Merge branch 'libbpf: rename btf__get_from_id() and btf__load() APIs, support split BTF'

Quentin Monnet says:

====================

As part of the effort to move towards a v1.0 for libbpf [0], this set
improves some confusing function names related to BTF loading from and to
the kernel:

- btf__load() becomes btf__load_into_kernel().
- btf__get_from_id becomes btf__load_from_kernel_by_id().
- A new version btf__load_from_kernel_by_id_split() extends the former to
  add support for split BTF.

The last patch is a trivial change to bpftool to add support for dumping
split BTF objects by referencing them by their id (and not only by their
BTF path).

[0] https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#btfh-apis

v3:
- Use libbpf_err_ptr() in btf__load_from_kernel_by_id(), ERR_PTR() in
  bpftool's get_map_kv_btf().
- Move the definition of btf__load_from_kernel_by_id() closer to the
  btf__parse() group in btf.h (move the legacy function with it).
- Fix a bug on the return value in libbpf_find_prog_btf_id(), as a new
  patch.
- Move the btf__free() fixes to their own patch.
- Add "Fixes:" tags to relevant patches.

v2:
- Remove deprecation marking of legacy functions (patch 4/6 from v1).
- Make btf__load_from_kernel_by_id{,_split}() return the btf struct, adjust
  surrounding code and call btf__free() when missing.
- Add new functions to v0.5.0 API (and not v0.6.0).
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/bpf/bpftool/btf.c

@@ -580,16 +580,12 @@ static int do_dump(int argc, char **argv)
 	}
 
 	if (!btf) {
-		err = btf__get_from_id(btf_id, &btf);
+		btf = btf__load_from_kernel_by_id_split(btf_id, base_btf);
+		err = libbpf_get_error(btf);
 		if (err) {
 			p_err("get btf by id (%u): %s", btf_id, strerror(err));
 			goto done;
 		}
-		if (!btf) {
-			err = -ENOENT;
-			p_err("can't find btf with ID (%u)", btf_id);
-			goto done;
-		}
 	}
 
 	if (dump_c) {

tools/bpf/bpftool/btf_dumper.c

@@ -64,8 +64,10 @@ static int dump_prog_id_as_func_ptr(const struct btf_dumper *d,
 	}
 	info = &prog_info->info;
 
-	if (!info->btf_id || !info->nr_func_info ||
-	    btf__get_from_id(info->btf_id, &prog_btf))
+	if (!info->btf_id || !info->nr_func_info)
+		goto print;
+	prog_btf = btf__load_from_kernel_by_id(info->btf_id);
+	if (libbpf_get_error(prog_btf))
 		goto print;
 	finfo = u64_to_ptr(info->func_info);
 	func_type = btf__type_by_id(prog_btf, finfo->type_id);

tools/bpf/bpftool/map.c

@@ -807,10 +807,11 @@ static struct btf *get_map_kv_btf(const struct bpf_map_info *info)
 	} else if (info->btf_value_type_id) {
 		int err;
 
-		err = btf__get_from_id(info->btf_id, &btf);
-		if (err || !btf) {
+		btf = btf__load_from_kernel_by_id(info->btf_id);
+		err = libbpf_get_error(btf);
+		if (err) {
 			p_err("failed to get btf");
-			btf = err ? ERR_PTR(err) : ERR_PTR(-ESRCH);
+			btf = ERR_PTR(err);
 		}
 	}
 
@@ -1039,11 +1040,10 @@ static void print_key_value(struct bpf_map_info *info, void *key,
 			    void *value)
 {
 	json_writer_t *btf_wtr;
-	struct btf *btf = NULL;
-	int err;
+	struct btf *btf;
 
