Merge branch 'map-pinning'

Toke Høiland-Jørgensen says:

====================
This series adds support to libbpf for reading 'pinning' settings from BTF-based
map definitions. It introduces a new open option which can set the pinning path;
if no path is set, /sys/fs/bpf is used as the default. Callers can customise the
pinning between open and load by setting the pin path per map, and still get the
automatic reuse feature.

The semantics of the pinning is similar to the iproute2 "PIN_GLOBAL" setting,
and the eventual goal is to move the iproute2 implementation to be based on
libbpf and the functions introduced in this series.

Changelog:

v6:
  - Fix leak of struct bpf_object in selftest
  - Make struct bpf_map arg const in bpf_map__is_pinned() and bpf_map__get_pin_path()

v5:
  - Don't pin maps with pinning set, but with a value of LIBBPF_PIN_NONE
  - Add a few more selftests:
    - Should not pin map with pinning set, but value LIBBPF_PIN_NONE
    - Should fail to load a map with an invalid pinning value
    - Should fail to re-use maps with parameter mismatch
  - Alphabetise libbpf.map
  - Whitespace and typo fixes

v4:
  - Don't check key_type_id and value_type_id when checking for map reuse
    compatibility.
  - Move building of map->pin_path into init_user_btf_map()
  - Get rid of 'pinning' attribute in struct bpf_map
  - Make sure we also create parent directory on auto-pin (new patch 3).
  - Abort the selftest on error instead of attempting to continue.
  - Support unpinning all pinned maps with bpf_object__unpin_maps(obj, NULL)
  - Support pinning at map->pin_path with bpf_object__pin_maps(obj, NULL)
  - Make re-pinning a map at the same path a noop
  - Rename the open option to pin_root_path
  - Add a bunch more self-tests for pin_maps(NULL) and unpin_maps(NULL)
  - Fix a couple of smaller nits

v3:
  - Drop bpf_object__pin_maps_opts() and just use an open option to customise
    the pin path; also don't touch bpf_object__{un,}pin_maps()
  - Integrate pinning and reuse into bpf_object__create_maps() instead of having
    multiple loops though the map structure
  - Make errors in map reuse and pinning fatal to the load procedure
  - Add selftest to exercise pinning feature
  - Rebase series to latest bpf-next

v2:
  - Drop patch that adds mounting of bpffs
  - Only support a single value of the pinning attribute
  - Add patch to fixup error handling in reuse_fd()
  - Implement the full automatic pinning and map reuse logic on load
====================
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/bpf_helpers.h

@@ -38,4 +38,10 @@ struct bpf_map_def {
 	unsigned int map_flags;
 };
 
+enum libbpf_pin_type {
+	LIBBPF_PIN_NONE,
+	/* PIN_BY_NAME: pin maps by name (in /sys/fs/bpf by default) */
+	LIBBPF_PIN_BY_NAME,
+};
+
 #endif

tools/lib/bpf/libbpf.c

@@ -227,6 +227,8 @@ struct bpf_map {
 	void *priv;
 	bpf_map_clear_priv_t clear_priv;
 	enum libbpf_map_type libbpf_type;
+	char *pin_path;
+	bool pinned;
 };
 
 struct bpf_secdata {
@@ -1091,10 +1093,32 @@ static bool get_map_field_int(const char *map_name, const struct btf *btf,
 	return true;
 }
 
