On Thu, Feb 13, 2020 at 7:05 AM Eelco Chaudron <echaudro@xxxxxxxxxx> 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_expected_attach_type(prog, BPF_TRACE_FENTRY);
> bpf_program__set_attach_target(prog, xdp_fd,
> "xdpfilt_blk_all");
> bpf_object__load(trace_obj)
>
> Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
> ---
API-wise this looks good, thanks! Please address feedback below and
re-submit once bpf-next opens. Can you please also convert one of
existing selftests using open_opts's attach_prog_fd to use this API
instead to have a demonstration there?
> v1 -> v2: Remove requirement for attach type name in API
>
> tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++++++--
> tools/lib/bpf/libbpf.h | 4 ++++
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 514b1a524abb..9b8cab995580 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4939,8 +4939,8 @@ 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) {
> + 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);
> if (btf_id <= 0)
> return btf_id;
> @@ -8132,6 +8132,35 @@ void bpf_program__bpil_offs_to_addr(struct bpf_prog_info_linear *info_linear)
> }
> }
>
> +int bpf_program__set_attach_target(struct bpf_program *prog,
> + int attach_prog_fd,
> + const char *attach_func_name)
> +{
> + int btf_id;
> +
> + if (!prog || attach_prog_fd < 0 || !attach_func_name)
> + return -EINVAL;
> +
> + if (attach_prog_fd)
> + btf_id = libbpf_find_prog_btf_id(attach_func_name,
> + attach_prog_fd);
> + else
> + btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
> + attach_func_name,
> + prog->expected_attach_type);
> +
> + if (btf_id <= 0) {
> + if (!attach_prog_fd)
> + pr_warn("%s is not found in vmlinux BTF\n",
> + attach_func_name);
libbpf_find_attach_btf_id's error reporting is misleading (it always
reports as if error happened with vmlinux BTF, even if attach_prog_fd
> 0). Could you please fix that and add better error reporting here
for attach_prog_fd>0 case here?
> + return btf_id;
> + }
> +
> + prog->attach_btf_id = btf_id;
> + prog->attach_prog_fd = attach_prog_fd;
> + return 0;
> +}
> +
> int parse_cpu_mask_str(const char *s, bool **mask, int *mask_sz)
> {
> int err = 0, n, len, start, end = -1;
> 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;
This will have to go into LIBBPF_0.0.8 once bpf-next opens. Please
rebase and re-send then.
> bpf_program__set_extension;
> bpf_program__set_struct_ops;
> btf__align_of;
>
