tools lib bpf: Collect map definition in bpf_object

This patch collects more information from maps sections in BPF object
files into 'struct bpf_object', enables later patches access those
information (such as the type and size of the map).

In this patch, a new handler 'struct bpf_map' is extracted in parallel
with bpf_object and bpf_program. Its iterator and accessor is also
created.

Signed-off-by: Wang Nan <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Zefan Li <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/lib/bpf/libbpf.c

···
 	bpf_program_clear_priv_t clear_priv;
 };
 
+struct bpf_map {
+	int fd;
+	struct bpf_map_def def;
+	void *priv;
+	bpf_map_clear_priv_t clear_priv;
+};
+
 static LIST_HEAD(bpf_objects_list);
 
 struct bpf_object {
 	char license[64];
 	u32 kern_version;
-	void *maps_buf;
-	size_t maps_buf_sz;
 
 	struct bpf_program *programs;
 	size_t nr_programs;
-	int *map_fds;
-	/*
-	 * This field is required because maps_buf will be freed and
-	 * maps_buf_sz will be set to 0 after loaded.
-	 */
-	size_t nr_map_fds;
+	struct bpf_map *maps;
+	size_t nr_maps;
+
 	bool loaded;
 
 	/*
···
 bpf_object__init_maps(struct bpf_object *obj, void *data,
 		      size_t size)
 {
-	if (size == 0) {
+	size_t nr_maps;
+	int i;
+
+	nr_maps = size / sizeof(struct bpf_map_def);
+	if (!data || !nr_maps) {
 		pr_debug("%s doesn't need map definition\n",
 			 obj->path);
 		return 0;
 	}
 
-	obj->maps_buf = malloc(size);
-	if (!obj->maps_buf) {
-		pr_warning("malloc maps failed: %s\n", obj->path);
+	pr_debug("maps in %s: %zd bytes\n", obj->path, size);
+
+	obj->maps = calloc(nr_maps, sizeof(obj->maps[0]));
+	if (!obj->maps) {
+		pr_warning("alloc maps for object failed\n");
 		return -ENOMEM;
 	}
+	obj->nr_maps = nr_maps;
 
-	obj->maps_buf_sz = size;
-	memcpy(obj->maps_buf, data, size);
-	pr_debug("maps in %s: %ld bytes\n", obj->path, (long)size);
+	for (i = 0; i < nr_maps; i++) {
+		struct bpf_map_def *def = &obj->maps[i].def;
+
+		/*
+		 * fill all fd with -1 so won't close incorrect
+		 * fd (fd=0 is stdin) when failure (zclose won't close
+		 * negative fd)).
+		 */
+		obj->maps[i].fd = -1;
+
+		/* Save map definition into obj->maps */
+		*def = ((struct bpf_map_def *)data)[i];
+	}
 	return 0;
 }
 
···
 bpf_object__create_maps(struct bpf_object *obj)
 {
 	unsigned int i;
-	size_t nr_maps;
-	int *pfd;
 
-	nr_maps = obj->maps_buf_sz / sizeof(struct bpf_map_def);
-	if (!obj->maps_buf || !nr_maps) {
-		pr_debug("don't need create maps for %s\n",
-			 obj->path);
-		return 0;
-	}
+	for (i = 0; i < obj->nr_maps; i++) {
+		struct bpf_map_def *def = &obj->maps[i].def;
+		int *pfd = &obj->maps[i].fd;
 
-	obj->map_fds = malloc(sizeof(int) * nr_maps);
-	if (!obj->map_fds) {
-		pr_warning("realloc perf_bpf_map_fds failed\n");
-		return -ENOMEM;
-	}
-	obj->nr_map_fds = nr_maps;
-
-	/* fill all fd with -1 */
-	memset(obj->map_fds, -1, sizeof(int) * nr_maps);
-
-	pfd = obj->map_fds;
-	for (i = 0; i < nr_maps; i++) {
-		struct bpf_map_def def;
-
-		def = *(struct bpf_map_def *)(obj->maps_buf +
-				i * sizeof(struct bpf_map_def));
-
-		*pfd = bpf_create_map(def.type,
-				      def.key_size,
-				      def.value_size,
-				      def.max_entries);
+		*pfd = bpf_create_map(def->type,
+				      def->key_size,
+				      def->value_size,
+				      def->max_entries);
 		if (*pfd < 0) {
 			size_t j;
 			int err = *pfd;
···
 			pr_warning("failed to create map: %s\n",
 				   strerror(errno));
 			for (j = 0; j < i; j++)
-				zclose(obj->map_fds[j]);
-			obj->nr_map_fds = 0;
-			zfree(&obj->map_fds);
+				zclose(obj->maps[j].fd);
 			return err;
 		}
 		pr_debug("create map: fd=%d\n", *pfd);
-		pfd++;
 	}
 
-	zfree(&obj->maps_buf);
-	obj->maps_buf_sz = 0;
 	return 0;
 }
 
 static int
-bpf_program__relocate(struct bpf_program *prog, int *map_fds)
+bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
 {
 	int i;
 