+static int build_map_pin_path(struct bpf_map *map, const char *path)
+{
+	char buf[PATH_MAX];
+	int err, len;
+
+	if (!path)
+		path = "/sys/fs/bpf";
+
+	len = snprintf(buf, PATH_MAX, "%s/%s", path, bpf_map__name(map));
+	if (len < 0)
+		return -EINVAL;
+	else if (len >= PATH_MAX)
+		return -ENAMETOOLONG;
+
+	err = bpf_map__set_pin_path(map, buf);
+	if (err)
+		return err;
+
+	return 0;
+}
+
 static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 					 const struct btf_type *sec,
 					 int var_idx, int sec_idx,
-					 const Elf_Data *data, bool strict)
+					 const Elf_Data *data, bool strict,
+					 const char *pin_root_path)
 {
 	const struct btf_type *var, *def, *t;
 	const struct btf_var_secinfo *vi;
@@ -1269,6 +1293,30 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 			}
 			map->def.value_size = sz;
 			map->btf_value_type_id = t->type;
+		} else if (strcmp(name, "pinning") == 0) {
+			__u32 val;
+			int err;
+
+			if (!get_map_field_int(map_name, obj->btf, def, m,
+					       &val))
+				return -EINVAL;
+			pr_debug("map '%s': found pinning = %u.\n",
+				 map_name, val);
+
+			if (val != LIBBPF_PIN_NONE &&
+			    val != LIBBPF_PIN_BY_NAME) {
+				pr_warn("map '%s': invalid pinning value %u.\n",
+					map_name, val);
+				return -EINVAL;
+			}
+			if (val == LIBBPF_PIN_BY_NAME) {
+				err = build_map_pin_path(map, pin_root_path);
+				if (err) {
+					pr_warn("map '%s': couldn't build pin path.\n",
+						map_name);
+					return err;
+				}
+			}
 		} else {
 			if (strict) {
 				pr_warn("map '%s': unknown field '%s'.\n",
@@ -1288,7 +1336,8 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
 	return 0;
 }
 
-static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict)
+static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
+					  const char *pin_root_path)
 {
 	const struct btf_type *sec = NULL;
 	int nr_types, i, vlen, err;
@@ -1330,7 +1379,7 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict)
 	for (i = 0; i < vlen; i++) {
 		err = bpf_object__init_user_btf_map(obj, sec, i,
 						    obj->efile.btf_maps_shndx,
-						    data, strict);
+						    data, strict, pin_root_path);
 		if (err)
 			return err;
 	}
@@ -1338,7 +1387,8 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict)
 	return 0;
 }
 
-static int bpf_object__init_maps(struct bpf_object *obj, bool relaxed_maps)
+static int bpf_object__init_maps(struct bpf_object *obj, bool relaxed_maps,
+				 const char *pin_root_path)
 {
 	bool strict = !relaxed_maps;
 	int err;
@@ -1347,7 +1397,7 @@ static int bpf_object__init_maps(struct bpf_object *obj, bool relaxed_maps)
 	if (err)
 		return err;
 
-	err = bpf_object__init_user_btf_maps(obj, strict);
+	err = bpf_object__init_user_btf_maps(obj, strict, pin_root_path);
 	if (err)
 		return err;
 
@@ -1536,7 +1586,8 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
 	return 0;
 }
 
-static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps)
+static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps,
+				   const char *pin_root_path)
 {
 	Elf *elf = obj->efile.elf;
 	GElf_Ehdr *ep = &obj->efile.ehdr;
@@ -1671,7 +1722,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps)
 	}
 	err = bpf_object__init_btf(obj, btf_data, btf_ext_data);
 	if (!err)
-		err = bpf_object__init_maps(obj, relaxed_maps);
+		err = bpf_object__init_maps(obj, relaxed_maps, pin_root_path);
 	if (!err)
 		err = bpf_object__sanitize_and_load_btf(obj);
 	if (!err)
@@ -1917,16 +1968,22 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 		return -errno;
 
 	new_fd = open("/", O_RDONLY | O_CLOEXEC);
-	if (new_fd < 0)
+	if (new_fd < 0) {
+		err = -errno;
 		goto err_free_new_name;
+	}
 
 	new_fd = dup3(fd, new_fd, O_CLOEXEC);
-	if (new_fd < 0)
+	if (new_fd < 0) {
+		err = -errno;
 		goto err_close_new_fd;
+	}
 
 	err = zclose(map->fd);
-	if (err)
+	if (err) {
+		err = -errno;
 		goto err_close_new_fd;
+	}
 	free(map->name);
 
 	map->fd = new_fd;
@@ -1945,7 +2002,7 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 	close(new_fd);
 err_free_new_name:
 	free(new_name);
-	return -errno;
+	return err;
 }
 
 int bpf_map__resize(struct bpf_map *map, __u32 max_entries)
@@ -2121,6 +2178,66 @@ bpf_object__probe_caps(struct bpf_object *obj)
 	return 0;
 }
 
