Subject: [PATCH bpf-next v3 4/8] libbpf: implement bpf_prog_find_metadata

From: Stanislav Fomichev <[email-masked]>
Date: Fri, 28 Aug 2020 12:35:59 -0700

This is a low-level function (hence in bpf.c) to find out the metadata
map id for the provided program fd.
It will be used in the next commits from bpftool.

Cc: Toke Høiland-Jørgensen <[email-masked]>
Cc: YiFei Zhu <[email-masked]>
Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 tools/lib/bpf/bpf.c      | 74 ++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/bpf.h      |  1 +
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 76 insertions(+)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 5f6c5676cc45..01c0ede1625d 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -885,3 +885,77 @@ int bpf_prog_bind_map(int prog_fd, int map_fd,
 
 	return sys_bpf(BPF_PROG_BIND_MAP, &attr, sizeof(attr));
 }
+
+int bpf_prog_find_metadata(int prog_fd)
+{
+	struct bpf_prog_info prog_info = {};
+	struct bpf_map_info map_info;
+	__u32 prog_info_len;
+	__u32 map_info_len;
+	int saved_errno;
+	__u32 *map_ids;
+	int nr_maps;
+	int map_fd;
+	int ret;
+	int i;
+
+	prog_info_len = sizeof(prog_info);
+
+	ret = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &prog_info_len);
+	if (ret)
+		return ret;
+
+	if (!prog_info.nr_map_ids)
+		return -1;
+
+	map_ids = calloc(prog_info.nr_map_ids, sizeof(__u32));
+	if (!map_ids)
+		return -1;
+
+	nr_maps = prog_info.nr_map_ids;
+	memset(&prog_info, 0, sizeof(prog_info));
+	prog_info.nr_map_ids = nr_maps;
+	prog_info.map_ids = ptr_to_u64(map_ids);
+	prog_info_len = sizeof(prog_info);
+
+	ret = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &prog_info_len);
+	if (ret)
+		goto free_map_ids;
+
+	ret = -1;
+	for (i = 0; i < prog_info.nr_map_ids; i++) {
+		map_fd = bpf_map_get_fd_by_id(map_ids[i]);
+		if (map_fd < 0) {
+			ret = -1;
+			goto free_map_ids;
+		}
+
+		memset(&map_info, 0, sizeof(map_info));
+		map_info_len = sizeof(map_info);
+		ret = bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len);
+		saved_errno = errno;
+		close(map_fd);
+		errno = saved_errno;
+		if (ret)
+			goto free_map_ids;
+
+		if (map_info.type != BPF_MAP_TYPE_ARRAY)
+			continue;
+		if (map_info.key_size != sizeof(int))
+			continue;
+		if (map_info.max_entries != 1)
+			continue;
+		if (!map_info.btf_value_type_id)
+			continue;
+		if (!strstr(map_info.name, ".metadata"))
+			continue;
+
+		ret = map_ids[i];
+		break;
+	}
+
+
+free_map_ids:
+	free(map_ids);
+	return ret;
+}
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index 8c1ac4b42f90..8982ffa7cfd2 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -251,6 +251,7 @@ struct bpf_prog_bind_opts {
 
 LIBBPF_API int bpf_prog_bind_map(int prog_fd, int map_fd,
 				 const struct bpf_prog_bind_opts *opts);
+LIBBPF_API int bpf_prog_find_metadata(int prog_fd);
 #ifdef __cplusplus
 } /* extern "C" */
 #endif
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 529b99c0c2c3..b7a40f543b2b 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -307,4 +307,5 @@ LIBBPF_0.2.0 {
 		perf_buffer__buffer_fd;
 		perf_buffer__epoll_fd;
 		perf_buffer__consume_buffer;
+		bpf_prog_find_metadata;
 } LIBBPF_0.1.0;
-- 
2.28.0.402.g5ffc5be6b7-goog