libbpf: Add support for dynamic program attach target

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@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158220519486.127661.7964708960649051384.stgit@xdp-tutorial

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 0eb10b6..8f0c436 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4937,8 +4937,8 @@ 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;
@@ -6581,6 +6581,9 @@ static inline int __find_vmlinux_btf_id(struct btf *btf, const char *name,
        else
                err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
 
+       if (err <= 0)
+               pr_warn("%s is not found in vmlinux BTF\n", name);
+
        return err;
 }
 
@@ -6653,8 +6656,6 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog)
                        err = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
                                                    name + section_defs[i].len,
                                                    attach_type);
-               if (err <= 0)
-                       pr_warn("%s is not found in vmlinux BTF\n", name);
                return err;
        }
        pr_warn("failed to identify btf_id based on ELF section name '%s'\n", name);
@@ -8130,6 +8131,31 @@ 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)
+               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 3fe12c9..02fc58a 100644 (file)
--- 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 45be19c..7b014c8 100644 (file)
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -237,4 +237,6 @@ LIBBPF_0.0.7 {
 } LIBBPF_0.0.6;
 
 LIBBPF_0.0.8 {
+       global:
+               bpf_program__set_attach_target;
 } LIBBPF_0.0.7;