+static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
+{
+	struct bpf_map_info map_info = {};
+	char msg[STRERR_BUFSIZE];
+	__u32 map_info_len;
+
+	map_info_len = sizeof(map_info);
+
+	if (bpf_obj_get_info_by_fd(map_fd, &map_info, &map_info_len)) {
+		pr_warn("failed to get map info for map FD %d: %s\n",
+			map_fd, libbpf_strerror_r(errno, msg, sizeof(msg)));
+		return false;
+	}
+
+	return (map_info.type == map->def.type &&
+		map_info.key_size == map->def.key_size &&
+		map_info.value_size == map->def.value_size &&
+		map_info.max_entries == map->def.max_entries &&
+		map_info.map_flags == map->def.map_flags);
+}
+
+static int
+bpf_object__reuse_map(struct bpf_map *map)
+{
+	char *cp, errmsg[STRERR_BUFSIZE];
+	int err, pin_fd;
+
+	pin_fd = bpf_obj_get(map->pin_path);
+	if (pin_fd < 0) {
+		err = -errno;
+		if (err == -ENOENT) {
+			pr_debug("found no pinned map to reuse at '%s'\n",
+				 map->pin_path);
+			return 0;
+		}
+
+		cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
+		pr_warn("couldn't retrieve pinned map '%s': %s\n",
+			map->pin_path, cp);
+		return err;
+	}
+
+	if (!map_is_reuse_compat(map, pin_fd)) {
+		pr_warn("couldn't reuse pinned map at '%s': parameter mismatch\n",
+			map->pin_path);
+		close(pin_fd);
+		return -EINVAL;
+	}
+
+	err = bpf_map__reuse_fd(map, pin_fd);
+	if (err) {
+		close(pin_fd);
+		return err;
+	}
+	map->pinned = true;
+	pr_debug("reused pinned map at '%s'\n", map->pin_path);
+
+	return 0;
+}
+
 static int
 bpf_object__populate_internal_map(struct bpf_object *obj, struct bpf_map *map)
 {
@@ -2163,6 +2280,15 @@ bpf_object__create_maps(struct bpf_object *obj)
 		char *cp, errmsg[STRERR_BUFSIZE];
 		int *pfd = &map->fd;
 
+		if (map->pin_path) {
+			err = bpf_object__reuse_map(map);
+			if (err) {
+				pr_warn("error reusing pinned map %s\n",
+					map->name);
+				return err;
+			}
+		}
+
 		if (map->fd >= 0) {
 			pr_debug("skip map create (preset) %s: fd=%d\n",
 				 map->name, map->fd);
@@ -2241,6 +2367,15 @@ bpf_object__create_maps(struct bpf_object *obj)
 			}
 		}
 
+		if (map->pin_path && !map->pinned) {
+			err = bpf_map__pin(map, NULL);
+			if (err) {
+				pr_warn("failed to auto-pin map name '%s' at '%s'\n",
+					map->name, map->pin_path);
+				return err;
+			}
+		}
+
 		pr_debug("created map %s: fd=%d\n", map->name, *pfd);
 	}
 
@@ -3615,6 +3750,7 @@ static struct bpf_object *
 __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 		   struct bpf_object_open_opts *opts)
 {
+	const char *pin_root_path;
 	struct bpf_program *prog;
 	struct bpf_object *obj;
 	const char *obj_name;
@@ -3649,11 +3785,13 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 
 	obj->relaxed_core_relocs = OPTS_GET(opts, relaxed_core_relocs, false);
 	relaxed_maps = OPTS_GET(opts, relaxed_maps, false);
+	pin_root_path = OPTS_GET(opts, pin_root_path, NULL);
 