···
 			return -LIBBPF_ERRNO__RELOC;
 		}
 		insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
-		insns[insn_idx].imm = map_fds[map_idx];
+		insns[insn_idx].imm = obj->maps[map_idx].fd;
 	}
 
 	zfree(&prog->reloc_desc);
···
 	for (i = 0; i < obj->nr_programs; i++) {
 		prog = &obj->programs[i];
 
-		err = bpf_program__relocate(prog, obj->map_fds);
+		err = bpf_program__relocate(prog, obj);
 		if (err) {
 			pr_warning("failed to relocate '%s'\n",
 				   prog->section_name);
···
 		Elf_Data *data = obj->efile.reloc[i].data;
 		int idx = shdr->sh_info;
 		struct bpf_program *prog;
-		size_t nr_maps = obj->maps_buf_sz /
-				 sizeof(struct bpf_map_def);
+		size_t nr_maps = obj->nr_maps;
 
 		if (shdr->sh_type != SHT_REL) {
 			pr_warning("internal error at %d\n", __LINE__);
···
 	if (!obj)
 		return -EINVAL;
 
-	for (i = 0; i < obj->nr_map_fds; i++)
-		zclose(obj->map_fds[i]);
-	zfree(&obj->map_fds);
-	obj->nr_map_fds = 0;
+	for (i = 0; i < obj->nr_maps; i++)
+		zclose(obj->maps[i].fd);
 
 	for (i = 0; i < obj->nr_programs; i++)
 		bpf_program__unload(&obj->programs[i]);
···
 	bpf_object__elf_finish(obj);
 	bpf_object__unload(obj);
 
-	zfree(&obj->maps_buf);
+	for (i = 0; i < obj->nr_maps; i++) {
+		if (obj->maps[i].clear_priv)
+			obj->maps[i].clear_priv(&obj->maps[i],
+						obj->maps[i].priv);
+		obj->maps[i].priv = NULL;
+		obj->maps[i].clear_priv = NULL;
+	}
+	zfree(&obj->maps);
+	obj->nr_maps = 0;
 
 	if (obj->programs && obj->nr_programs) {
 		for (i = 0; i < obj->nr_programs; i++)
···
 	}
 
 	return fd;
+}
+
+int bpf_map__get_fd(struct bpf_map *map)
+{
+	if (!map)
+		return -EINVAL;
+
+	return map->fd;
+}
+
+int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef)
+{
+	if (!map || !pdef)
+		return -EINVAL;
+
+	*pdef = map->def;
+	return 0;
+}
+
+int bpf_map__set_private(struct bpf_map *map, void *priv,
+			 bpf_map_clear_priv_t clear_priv)
+{
+	if (!map)
+		return -EINVAL;
+
+	if (map->priv) {
+		if (map->clear_priv)
+			map->clear_priv(map, map->priv);
+	}
+
+	map->priv = priv;
+	map->clear_priv = clear_priv;
+	return 0;
+}
+
+int bpf_map__get_private(struct bpf_map *map, void **ppriv)
+{
+	if (!map)
+		return -EINVAL;
+
+	if (ppriv)
+		*ppriv = map->priv;
+	return 0;
+}
+
+struct bpf_map *
+bpf_map__next(struct bpf_map *prev, struct bpf_object *obj)
+{
+	size_t idx;
+	struct bpf_map *s, *e;
+
+	if (!obj || !obj->maps)
+		return NULL;
+
+	s = obj->maps;
+	e = obj->maps + obj->nr_maps;
+
+	if (prev == NULL)
+		return s;
+
+	if ((prev < s) || (prev >= e)) {
+		pr_warning("error in %s: map handler doesn't belong to object\n",
+			   __func__);
+		return NULL;
+	}
+
+	idx = (prev - obj->maps) + 1;
+	if (idx >= obj->nr_maps)
+		return NULL;
+	return &obj->maps[idx];
 }

tools/lib/bpf/libbpf.h

···
 	unsigned int max_entries;
 };
 
+/*
+ * There is another 'struct bpf_map' in include/linux/map.h. However,
+ * it is not a uapi header so no need to consider name clash.
+ */
+struct bpf_map;
+
+struct bpf_map *
+bpf_map__next(struct bpf_map *map, struct bpf_object *obj);
+#define bpf_map__for_each(pos, obj)		\
+	for ((pos) = bpf_map__next(NULL, (obj));	\
+	     (pos) != NULL;				\
+	     (pos) = bpf_map__next((pos), (obj)))
+
+int bpf_map__get_fd(struct bpf_map *map);
+int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef);
+
+typedef void (*bpf_map_clear_priv_t)(struct bpf_map *, void *);
+int bpf_map__set_private(struct bpf_map *map, void *priv,
+			 bpf_map_clear_priv_t clear_priv);
+int bpf_map__get_private(struct bpf_map *map, void **ppriv);
+
 #endif