linux-kernel - Re: [PATCH bpf-next v4 0/3] Add btf_custom_path in bpf_obj_open

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Date:   Thu, 15 Jul 2021 21:49:41 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Shuyi Cheng <chengshuyi@...ux.alibaba.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 0/3] Add btf_custom_path in bpf_obj_open_opts

On Tue, Jul 13, 2021 at 5:43 AM Shuyi Cheng
<chengshuyi@...ux.alibaba.com> wrote:
>
> This patch set adds the ability to point to a custom BTF for the
> purposes of BPF CO-RE relocations. This is useful for using BPF CO-RE
> on old kernels that don't yet natively support kernel (vmlinux) BTF
> and thus libbpf needs application's help in locating kernel BTF
> generated separately from the kernel itself. This was already possible
> to do through bpf_object__load's attribute struct, but that makes it
> inconvenient to use with BPF skeleton, which only allows to specify
> bpf_object_open_opts during the open step. Thus, add the ability to
> override vmlinux BTF at open time.
>
> Patch #1 adds libbpf changes.
> Patch #2 fixes pre-existing memory leak detected during the code review.
> Patch #3 switches existing selftests to using open_opts for custom BTF.
>

LGTM with some minor things I'll adjust while applying (which I'll
point out in respective patches). So no need to re-send anything.
Thanks.

> Changelog:
> ----------
>
> v3: https://lore.kernel.org/bpf/CAEf4BzY2cdT44bfbMus=gei27ViqGE1BtGo6XrErSsOCnqtVJg@mail.gmail.com/T/#m877eed1d4cf0a1d3352d3f3d6c5ff158be45c542
> v3->v4:
> --- Follow Andrii's suggestion to modify cover letter description.
> --- Delete function bpf_object__load_override_btf.
> --- Follow Dan's suggestion to add fixes tag and modify commit msg to patch #2.
> --- Add pathch #3 to switch existing selftests to using open_opts.
>
> v2: https://lore.kernel.org/bpf/CAEf4Bza_ua+tjxdhyy4nZ8Boeo+scipWmr_1xM1pC6N5wyuhAA@mail.gmail.com/T/#mf9cf86ae0ffa96180ac29e4fd12697eb70eccd0f
> v2->v3:
> --- Load the BTF specified by btf_custom_path to btf_vmlinux_override
>     instead of btf_bmlinux.
> --- Fix the memory leak that may be introduced by the second version
>     of the patch.
> --- Add a new patch to fix the possible memory leak caused by
>     obj->kconfig.
>
> v1: https://lore.kernel.org/bpf/CAEf4BzaGjEC4t1OefDo11pj2-HfNy0BLhs_G2UREjRNTmb2u=A@mail.gmail.com/t/#m4d9f7c6761fbd2b436b5dfe491cd864b70225804
> v1->v2:
> -- Change custom_btf_path to btf_custom_path.
> -- If the length of btf_custom_path of bpf_obj_open_opts is too long,
>    return ERR_PTR(-ENAMETOOLONG).
> -- Add `custom BTF is in addition to vmlinux BTF`
>    with btf_custom_path field.
>
> Shuyi Cheng (3):
>   libbpf: Introduce 'btf_custom_path' to 'bpf_obj_open_opts'
>   libbpf: Fix the possible memory leak on error
>   selftests/bpf: switches existing selftests to using open_opts for custom BTF
>
>  tools/lib/bpf/libbpf.c                             | 42 +++++++++++++++++-----
>  tools/lib/bpf/libbpf.h                             |  9 ++++-
>  .../selftests/bpf/prog_tests/core_autosize.c       | 22 ++++++------
>  .../testing/selftests/bpf/prog_tests/core_reloc.c  | 28 +++++++--------
>  4 files changed, 66 insertions(+), 35 deletions(-)
>
> --
> 1.8.3.1
>