 	CHECK_ERR(bpf_object__elf_init(obj), err, out);
 	CHECK_ERR(bpf_object__check_endianness(obj), err, out);
 	CHECK_ERR(bpf_object__probe_caps(obj), err, out);
-	CHECK_ERR(bpf_object__elf_collect(obj, relaxed_maps), err, out);
+	CHECK_ERR(bpf_object__elf_collect(obj, relaxed_maps, pin_root_path),
+		  err, out);
 	CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
 	bpf_object__elf_finish(obj);
 
@@ -3808,6 +3946,28 @@ int bpf_object__load(struct bpf_object *obj)
 	return bpf_object__load_xattr(&attr);
 }
 
+static int make_parent_dir(const char *path)
+{
+	char *cp, errmsg[STRERR_BUFSIZE];
+	char *dname, *dir;
+	int err = 0;
+
+	dname = strdup(path);
+	if (dname == NULL)
+		return -ENOMEM;
+
+	dir = dirname(dname);
+	if (mkdir(dir, 0700) && errno != EEXIST)
+		err = -errno;
+
+	free(dname);
+	if (err) {
+		cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
+		pr_warn("failed to mkdir %s: %s\n", path, cp);
+	}
+	return err;
+}
+
 static int check_path(const char *path)
 {
 	char *cp, errmsg[STRERR_BUFSIZE];
@@ -3844,6 +4004,10 @@ int bpf_program__pin_instance(struct bpf_program *prog, const char *path,
 	char *cp, errmsg[STRERR_BUFSIZE];
 	int err;
 
+	err = make_parent_dir(path);
+	if (err)
+		return err;
+
 	err = check_path(path);
 	if (err)
 		return err;
@@ -3897,25 +4061,14 @@ int bpf_program__unpin_instance(struct bpf_program *prog, const char *path,
 	return 0;
 }
 
-static int make_dir(const char *path)
-{
-	char *cp, errmsg[STRERR_BUFSIZE];
-	int err = 0;
-
-	if (mkdir(path, 0700) && errno != EEXIST)
-		err = -errno;
-
-	if (err) {
-		cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
-		pr_warn("failed to mkdir %s: %s\n", path, cp);
-	}
-	return err;
-}
-
 int bpf_program__pin(struct bpf_program *prog, const char *path)
 {
 	int i, err;
 
+	err = make_parent_dir(path);
+	if (err)
+		return err;
+
 	err = check_path(path);
 	if (err)
 		return err;
@@ -3936,10 +4089,6 @@ int bpf_program__pin(struct bpf_program *prog, const char *path)
 		return bpf_program__pin_instance(prog, path, 0);
 	}
 
-	err = make_dir(path);
-	if (err)
-		return err;
-
 	for (i = 0; i < prog->instances.nr; i++) {
 		char buf[PATH_MAX];
 		int len;
@@ -4030,47 +4179,123 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
 	char *cp, errmsg[STRERR_BUFSIZE];
 	int err;
 
-	err = check_path(path);
-	if (err)
-		return err;
-
 	if (map == NULL) {
 		pr_warn("invalid map pointer\n");
 		return -EINVAL;
 	}
 
-	if (bpf_obj_pin(map->fd, path)) {
-		cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
-		pr_warn("failed to pin map: %s\n", cp);
-		return -errno;
+	if (map->pin_path) {
+		if (path && strcmp(path, map->pin_path)) {
+			pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
+				bpf_map__name(map), map->pin_path, path);
+			return -EINVAL;
+		} else if (map->pinned) {
+			pr_debug("map '%s' already pinned at '%s'; not re-pinning\n",
+				 bpf_map__name(map), map->pin_path);
+			return 0;
+		}
+	} else {
+		if (!path) {
+			pr_warn("missing a path to pin map '%s' at\n",
+				bpf_map__name(map));
+			return -EINVAL;
+		} else if (map->pinned) {
+			pr_warn("map '%s' already pinned\n", bpf_map__name(map));
+			return -EEXIST;
+		}
+
+		map->pin_path = strdup(path);
+		if (!map->pin_path) {
+			err = -errno;
+			goto out_err;
+		}
+	}
+
+	err = make_parent_dir(map->pin_path);
+	if (err)
+		return err;
+
+	err = check_path(map->pin_path);
+	if (err)
+		return err;
+
+	if (bpf_obj_pin(map->fd, map->pin_path)) {
+		err = -errno;
+		goto out_err;
 	}
 
