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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Eelco Chaudron <echaudro@redhat.com>
Cc: bpf <bpf@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Networking <netdev@vger.kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Martin Lau" <kafai@fb.com>, "Song Liu" <songliubraving@fb.com>,
	"Yonghong Song" <yhs@fb.com>, "Andrii Nakryiko" <andriin@fb.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>
Subject: Re: [PATCH bpf-next] libbpf: Add support for dynamic program attach target
Date: Wed, 12 Feb 2020 09:34:18 -0800
Message-ID: <CAEf4BzZqxQxWe5qawBOuDzvDpCHsmgfyqxWnackHd=hUQpz6bA@mail.gmail.com> (raw)
In-Reply-To: <158151067149.71757.2222114135650741733.stgit@xdp-tutorial>

On Wed, Feb 12, 2020 at 4:32 AM Eelco Chaudron <echaudro@redhat.com> wrote:
>
> Currently when you want to attach a trace program to a bpf program
> the section name needs to match the tracepoint/function semantics.
>
> However the addition of the bpf_program__set_attach_target() API
> allows you to specify the tracepoint/function dynamically.
>
> The call flow would look something like this:
>
>   xdp_fd = bpf_prog_get_fd_by_id(id);
>   trace_obj = bpf_object__open_file("func.o", NULL);
>   prog = bpf_object__find_program_by_title(trace_obj,
>                                            "fentry/myfunc");
>   bpf_program__set_attach_target(prog, xdp_fd,
>                                  "fentry/xdpfilt_blk_all");
>   bpf_object__load(trace_obj)
>
> Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
> ---
>  tools/lib/bpf/libbpf.c   |   41 +++++++++++++++++++++++++++++++++++------
>  tools/lib/bpf/libbpf.h   |    4 ++++
>  tools/lib/bpf/libbpf.map |    1 +
>  3 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 514b1a524abb..2ce879c301bb 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4933,15 +4933,16 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
>         return ret;
>  }
>
> -static int libbpf_find_attach_btf_id(struct bpf_program *prog);
> +static int libbpf_find_attach_btf_id(struct bpf_program *prog,
> +                                    const char *name);
>
>  int bpf_program__load(struct bpf_program *prog, char *license, __u32 kern_ver)
>  {
>         int err = 0, fd, i, btf_id;
>
> -       if (prog->type == BPF_PROG_TYPE_TRACING ||
> -           prog->type == BPF_PROG_TYPE_EXT) {
> -               btf_id = libbpf_find_attach_btf_id(prog);
> +       if ((prog->type == BPF_PROG_TYPE_TRACING ||
> +            prog->type == BPF_PROG_TYPE_EXT) && !prog->attach_btf_id) {
> +               btf_id = libbpf_find_attach_btf_id(prog, NULL);
>                 if (btf_id <= 0)
>                         return btf_id;
>                 prog->attach_btf_id = btf_id;
> @@ -6202,6 +6203,31 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
>         prog->expected_attach_type = type;
>  }
>
> +int bpf_program__set_attach_target(struct bpf_program *prog,
> +                                  int attach_prog_fd,
> +                                  const char *attach_func_name)
> +{
> +       __u32 org_attach_prog_fd;
> +       int btf_id;
> +
> +       if (!prog || attach_prog_fd < 0 || !attach_func_name)
> +               return -EINVAL;
> +
> +       org_attach_prog_fd = prog->attach_prog_fd;
> +       prog->attach_prog_fd = attach_prog_fd;
> +
> +       btf_id = libbpf_find_attach_btf_id(prog,
> +                                          attach_func_name);
> +
> +       if (btf_id < 0) {
> +               prog->attach_prog_fd = org_attach_prog_fd;

I don't think there is a need to restore original attach_prog_fd (most
probably it's going to be invalid either way). If explicit
set_attach_target fails, user application will have to fail or do some
other set_attach_target call.

> +               return btf_id;
> +       }
> +
> +       prog->attach_btf_id = btf_id;
> +       return 0;
> +}
> +
>  #define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
>         { string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
>
> @@ -6633,13 +6659,16 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
>         return err;
>  }
>
> -static int libbpf_find_attach_btf_id(struct bpf_program *prog)
> +static int libbpf_find_attach_btf_id(struct bpf_program *prog,
> +                                    const char *name)
>  {
>         enum bpf_attach_type attach_type = prog->expected_attach_type;
>         __u32 attach_prog_fd = prog->attach_prog_fd;
> -       const char *name = prog->section_name;
>         int i, err;
>
> +       if (!name)
> +               name = prog->section_name;
> +

I second Toke, name should be just a function name, not including
"fentry/" (and others) part. If user want to programmatically
set/override attach type, we already have
bpf_program__set_expected_attach_type() API for that. So this
function's logic should do prefix/name extraction from
prog->section_name only if name is not explicitly specified.

>         if (!name)
>                 return -EINVAL;
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 3fe12c9d1f92..02fc58a21a7f 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -334,6 +334,10 @@ LIBBPF_API void
>  bpf_program__set_expected_attach_type(struct bpf_program *prog,
>                                       enum bpf_attach_type type);
>
> +LIBBPF_API int
> +bpf_program__set_attach_target(struct bpf_program *prog, int attach_prog_fd,
> +                              const char *attach_func_name);
> +
>  LIBBPF_API bool bpf_program__is_socket_filter(const struct bpf_program *prog);
>  LIBBPF_API bool bpf_program__is_tracepoint(const struct bpf_program *prog);
>  LIBBPF_API bool bpf_program__is_raw_tracepoint(const struct bpf_program *prog);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index b035122142bb..8aba5438a3f0 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -230,6 +230,7 @@ LIBBPF_0.0.7 {
>                 bpf_program__name;
>                 bpf_program__is_extension;
>                 bpf_program__is_struct_ops;
> +               bpf_program__set_attach_target;
>                 bpf_program__set_extension;
>                 bpf_program__set_struct_ops;
>                 btf__align_of;
>

  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 12:31 Eelco Chaudron
2020-02-12 13:05 ` Toke Høiland-Jørgensen
2020-02-12 17:35   ` Andrii Nakryiko
2020-02-12 21:52     ` Toke Høiland-Jørgensen
2020-02-13 14:41       ` Eelco Chaudron
2020-02-12 17:34 ` Andrii Nakryiko [this message]
2020-02-12 17:56   ` Song Liu
2020-02-12 18:14     ` Andrii Nakryiko
2020-02-12 18:28       ` Song Liu
2020-02-12 18:34         ` Andrii Nakryiko
2020-02-12 18:40           ` Song Liu

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