netdev - Re: [PATCH bpf-next 4/7] libbpf: Add support to attach to fentry/fexit tracing progs

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Message-ID: <CAEf4BzbJ3Y4_rjvr9Xu2MR87Ghdx_1n=KOOaeqM_F7+OwPihRw@mail.gmail.com>
Date:   Tue, 5 Nov 2019 13:17:54 -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>,
        Peter Ziljstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 4/7] libbpf: Add support to attach to
 fentry/fexit tracing progs

On Sat, Nov 2, 2019 at 3:03 PM Alexei Starovoitov <ast@...nel.org> wrote:
>
> Teach libbpf to recognize tracing programs types and attach them to
> fentry/fexit.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  tools/include/uapi/linux/bpf.h |  2 ++
>  tools/lib/bpf/libbpf.c         | 55 +++++++++++++++++++++++++++++-----
>  tools/lib/bpf/libbpf.h         |  2 ++
>  tools/lib/bpf/libbpf.map       |  1 +
>  4 files changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index df6809a76404..69c200e6e696 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -201,6 +201,8 @@ enum bpf_attach_type {
>         BPF_CGROUP_GETSOCKOPT,
>         BPF_CGROUP_SETSOCKOPT,
>         BPF_TRACE_RAW_TP,
> +       BPF_TRACE_FENTRY,
> +       BPF_TRACE_FEXIT,
>         __MAX_BPF_ATTACH_TYPE
>  };
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7aa2a2a22cef..03e784f36dd9 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3744,7 +3744,7 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
>         return 0;
>  }
>
> -static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id);
> +static int libbpf_attach_btf_id_by_name(const char *name, __u32 *btf_id, bool raw_tp);

Bools are hard to follow in code, why not just passing full
attach_type instead? It will also be more future-proof, if we need
another trick, similar to "bpf_trace_" prefix for raw_tp?

Also, I have a mild preference for having output arguments to be the
very last in the argument list. Do you mind reordering so thar bool
raw_tp is second?

>
>  static struct bpf_object *
>  __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
> @@ -3811,7 +3811,9 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
>                 bpf_program__set_type(prog, prog_type);
>                 bpf_program__set_expected_attach_type(prog, attach_type);
>                 if (prog_type == BPF_PROG_TYPE_TRACING) {
> -                       err = libbpf_attach_btf_id_by_name(prog->section_name, &btf_id);
> +                       err = libbpf_attach_btf_id_by_name(prog->section_name,
> +                                                          &btf_id,
> +                                                          attach_type == BPF_TRACE_RAW_TP);

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