netdev - Re: [PATCH bpf-next 2/3] libbpf: Add support for program extensions

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Date:   Mon, 20 Jan 2020 14:51:42 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/3] libbpf: Add support for program extensions

On Fri, Jan 17, 2020 at 4:47 PM Alexei Starovoitov <ast@...nel.org> wrote:
>
> Add minimal support for program extensions. bpf_object_open_opts() needs to be
> called with attach_prog_fd = target_prog_fd and BPF program extension needs to
> have in .c file section definition like SEC("replace/func_to_be_replaced").
> libbpf will search for "func_to_be_replaced" in the target_prog_fd's BTF and
> will pass it in attach_btf_id to the kernel. This approach works for tests, but
> more compex use case may need to request function name (and attach_btf_id that
> kernel sees) to be more dynamic. Such API will be added in future patches.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  tools/include/uapi/linux/bpf.h |  1 +
>  tools/lib/bpf/bpf.c            |  3 ++-
>  tools/lib/bpf/libbpf.c         | 14 +++++++++++---
>  tools/lib/bpf/libbpf.h         |  2 ++
>  tools/lib/bpf/libbpf.map       |  2 ++
>  tools/lib/bpf/libbpf_probes.c  |  1 +
>  6 files changed, 19 insertions(+), 4 deletions(-)
>

[...]

>  enum bpf_attach_type
>  bpf_program__get_expected_attach_type(struct bpf_program *prog)
> @@ -6265,6 +6269,10 @@ static const struct bpf_sec_def section_defs[] = {
>                 .expected_attach_type = BPF_TRACE_FEXIT,
>                 .is_attach_btf = true,
>                 .attach_fn = attach_trace),
> +       SEC_DEF("replace/", EXT,

how about freplace/, similar to fentry/fexit?

> +               .expected_attach_type = 0,

no need, it will be zero, if not specified here

> +               .is_attach_btf = true,
> +               .attach_fn = attach_trace),
>         BPF_PROG_SEC("xdp",                     BPF_PROG_TYPE_XDP),
>         BPF_PROG_SEC("perf_event",              BPF_PROG_TYPE_PERF_EVENT),
>         BPF_PROG_SEC("lwt_in",                  BPF_PROG_TYPE_LWT_IN),

[...]