-	pr_debug("pinned map '%s'\n", path);
+	map->pinned = true;
+	pr_debug("pinned map '%s'\n", map->pin_path);
 
 	return 0;
+
+out_err:
+	cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
+	pr_warn("failed to pin map: %s\n", cp);
+	return err;
 }
 
 int bpf_map__unpin(struct bpf_map *map, const char *path)
 {
 	int err;
 
-	err = check_path(path);
-	if (err)
-		return err;
-
 	if (map == NULL) {
 		pr_warn("invalid map pointer\n");
 		return -EINVAL;
 	}
 
+	if (map->pin_path) {
+		if (path && strcmp(path, map->pin_path)) {
+			pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
+				bpf_map__name(map), map->pin_path, path);
+			return -EINVAL;
+		}
+		path = map->pin_path;
+	} else if (!path) {
+		pr_warn("no path to unpin map '%s' from\n",
+			bpf_map__name(map));
+		return -EINVAL;
+	}
+
+	err = check_path(path);
+	if (err)
+		return err;
+
 	err = unlink(path);
 	if (err != 0)
 		return -errno;
-	pr_debug("unpinned map '%s'\n", path);
+
+	map->pinned = false;
+	pr_debug("unpinned map '%s' from '%s'\n", bpf_map__name(map), path);
 
 	return 0;
 }
 
+int bpf_map__set_pin_path(struct bpf_map *map, const char *path)
+{
+	char *new = NULL;
+
+	if (path) {
+		new = strdup(path);
+		if (!new)
+			return -errno;
+	}
+
+	free(map->pin_path);
+	map->pin_path = new;
+	return 0;
+}
+
+const char *bpf_map__get_pin_path(const struct bpf_map *map)
+{
+	return map->pin_path;
+}
+
+bool bpf_map__is_pinned(const struct bpf_map *map)
+{
+	return map->pinned;
+}
+
 int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 {
 	struct bpf_map *map;
@@ -4084,25 +4309,28 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 		return -ENOENT;
 	}
 
-	err = make_dir(path);
-	if (err)
-		return err;
-
 	bpf_object__for_each_map(map, obj) {
+		char *pin_path = NULL;
 		char buf[PATH_MAX];
-		int len;
 
-		len = snprintf(buf, PATH_MAX, "%s/%s", path,
-			       bpf_map__name(map));
-		if (len < 0) {
-			err = -EINVAL;
-			goto err_unpin_maps;
-		} else if (len >= PATH_MAX) {
-			err = -ENAMETOOLONG;
-			goto err_unpin_maps;
+		if (path) {
+			int len;
+
+			len = snprintf(buf, PATH_MAX, "%s/%s", path,
+				       bpf_map__name(map));
+			if (len < 0) {
+				err = -EINVAL;
+				goto err_unpin_maps;
+			} else if (len >= PATH_MAX) {
+				err = -ENAMETOOLONG;
+				goto err_unpin_maps;
+			}
+			pin_path = buf;
+		} else if (!map->pin_path) {
+			continue;
 		}
 
-		err = bpf_map__pin(map, buf);
+		err = bpf_map__pin(map, pin_path);
 		if (err)
 			goto err_unpin_maps;
 	}
@@ -4111,17 +4339,10 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 
 err_unpin_maps:
 	while ((map = bpf_map__prev(map, obj))) {
-		char buf[PATH_MAX];
-		int len;
-
-		len = snprintf(buf, PATH_MAX, "%s/%s", path,
-			       bpf_map__name(map));
-		if (len < 0)
-			continue;
-		else if (len >= PATH_MAX)
+		if (!map->pin_path)
 			continue;
 
