From: =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
Date: Sat, 2 Nov 2019 12:09:41 +0100
Subject: libbpf: Add auto-pinning of maps when loading BPF objects
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v5.5-rc1
Git-commit: 57a00f41644f20b11c12a27061d814655f633544
References: bsc#1155518

This adds support to libbpf for setting map pinning information as part of
the BTF map declaration, to get automatic map pinning (and reuse) on load.
The pinning type currently only supports a single PIN_BY_NAME mode, where
each map will be pinned by its name in a path that can be overridden, but
defaults to /sys/fs/bpf.

Since auto-pinning only does something if any maps actually have a
'pinning' BTF attribute set, we default the new option to enabled, on the
assumption that seamless pinning is what most callers want.

When a map has a pin_path set at load time, libbpf will compare the map
pinned at that location (if any), and if the attributes match, will re-use
that map instead of creating a new one. If no existing map is found, the
newly created map will instead be pinned at the location.

Programs wanting to customise the pinning can override the pinning paths
using bpf_map__set_pin_path() before calling bpf_object__load() (including
setting it to NULL to disable pinning of a particular map).

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/157269298092.394725.3966306029218559681.stgit@toke.dk
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/bpf_helpers.h |    6 +
 tools/lib/bpf/libbpf.c      |  146 +++++++++++++++++++++++++++++++++++++++++---
 tools/lib/bpf/libbpf.h      |   13 +++
 3 files changed, 156 insertions(+), 9 deletions(-)

--- a/tools/lib/bpf/bpf_helpers.h
+++ b/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
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1093,10 +1093,32 @@ static bool get_map_field_int(const char
 	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;
@@ -1272,6 +1294,30 @@ static int bpf_object__init_user_btf_map
 			}
 			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_warning("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_warning("map '%s': couldn't build pin path.\n",
+						   map_name);
+					return err;
+				}
+			}
 		} else {
 			if (strict) {
 				pr_warning("map '%s': unknown field '%s'.\n",
@@ -1291,7 +1337,8 @@ static int bpf_object__init_user_btf_map
 	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;
@@ -1333,7 +1380,7 @@ static int bpf_object__init_user_btf_map
 	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;
 	}
@@ -1341,7 +1388,8 @@ static int bpf_object__init_user_btf_map
 	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;
@@ -1350,7 +1398,7 @@ static int bpf_object__init_maps(struct
 	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;
 
@@ -1540,7 +1588,8 @@ static int bpf_object__sanitize_and_load
 	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;
@@ -1675,7 +1724,7 @@ static int bpf_object__elf_collect(struc
 	}
 	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)
@@ -2131,6 +2180,66 @@ bpf_object__probe_caps(struct bpf_object
 	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_warning("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_warning("couldn't retrieve pinned map '%s': %s\n",
+			   map->pin_path, cp);
+		return err;
+	}
+
+	if (!map_is_reuse_compat(map, pin_fd)) {
+		pr_warning("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)
 {
@@ -2173,6 +2282,15 @@ bpf_object__create_maps(struct bpf_objec
 		char *cp, errmsg[STRERR_BUFSIZE];
 		int *pfd = &map->fd;
 
+		if (map->pin_path) {
+			err = bpf_object__reuse_map(map);
+			if (err) {
+				pr_warning("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);
@@ -2251,6 +2369,15 @@ err_out:
 			}
 		}
 
+		if (map->pin_path && !map->pinned) {
+			err = bpf_map__pin(map, NULL);
+			if (err) {
+				pr_warning("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);
 	}
 
@@ -3628,6 +3755,7 @@ 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;
@@ -3662,11 +3790,13 @@ __bpf_object__open(const char *path, con
 
 	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);
 
--- a/tools/lib/bpf/libbpf.h
+++ b/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 *
@@ -125,6 +130,12 @@ int bpf_object__section_size(const struc
 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).