On Wed, Feb 12, 2020 at 4:32 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_attach_target(prog, xdp_fd,
> "fentry/xdpfilt_blk_all");
> bpf_object__load(trace_obj)
>
> Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
> ---
> 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;
>
