libbpf: Add OPTS-based bpf_btf_load() API

Similar to previous bpf_prog_load() and bpf_map_create() APIs, add
bpf_btf_load() API which is taking optional OPTS struct. Schedule
bpf_load_btf() for deprecation in v0.8 ([0]).

This makes naming consistent with BPF_BTF_LOAD command, sets up an API
for extensibility in the future, moves options parameters (log-related
fields) into optional options, and also allows to pass log_level
directly.

It also removes log buffer auto-allocation logic from low-level API
(consistent with bpf_prog_load() behavior), but preserves a special
treatment of log_level == 0 with non-NULL log_buf, which matches
low-level bpf_prog_load() and high-level libbpf APIs for BTF and program
loading behaviors.

  [0] Closes: https://github.com/libbpf/libbpf/issues/419Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211209193840.1248570-3-andrii@kernel.org

tools/lib/bpf/bpf.c

@@ -1047,24 +1047,65 @@ int bpf_raw_tracepoint_open(const char *name, int prog_fd)
 	return libbpf_err_errno(fd);
 }
 
-int bpf_load_btf(const void *btf, __u32 btf_size, char *log_buf, __u32 log_buf_size,
-		 bool do_log)
+int bpf_btf_load(const void *btf_data, size_t btf_size, const struct bpf_btf_load_opts *opts)
 {
-	union bpf_attr attr = {};
+	const size_t attr_sz = offsetofend(union bpf_attr, btf_log_level);
+	union bpf_attr attr;
+	char *log_buf;
+	size_t log_size;
+	__u32 log_level;
 	int fd;
 
-	attr.btf = ptr_to_u64(btf);
+	memset(&attr, 0, attr_sz);
+
+	if (!OPTS_VALID(opts, bpf_btf_load_opts))
+		return libbpf_err(-EINVAL);
+
+	log_buf = OPTS_GET(opts, log_buf, NULL);
+	log_size = OPTS_GET(opts, log_size, 0);
+	log_level = OPTS_GET(opts, log_level, 0);
+
+	if (log_size > UINT_MAX)
+		return libbpf_err(-EINVAL);
+	if (log_size && !log_buf)
+		return libbpf_err(-EINVAL);
+
+	attr.btf = ptr_to_u64(btf_data);
 	attr.btf_size = btf_size;
+	/* log_level == 0 and log_buf != NULL means "try loading without
+	 * log_buf, but retry with log_buf and log_level=1 on error", which is
+	 * consistent across low-level and high-level BTF and program loading
+	 * APIs within libbpf and provides a sensible behavior in practice
+	 */
+	if (log_level) {
+		attr.btf_log_buf = ptr_to_u64(log_buf);
+		attr.btf_log_size = (__u32)log_size;
+		attr.btf_log_level = log_level;
+	}
 
-retry:
-	if (do_log && log_buf && log_buf_size) {
-		attr.btf_log_level = 1;
-		attr.btf_log_size = log_buf_size;
+	fd = sys_bpf_fd(BPF_BTF_LOAD, &attr, attr_sz);
+	if (fd < 0 && log_buf && log_level == 0) {
 		attr.btf_log_buf = ptr_to_u64(log_buf);
+		attr.btf_log_size = (__u32)log_size;
+		attr.btf_log_level = 1;
+		fd = sys_bpf_fd(BPF_BTF_LOAD, &attr, attr_sz);
 	}
+	return libbpf_err_errno(fd);
+}
+
+int bpf_load_btf(const void *btf, __u32 btf_size, char *log_buf, __u32 log_buf_size, bool do_log)
+{
+	LIBBPF_OPTS(bpf_btf_load_opts, opts);
+	int fd;
 
-	fd = sys_bpf_fd(BPF_BTF_LOAD, &attr, sizeof(attr));
+retry:
+	if (do_log && log_buf && log_buf_size) {
+		opts.log_buf = log_buf;
+		opts.log_size = log_buf_size;
+		opts.log_level = 1;
+	}
 
+	fd = bpf_btf_load(btf, btf_size, &opts);
 	if (fd < 0 && !do_log && log_buf && log_buf_size) {
 		do_log = true;
 		goto retry;

tools/lib/bpf/bpf.h

@@ -213,6 +213,23 @@ LIBBPF_API int bpf_verify_program(enum bpf_prog_type type,
 				  char *log_buf, size_t log_buf_sz,
 				  int log_level);
 
+struct bpf_btf_load_opts {
+	size_t sz; /* size of this struct for forward/backward compatibility */
+
+	/* kernel log options */
+	char *log_buf;
+	__u32 log_level;
+	__u32 log_size;
+};
+#define bpf_btf_load_opts__last_field log_size
+
+LIBBPF_API int bpf_btf_load(const void *btf_data, size_t btf_size,
+			    const struct bpf_btf_load_opts *opts);
+
+LIBBPF_DEPRECATED_SINCE(0, 8, "use bpf_btf_load() instead")
+LIBBPF_API int bpf_load_btf(const void *btf, __u32 btf_size, char *log_buf,
+			    __u32 log_buf_size, bool do_log);
+
 LIBBPF_API int bpf_map_update_elem(int fd, const void *key, const void *value,
 				   __u64 flags);
 
@@ -340,8 +357,6 @@ LIBBPF_API int bpf_prog_query(int target_fd, enum bpf_attach_type type,
 			      __u32 query_flags, __u32 *attach_flags,
 			      __u32 *prog_ids, __u32 *prog_cnt);
 LIBBPF_API int bpf_raw_tracepoint_open(const char *name, int prog_fd);
-LIBBPF_API int bpf_load_btf(const void *btf, __u32 btf_size, char *log_buf,
-			    __u32 log_buf_size, bool do_log);
 LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf,
 				 __u32 *buf_len, __u32 *prog_id, __u32 *fd_type,
 				 __u64 *probe_offset, __u64 *probe_addr);

tools/lib/bpf/libbpf.map

@@ -422,6 +422,7 @@ LIBBPF_0.6.0 {
 
 LIBBPF_0.7.0 {
 	global:
+		bpf_btf_load;
 		bpf_program__log_level;
 		bpf_program__set_log_level;
 };

tools/lib/bpf/libbpf_probes.c

@@ -164,7 +164,7 @@ int libbpf__load_raw_btf(const char *raw_types, size_t types_len,
 	memcpy(raw_btf + hdr.hdr_len, raw_types, hdr.type_len);
 	memcpy(raw_btf + hdr.hdr_len + hdr.type_len, str_sec, hdr.str_len);
 
-	btf_fd = bpf_load_btf(raw_btf, btf_len, NULL, 0, false);
+	btf_fd = bpf_btf_load(raw_btf, btf_len, NULL);
 
 	free(raw_btf);
 	return btf_fd;