-	err = btf__get_from_id(info->btf_id, &btf);
-	if (err) {
+	btf = btf__load_from_kernel_by_id(info->btf_id);
+	if (libbpf_get_error(btf)) {
 		p_err("failed to get btf");
 		return;
 	}

tools/bpf/bpftool/prog.c

@@ -249,10 +249,10 @@ static void show_prog_metadata(int fd, __u32 num_maps)
 	struct bpf_map_info map_info;
 	struct btf_var_secinfo *vsi;
 	bool printed_header = false;
-	struct btf *btf = NULL;
 	unsigned int i, vlen;
 	void *value = NULL;
 	const char *name;
+	struct btf *btf;
 	int err;
 
 	if (!num_maps)
@@ -263,8 +263,8 @@ static void show_prog_metadata(int fd, __u32 num_maps)
 	if (!value)
 		return;
 
-	err = btf__get_from_id(map_info.btf_id, &btf);
-	if (err || !btf)
+	btf = btf__load_from_kernel_by_id(map_info.btf_id);
+	if (libbpf_get_error(btf))
 		goto out_free;
 
 	t_datasec = btf__type_by_id(btf, map_info.btf_value_type_id);
@@ -646,9 +646,12 @@ prog_dump(struct bpf_prog_info *info, enum dump_mode mode,
 		member_len = info->xlated_prog_len;
 	}
 
-	if (info->btf_id && btf__get_from_id(info->btf_id, &btf)) {
-		p_err("failed to get btf");
-		return -1;
+	if (info->btf_id) {
+		btf = btf__load_from_kernel_by_id(info->btf_id);
+		if (libbpf_get_error(btf)) {
+			p_err("failed to get btf");
+			return -1;
+		}
 	}
 
 	func_info = u64_to_ptr(info->func_info);
@@ -781,6 +784,8 @@ prog_dump(struct bpf_prog_info *info, enum dump_mode mode,
 		kernel_syms_destroy(&dd);
 	}
 
+	btf__free(btf);
+
 	return 0;
 }
 
@@ -2002,8 +2007,8 @@ static char *profile_target_name(int tgt_fd)
 	struct bpf_prog_info_linear *info_linear;
 	struct bpf_func_info *func_info;
 	const struct btf_type *t;
+	struct btf *btf = NULL;
 	char *name = NULL;
-	struct btf *btf;
 
 	info_linear = bpf_program__get_prog_info_linear(
 		tgt_fd, 1UL << BPF_PROG_INFO_FUNC_INFO);
@@ -2012,12 +2017,17 @@ static char *profile_target_name(int tgt_fd)
 		return NULL;
 	}
 
-	if (info_linear->info.btf_id == 0 ||
-	    btf__get_from_id(info_linear->info.btf_id, &btf)) {
+	if (info_linear->info.btf_id == 0) {
 		p_err("prog FD %d doesn't have valid btf", tgt_fd);
 		goto out;
 	}
 
+	btf = btf__load_from_kernel_by_id(info_linear->info.btf_id);
+	if (libbpf_get_error(btf)) {
+		p_err("failed to load btf for prog FD %d", tgt_fd);
+		goto out;
+	}
+
 	func_info = u64_to_ptr(info_linear->info.func_info);
 	t = btf__type_by_id(btf, func_info[0].type_id);
 	if (!t) {
@@ -2027,6 +2037,7 @@ static char *profile_target_name(int tgt_fd)
 	}
 	name = strdup(btf__name_by_offset(btf, t->name_off));
 out:
+	btf__free(btf);
 	free(info_linear);
 	return name;
 }

tools/lib/bpf/btf.c

@@ -1180,7 +1180,7 @@ int btf__finalize_data(struct bpf_object *obj, struct btf *btf)
 
 static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian);
 
-int btf__load(struct btf *btf)
+int btf__load_into_kernel(struct btf *btf)
 {
 	__u32 log_buf_size = 0, raw_size;
 	char *log_buf = NULL;
@@ -1228,6 +1228,7 @@ done:
 	free(log_buf);
 	return libbpf_err(err);
 }
+int btf__load(struct btf *) __attribute__((alias("btf__load_into_kernel")));
 
 int btf__fd(const struct btf *btf)
 {
@@ -1382,21 +1383,35 @@ exit_free:
 	return btf;
 }
 
+struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf)
+{
+	struct btf *btf;
+	int btf_fd;
+
+	btf_fd = bpf_btf_get_fd_by_id(id);
+	if (btf_fd < 0)
+		return libbpf_err_ptr(-errno);
+
+	btf = btf_get_from_fd(btf_fd, base_btf);
+	close(btf_fd);
+
+	return libbpf_ptr(btf);
+}
+
+struct btf *btf__load_from_kernel_by_id(__u32 id)
+{
+	return btf__load_from_kernel_by_id_split(id, NULL);
+}
+
 int btf__get_from_id(__u32 id, struct btf **btf)
 {
 	struct btf *res;
-	int err, btf_fd;
+	int err;
 
 	*btf = NULL;
-	btf_fd = bpf_btf_get_fd_by_id(id);
-	if (btf_fd < 0)
-		return libbpf_err(-errno);
-
-	res = btf_get_from_fd(btf_fd, NULL);
+	res = btf__load_from_kernel_by_id(id);
 	err = libbpf_get_error(res);
 
-	close(btf_fd);
-
 	if (err)
 		return libbpf_err(err);
 

tools/lib/bpf/btf.h

@@ -44,8 +44,13 @@ LIBBPF_API struct btf *btf__parse_elf_split(const char *path, struct btf *base_b
 LIBBPF_API struct btf *btf__parse_raw(const char *path);
 LIBBPF_API struct btf *btf__parse_raw_split(const char *path, struct btf *base_btf);
 
+LIBBPF_API struct btf *btf__load_from_kernel_by_id(__u32 id);
+LIBBPF_API struct btf *btf__load_from_kernel_by_id_split(__u32 id, struct btf *base_btf);
+LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
+
 LIBBPF_API int btf__finalize_data(struct bpf_object *obj, struct btf *btf);
 LIBBPF_API int btf__load(struct btf *btf);
+LIBBPF_API int btf__load_into_kernel(struct btf *btf);
 LIBBPF_API __s32 btf__find_by_name(const struct btf *btf,
 				   const char *type_name);
 LIBBPF_API __s32 btf__find_by_name_kind(const struct btf *btf,
@@ -66,7 +71,6 @@ LIBBPF_API void btf__set_fd(struct btf *btf, int fd);
 LIBBPF_API const void *btf__get_raw_data(const struct btf *btf, __u32 *size);
 LIBBPF_API const char *btf__name_by_offset(const struct btf *btf, __u32 offset);
 LIBBPF_API const char *btf__str_by_offset(const struct btf *btf, __u32 offset);
-LIBBPF_API int btf__get_from_id(__u32 id, struct btf **btf);
 LIBBPF_API int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 				    __u32 expected_key_size,
 				    __u32 expected_value_size,

tools/lib/bpf/libbpf.c

@@ -2769,7 +2769,7 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
 		 */
 		btf__set_fd(kern_btf, 0);
 	} else {
-		err = btf__load(kern_btf);
+		err = btf__load_into_kernel(kern_btf);
 	}
 	if (sanitize) {
 		if (!err) {
@@ -8316,8 +8316,8 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 {
 	struct bpf_prog_info_linear *info_linear;
 	struct bpf_prog_info *info;
-	struct btf *btf = NULL;
-	int err = -EINVAL;
+	struct btf *btf;
+	int err;
 
 	info_linear = bpf_program__get_prog_info_linear(attach_prog_fd, 0);
 	err = libbpf_get_error(info_linear);
@@ -8326,12 +8326,15 @@ static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 			attach_prog_fd);
 		return err;
 	}
+
+	err = -EINVAL;
 	info = &info_linear->info;
 	if (!info->btf_id) {
 		pr_warn("The target program doesn't have BTF\n");
 		goto out;
 	}
-	if (btf__get_from_id(info->btf_id, &btf)) {
+	btf = btf__load_from_kernel_by_id(info->btf_id);
+	if (libbpf_get_error(btf)) {
 		pr_warn("Failed to get BTF of the program\n");
 		goto out;
 	}