-		bpf_map__unpin(map, buf);
+		bpf_map__unpin(map, NULL);
 	}
 
 	return err;
@@ -4136,17 +4357,24 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
 		return -ENOENT;
 
 	bpf_object__for_each_map(map, obj) {
+		char *pin_path = NULL;
 		char buf[PATH_MAX];
-		int len;
 
-		len = snprintf(buf, PATH_MAX, "%s/%s", path,
-			       bpf_map__name(map));
-		if (len < 0)
-			return -EINVAL;
-		else if (len >= PATH_MAX)
-			return -ENAMETOOLONG;
+		if (path) {
+			int len;
+
+			len = snprintf(buf, PATH_MAX, "%s/%s", path,
+				       bpf_map__name(map));
+			if (len < 0)
+				return -EINVAL;
+			else if (len >= PATH_MAX)
+				return -ENAMETOOLONG;
+			pin_path = buf;
+		} else if (!map->pin_path) {
+			continue;
+		}
 
-		err = bpf_map__unpin(map, buf);
+		err = bpf_map__unpin(map, pin_path);
 		if (err)
 			return err;
 	}
@@ -4167,10 +4395,6 @@ int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
 		return -ENOENT;
 	}
 
-	err = make_dir(path);
-	if (err)
-		return err;
-
 	bpf_object__for_each_program(prog, obj) {
 		char buf[PATH_MAX];
 		int len;
@@ -4271,6 +4495,7 @@ void bpf_object__close(struct bpf_object *obj)
 
 	for (i = 0; i < obj->nr_maps; i++) {
 		zfree(&obj->maps[i].name);
+		zfree(&obj->maps[i].pin_path);
 		if (obj->maps[i].clear_priv)
 			obj->maps[i].clear_priv(&obj->maps[i],
 						obj->maps[i].priv);

tools/lib/bpf/libbpf.h

@@ -103,8 +103,13 @@ struct bpf_object_open_opts {
 	bool relaxed_maps;
 	/* process CO-RE relocations non-strictly, allowing them to fail */
 	bool relaxed_core_relocs;
+	/* maps that set the 'pinning' attribute in their definition will have
+	 * their pin_path attribute set to a file in this directory, and be
+	 * auto-pinned to that path on load; defaults to "/sys/fs/bpf".
+	 */
+	const char *pin_root_path;
 };
-#define bpf_object_open_opts__last_field relaxed_core_relocs
+#define bpf_object_open_opts__last_field pin_root_path
 
 LIBBPF_API struct bpf_object *bpf_object__open(const char *path);
 LIBBPF_API struct bpf_object *
@@ -124,6 +129,17 @@ int bpf_object__section_size(const struct bpf_object *obj, const char *name,
 			     __u32 *size);
 int bpf_object__variable_offset(const struct bpf_object *obj, const char *name,
 				__u32 *off);
+
+enum libbpf_pin_type {
+	LIBBPF_PIN_NONE,
+	/* PIN_BY_NAME: pin maps by name (in /sys/fs/bpf by default) */
+	LIBBPF_PIN_BY_NAME,
+};
+
+/* pin_maps and unpin_maps can both be called with a NULL path, in which case
+ * they will use the pin_path attribute of each map (and ignore all maps that
+ * don't have a pin_path set).
+ */
 LIBBPF_API int bpf_object__pin_maps(struct bpf_object *obj, const char *path);
 LIBBPF_API int bpf_object__unpin_maps(struct bpf_object *obj,
 				      const char *path);
@@ -387,6 +403,9 @@ LIBBPF_API int bpf_map__resize(struct bpf_map *map, __u32 max_entries);
 LIBBPF_API bool bpf_map__is_offload_neutral(const struct bpf_map *map);
 LIBBPF_API bool bpf_map__is_internal(const struct bpf_map *map);
 LIBBPF_API void bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex);
+LIBBPF_API int bpf_map__set_pin_path(struct bpf_map *map, const char *path);
+LIBBPF_API const char *bpf_map__get_pin_path(const struct bpf_map *map);
+LIBBPF_API bool bpf_map__is_pinned(const struct bpf_map *map);
 LIBBPF_API int bpf_map__pin(struct bpf_map *map, const char *path);
 LIBBPF_API int bpf_map__unpin(struct bpf_map *map, const char *path);
 

tools/lib/bpf/libbpf.map

@@ -193,6 +193,9 @@ LIBBPF_0.0.5 {
 
 LIBBPF_0.0.6 {
 	global:
+		bpf_map__get_pin_path;
+		bpf_map__is_pinned;
+		bpf_map__set_pin_path;
 		bpf_object__open_file;
 		bpf_object__open_mem;
 		bpf_program__get_expected_attach_type;

