S) is the list of bpf objects we want to generate the
> BTF file(s) for (each generated BTF file contains all the types needed
> by all the objects).
>
> Signed-off-by: Mauricio Vásquez <mauricio@...volk.io>
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...asec.com>
> Signed-off-by: Lorenzo Fontana <lorenzo.fontana@...stic.co>
> Signed-off-by: Leonardo Di Donato <leonardo.didonato@...stic.co>
> ---
>  tools/bpf/bpftool/gen.c | 117 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 117 insertions(+)
>

[...]

> +
> +       while ((dir = readdir(d)) != NULL) {
> +               if (dir->d_type != DT_REG)
> +                       continue;
> +
> +               if (strncmp(dir->d_name + strlen(dir->d_name) - 4, ".btf", 4))
> +                       continue;
> +
> +               snprintf(src_btf_path, sizeof(src_btf_path), "%s/%s", input, dir->d_name);
> +               snprintf(dst_btf_path, sizeof(dst_btf_path), "%s/%s", output, dir->d_name);
> +
> +               printf("SBTF: %s\n", src_btf_path);

What's SBTF? Is this part of bpftool "protocol" now? It should be
something a bit more meaningful...

> +
> +               err = btfgen(src_btf_path, dst_btf_path, objs);
> +               if (err)
> +                       goto out;
> +       }
> +
> +out:
> +       if (!err)
> +               printf("STAT: done!\n");

similar, STAT? what's that? Do we need "done!" message in tool's output?

> +       free(objs);
> +       closedir(d);
> +       return err;
> +}
> +
>  static const struct cmd cmds[] = {
>         { "object",     do_object },
>         { "skeleton",   do_skeleton },
> +       { "btf",        do_gen_btf},
>         { "help",       do_help },
>         { 0 }
>  };
> --
> 2.25.1
>