tools/lib/bpf/libbpf.map

@@ -375,6 +375,9 @@ LIBBPF_0.5.0 {
 		bpf_map_lookup_and_delete_elem_flags;
 		bpf_program__attach_kprobe_opts;
 		bpf_object__gen_loader;
+		btf__load_from_kernel_by_id;
+		btf__load_from_kernel_by_id_split;
+		btf__load_into_kernel;
 		btf_dump__dump_type_data;
 		libbpf_set_strict_mode;
 } LIBBPF_0.4.0;

tools/perf/util/bpf-event.c

@@ -223,10 +223,10 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_session *session,
 			free(info_linear);
 			return -1;
 		}
-		if (btf__get_from_id(info->btf_id, &btf)) {
+		btf = btf__load_from_kernel_by_id(info->btf_id);
+		if (libbpf_get_error(btf)) {
 			pr_debug("%s: failed to get BTF of id %u, aborting\n", __func__, info->btf_id);
 			err = -1;
-			btf = NULL;
 			goto out;
 		}
 		perf_env__fetch_btf(env, info->btf_id, btf);
@@ -296,7 +296,7 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_session *session,
 
 out:
 	free(info_linear);
-	free(btf);
+	btf__free(btf);
 	return err ? -1 : 0;
 }
 
@@ -478,7 +478,8 @@ static void perf_env__add_bpf_info(struct perf_env *env, u32 id)
 	if (btf_id == 0)
 		goto out;
 
-	if (btf__get_from_id(btf_id, &btf)) {
+	btf = btf__load_from_kernel_by_id(btf_id);
+	if (libbpf_get_error(btf)) {
 		pr_debug("%s: failed to get BTF of id %u, aborting\n",
 			 __func__, btf_id);
 		goto out;
@@ -486,7 +487,7 @@ static void perf_env__add_bpf_info(struct perf_env *env, u32 id)
 	perf_env__fetch_btf(env, btf_id, btf);
 
 out:
-	free(btf);
+	btf__free(btf);
 	close(fd);
 }
 

tools/perf/util/bpf_counter.c

@@ -64,8 +64,8 @@ static char *bpf_target_prog_name(int tgt_fd)
 	struct bpf_prog_info_linear *info_linear;
 	struct bpf_func_info *func_info;
 	const struct btf_type *t;
+	struct btf *btf = NULL;
 	char *name = NULL;
-	struct btf *btf;
 
 	info_linear = bpf_program__get_prog_info_linear(
 		tgt_fd, 1UL << BPF_PROG_INFO_FUNC_INFO);
@@ -74,12 +74,17 @@ static char *bpf_target_prog_name(int tgt_fd)
 		return NULL;
 	}
 
-	if (info_linear->info.btf_id == 0 ||
-	    btf__get_from_id(info_linear->info.btf_id, &btf)) {
+	if (info_linear->info.btf_id == 0) {
 		pr_debug("prog FD %d doesn't have valid btf\n", tgt_fd);
 		goto out;
 	}
 
+	btf = btf__load_from_kernel_by_id(info_linear->info.btf_id);
+	if (libbpf_get_error(btf)) {
+		pr_debug("failed to load btf for prog FD %d\n", tgt_fd);
+		goto out;
+	}
+
 	func_info = u64_to_ptr(info_linear->info.func_info);
 	t = btf__type_by_id(btf, func_info[0].type_id);
 	if (!t) {
@@ -89,6 +94,7 @@ static char *bpf_target_prog_name(int tgt_fd)
 	}
 	name = strdup(btf__name_by_offset(btf, t->name_off));
 out:
+	btf__free(btf);
 	free(info_linear);
 	return name;
 }

tools/testing/selftests/bpf/prog_tests/btf.c

@@ -4350,7 +4350,8 @@ static void do_test_file(unsigned int test_num)
 		goto done;
 	}
 
-	err = btf__get_from_id(info.btf_id, &btf);
+	btf = btf__load_from_kernel_by_id(info.btf_id);
+	err = libbpf_get_error(btf);
 	if (CHECK(err, "cannot get btf from kernel, err: %d", err))
 		goto done;
 
@@ -4386,6 +4387,7 @@ skip:
 	fprintf(stderr, "OK");
 
 done:
+	btf__free(btf);
 	free(func_info);
 	bpf_object__close(obj);
 }