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

+// SPDX-License-Identifier: GPL-2.0
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <test_progs.h>
+
+__u32 get_map_id(struct bpf_object *obj, const char *name)
+{
+	struct bpf_map_info map_info = {};
+	__u32 map_info_len, duration = 0;
+	struct bpf_map *map;
+	int err;
+
+	map_info_len = sizeof(map_info);
+
+	map = bpf_object__find_map_by_name(obj, name);
+	if (CHECK(!map, "find map", "NULL map"))
+		return 0;
+
+	err = bpf_obj_get_info_by_fd(bpf_map__fd(map),
+				     &map_info, &map_info_len);
+	CHECK(err, "get map info", "err %d errno %d", err, errno);
+	return map_info.id;
+}
+
+void test_pinning(void)
+{
+	const char *file_invalid = "./test_pinning_invalid.o";
+	const char *custpinpath = "/sys/fs/bpf/custom/pinmap";
+	const char *nopinpath = "/sys/fs/bpf/nopinmap";
+	const char *nopinpath2 = "/sys/fs/bpf/nopinmap2";
+	const char *custpath = "/sys/fs/bpf/custom";
+	const char *pinpath = "/sys/fs/bpf/pinmap";
+	const char *file = "./test_pinning.o";
+	__u32 map_id, map_id2, duration = 0;
+	struct stat statbuf = {};
+	struct bpf_object *obj;
+	struct bpf_map *map;
+	int err;
+	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
+		.pin_root_path = custpath,
+	);
+
+	/* check that opening fails with invalid pinning value in map def */
+	obj = bpf_object__open_file(file_invalid, NULL);
+	err = libbpf_get_error(obj);
+	if (CHECK(err != -EINVAL, "invalid open", "err %d errno %d\n", err, errno)) {
+		obj = NULL;
+		goto out;
+	}
+
+	/* open the valid object file  */
+	obj = bpf_object__open_file(file, NULL);
+	err = libbpf_get_error(obj);
+	if (CHECK(err, "default open", "err %d errno %d\n", err, errno)) {
+		obj = NULL;
+		goto out;
+	}
+
+	err = bpf_object__load(obj);
+	if (CHECK(err, "default load", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that pinmap was pinned */
+	err = stat(pinpath, &statbuf);
+	if (CHECK(err, "stat pinpath", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that nopinmap was *not* pinned */
+	err = stat(nopinpath, &statbuf);
+	if (CHECK(!err || errno != ENOENT, "stat nopinpath",
+		  "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that nopinmap2 was *not* pinned */
+	err = stat(nopinpath2, &statbuf);
+	if (CHECK(!err || errno != ENOENT, "stat nopinpath2",
+		  "err %d errno %d\n", err, errno))
+		goto out;
+
+	map_id = get_map_id(obj, "pinmap");
+	if (!map_id)
+		goto out;
+
+	bpf_object__close(obj);
+
+	obj = bpf_object__open_file(file, NULL);
+	if (CHECK_FAIL(libbpf_get_error(obj))) {
+		obj = NULL;
+		goto out;
+	}
+
+	err = bpf_object__load(obj);
+	if (CHECK(err, "default load", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that same map ID was reused for second load */
+	map_id2 = get_map_id(obj, "pinmap");
+	if (CHECK(map_id != map_id2, "check reuse",
+		  "err %d errno %d id %d id2 %d\n", err, errno, map_id, map_id2))
+		goto out;
+
+	/* should be no-op to re-pin same map */
+	map = bpf_object__find_map_by_name(obj, "pinmap");
+	if (CHECK(!map, "find map", "NULL map"))
+		goto out;
+
+	err = bpf_map__pin(map, NULL);
+	if (CHECK(err, "re-pin map", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* but error to pin at different location */
+	err = bpf_map__pin(map, "/sys/fs/bpf/other");
+	if (CHECK(!err, "pin map different", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* unpin maps with a pin_path set */
