Merge branch 'bpf: Show target_{obj,btf}_id for tracing link'

Yafang Shao says:

====================
The target_btf_id can help us understand which kernel function is
linked by a tracing prog. The target_btf_id and target_obj_id have
already been exposed to userspace, so we just need to show them.

For some other link types like perf_event and kprobe_multi, it is not
easy to find which functions are attached either. We may support
->fill_link_info for them in the future.

v1->v2:
- Skip showing them in the plain output for the old kernels. (Quentin)
- Coding improvement. (Andrii)
====================

Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/syscall.c

···
 {
 	struct bpf_tracing_link *tr_link =
 		container_of(link, struct bpf_tracing_link, link.link);
+	u32 target_btf_id, target_obj_id;
 
+	bpf_trampoline_unpack_key(tr_link->trampoline->key,
+				  &target_obj_id, &target_btf_id);
 	seq_printf(seq,
-		   "attach_type:\t%d\n",
-		   tr_link->attach_type);
+		   "attach_type:\t%d\n"
+		   "target_obj_id:\t%u\n"
+		   "target_btf_id:\t%u\n",
+		   tr_link->attach_type,
+		   target_obj_id,
+		   target_btf_id);
 }
 
 static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,

tools/bpf/bpftool/link.c

···
 
 		show_link_attach_type_json(info->tracing.attach_type,
 					   json_wtr);
+		jsonw_uint_field(json_wtr, "target_obj_id", info->tracing.target_obj_id);
+		jsonw_uint_field(json_wtr, "target_btf_id", info->tracing.target_btf_id);
 		break;
 	case BPF_LINK_TYPE_CGROUP:
 		jsonw_lluint_field(json_wtr, "cgroup_id",
···
 			printf("\n\tprog_type %u  ", prog_info.type);
 
 		show_link_attach_type_plain(info->tracing.attach_type);
+		if (info->tracing.target_obj_id || info->tracing.target_btf_id)
+			printf("\n\ttarget_obj_id %u  target_btf_id %u  ",
+			       info->tracing.target_obj_id,
+			       info->tracing.target_btf_id);
 		break;
 	case BPF_LINK_TYPE_CGROUP:
 		printf("\n\tcgroup_id %zu  ", (size_t)info->cgroup.cgroup_id);