[PATCH bpf-next 4/5] libbpf: add the function libbpf_find_kernel_btf_id()

[Menglong Dong]

Add new function libbpf_find_kernel_btf_id() to find the btf type id of
the kernel, including vmlinux and modules.

Signed-off-by: Menglong Dong <dongmenglong.8@xxxxxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c   | 83 ++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  3 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 87 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 01f407591a92..44e34007de8c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9500,6 +9500,89 @@ int libbpf_find_vmlinux_btf_id(const char *name,
 	return libbpf_err(err);
 }
 
+int libbpf_find_kernel_btf_id(const char *name,
+			      enum bpf_attach_type attach_type,
+			      int *btf_obj_fd, int *btf_type_id)
+{
+	struct btf *btf, *vmlinux_btf;
+	struct bpf_btf_info info;
+	__u32 btf_id = 0, len;
+	char btf_name[64];
+	int err, fd;
+
+	vmlinux_btf = btf__load_vmlinux_btf();
+	err = libbpf_get_error(vmlinux_btf);
+	if (err)
+		return libbpf_err(err);
+
+	err = find_attach_btf_id(vmlinux_btf, name, attach_type);
+	if (err > 0) {
+		*btf_type_id = err;
+		*btf_obj_fd = 0;
+		err = 0;
+		goto out;
+	}
+
+	/* kernel too old to support module BTFs */
+	if (!feat_supported(NULL, FEAT_MODULE_BTF)) {
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
+	while (true) {
+		err = bpf_btf_get_next_id(btf_id, &btf_id);
+		if (err) {
+			err = -errno;
+			goto out;
+		}
+
+		fd = bpf_btf_get_fd_by_id(btf_id);
+		if (fd < 0) {
+			if (errno == ENOENT)
+				continue;
+			err = -errno;
+			goto out;
+		}
+
+		len = sizeof(info);
+		memset(&info, 0, sizeof(info));
+		info.name = ptr_to_u64(btf_name);
+		info.name_len = sizeof(btf_name);
+
+		err = bpf_btf_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			err = -errno;
+			goto fd_out;
+		}
+
+		if (!info.kernel_btf || strcmp(btf_name, "vmlinux") == 0) {
+			close(fd);
+			continue;
+		}
+
+		btf = btf_get_from_fd(fd, vmlinux_btf);
+		err = libbpf_get_error(btf);
+		if (err)
+			goto fd_out;
+
+		err = find_attach_btf_id(btf, name, attach_type);
+		if (err > 0) {
+			*btf_type_id = err;
+			*btf_obj_fd = fd;
+			err = 0;
+			break;
+		}
+		close(fd);
+		continue;
+fd_out:
+		close(fd);
+		break;
+	}
+out:
+	btf__free(vmlinux_btf);
+	return err;
+}
+
 static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 {
 	struct bpf_prog_info info;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5723cbbfcc41..ca151bbec833 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -306,6 +306,9 @@ LIBBPF_API int libbpf_attach_type_by_name(const char *name,
 					  enum bpf_attach_type *attach_type);
 LIBBPF_API int libbpf_find_vmlinux_btf_id(const char *name,
 					  enum bpf_attach_type attach_type);
+LIBBPF_API int libbpf_find_kernel_btf_id(const char *name,
+					 enum bpf_attach_type attach_type,
+					 int *btf_obj_fd, int *btf_type_id);
 
 /* Accessors of bpf_program */
 struct bpf_program;
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 86804fd90dd1..73c60f47b4bb 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -413,4 +413,5 @@ LIBBPF_1.4.0 {
 		bpf_token_create;
 		btf__new_split;
 		btf_ext__raw_data;
+		libbpf_find_kernel_btf_id;
 } LIBBPF_1.3.0;
-- 
2.39.2