+	err = bpf_object__unpin_maps(obj, NULL);
+	if (CHECK(err, "unpin maps", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* and re-pin them... */
+	err = bpf_object__pin_maps(obj, NULL);
+	if (CHECK(err, "pin maps", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* set pinning path of other map and re-pin all */
+	map = bpf_object__find_map_by_name(obj, "nopinmap");
+	if (CHECK(!map, "find map", "NULL map"))
+		goto out;
+
+	err = bpf_map__set_pin_path(map, custpinpath);
+	if (CHECK(err, "set pin path", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* should only pin the one unpinned map */
+	err = bpf_object__pin_maps(obj, NULL);
+	if (CHECK(err, "pin maps", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that nopinmap was pinned at the custom path */
+	err = stat(custpinpath, &statbuf);
+	if (CHECK(err, "stat custpinpath", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* remove the custom pin path to re-test it with auto-pinning below */
+	err = unlink(custpinpath);
+	if (CHECK(err, "unlink custpinpath", "err %d errno %d\n", err, errno))
+		goto out;
+
+	err = rmdir(custpath);
+	if (CHECK(err, "rmdir custpindir", "err %d errno %d\n", err, errno))
+		goto out;
+
+	bpf_object__close(obj);
+
+	/* open the valid object file again */
+	obj = bpf_object__open_file(file, NULL);
+	err = libbpf_get_error(obj);
+	if (CHECK(err, "default open", "err %d errno %d\n", err, errno)) {
+		obj = NULL;
+		goto out;
+	}
+
+	/* swap pin paths of the two maps */
+	bpf_object__for_each_map(map, obj) {
+		if (!strcmp(bpf_map__name(map), "nopinmap"))
+			err = bpf_map__set_pin_path(map, pinpath);
+		else if (!strcmp(bpf_map__name(map), "pinmap"))
+			err = bpf_map__set_pin_path(map, NULL);
+		else
+			continue;
+
+		if (CHECK(err, "set pin path", "err %d errno %d\n", err, errno))
+			goto out;
+	}
+
+	/* should fail because of map parameter mismatch */
+	err = bpf_object__load(obj);
+	if (CHECK(err != -EINVAL, "param mismatch load", "err %d errno %d\n", err, errno))
+		goto out;
+
+	bpf_object__close(obj);
+
+	/* test auto-pinning at custom path with open opt */
+	obj = bpf_object__open_file(file, &opts);
+	if (CHECK_FAIL(libbpf_get_error(obj))) {
+		obj = NULL;
+		goto out;
+	}
+
+	err = bpf_object__load(obj);
+	if (CHECK(err, "custom load", "err %d errno %d\n", err, errno))
+		goto out;
+
+	/* check that pinmap was pinned at the custom path */
+	err = stat(custpinpath, &statbuf);
+	if (CHECK(err, "stat custpinpath", "err %d errno %d\n", err, errno))
+		goto out;
+
+out:
+	unlink(pinpath);
+	unlink(nopinpath);
+	unlink(nopinpath2);
+	unlink(custpinpath);
+	rmdir(custpath);
+	if (obj)
+		bpf_object__close(obj);
+}

tools/testing/selftests/bpf/progs/test_pinning.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+int _version SEC("version") = 1;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(pinning, LIBBPF_PIN_BY_NAME);
+} pinmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+} nopinmap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(pinning, LIBBPF_PIN_NONE);
+} nopinmap2 SEC(".maps");
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/test_pinning_invalid.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+int _version SEC("version") = 1;
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u64);
+	__uint(pinning, 2); /* invalid */
+} nopinmap3 SEC(".maps");
+
+char _license[] SEC("license") = "GPL";