netdev - Re: [PATCH] libbpf: Support raw btf placed in the default path

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Date:   Fri, 9 Sep 2022 12:00:24 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Tao Chen <chentao.kernel@...ux.alibaba.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: Support raw btf placed in the default path

On Sun, Aug 28, 2022 at 10:36 PM Tao Chen
<chentao.kernel@...ux.alibaba.com> wrote:
>
> Hi Nakryiko, thank you for your reply. Yes, i happed to put the raw
> BTF made by myself in /boot on kernel4.19, unluckly it reported error.
> So is it possible to allow the raw BTF in /boot directly, athough we
> can set the specified btf location again to solve the problem with the
> bpf_object_open_opts interface.
>
> As you say, maybe we can remove the locations[i].raw_btf check, just
> use the btf__parse, It looks more concise.

Please don't top post, reply inline (that's kernel mail lists rules).

But yes, I think we can just use btf__parse and let libbpf figure out.
Please send a patch.

>
> 在 2022/8/26 上午4:26, Andrii Nakryiko 写道:
>
> On Wed, Aug 24, 2022 at 7:05 AM chentao.ct
> <chentao.kernel@...ux.alibaba.com> wrote:
>
> Now only elf btf can be placed in the default path, raw btf should
> also can be there.
>
> It's not clear what you are trying to achieve. Do you want libbpf to
> attempt to load /boot/vmlinux-%1$s as raw BTF as well (so you can sort
> of sneak in pregenerated BTF), or what exactly?
> btf__load_vmlinux_btf() code already supports loading raw BTF, it just
> needs to be explicitly specified in locations table.
>
> So with your change locations[i].raw_btf check doesn't make sense and
> we need to clean this up.
>
> But first, let's discuss the use case, instead of your specific solution.
>
>
> Signed-off-by: chentao.ct <chentao.kernel@...ux.alibaba.com>
> ---
>  tools/lib/bpf/btf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index bb1e06e..b22b5b3 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -4661,7 +4661,7 @@ struct btf *btf__load_vmlinux_btf(void)
>         } locations[] = {
>                 /* try canonical vmlinux BTF through sysfs first */
>                 { "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
> -               /* fall back to trying to find vmlinux ELF on disk otherwise */
> +               /* fall back to trying to find vmlinux RAW/ELF on disk otherwise */
>                 { "/boot/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/vmlinux-%1$s" },
>                 { "/lib/modules/%1$s/build/vmlinux" },
> @@ -4686,7 +4686,7 @@ struct btf *btf__load_vmlinux_btf(void)
>                 if (locations[i].raw_btf)
>                         btf = btf__parse_raw(path);
>                 else
> -                       btf = btf__parse_elf(path, NULL);
> +                       btf = btf__parse(path, NULL);
>                 err = libbpf_get_error(btf);
>                 pr_debug("loading kernel BTF '%s': %d\n", path, err);
>                 if (err)
> --
> 2.2.1
>