[PATCH bpf-next v3 2/4] libbpf: Store map pin path and status in struct bpf_map

["Toke Høiland-Jørgensen" <toke@redhat.com>]

From: Toke Høiland-Jørgensen <toke@redhat.com>

Support storing and setting a pin path in struct bpf_map, which can be used
for automatic pinning. Also store the pin status so we can avoid attempts
to re-pin a map that has already been pinned (or reused from a previous
pinning).

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 tools/lib/bpf/libbpf.c   |  115 ++++++++++++++++++++++++++++++++++++----------
 tools/lib/bpf/libbpf.h   |    3 +
 tools/lib/bpf/libbpf.map |    3 +
 3 files changed, 97 insertions(+), 24 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ce5ef3ddd263..eb1c5e6ad4a3 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -226,6 +226,8 @@ 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 {
@@ -4025,47 +4027,118 @@ 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->pinned) {
+		pr_warn("map already pinned\n");
+		return -EEXIST;
+	}
+
+	if (path && map->pin_path && strcmp(path, map->pin_path)) {
+		pr_warn("map already has pin path '%s' different from '%s'\n",
+			map->pin_path, path);
+		return -EINVAL;
+	}
+
+	if (!map->pin_path && !path) {
+		pr_warn("missing pin path\n");
+		return -EINVAL;
 	}
 
-	pr_debug("pinned map '%s'\n", path);
+	if (!map->pin_path) {
+		map->pin_path = strdup(path);
+		if (!map->pin_path) {
+			err = -errno;
+			goto out_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;
+	}
+
+	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;
 	}
 
-	err = unlink(path);
+	if (!map->pin_path) {
+		pr_warn("map has no pin_path set\n");
+		return -ENOENT;
+	}
+
+	if (path && strcmp(path, map->pin_path)) {
+		pr_warn("unpin path '%s' differs from map pin path '%s'\n",
+			path, map->pin_path);
+		return -EINVAL;
+	}
+
+	err = check_path(map->pin_path);
+	if (err)
+		return err;
+
+	err = unlink(map->pin_path);
 	if (err != 0)
 		return -errno;
-	pr_debug("unpinned map '%s'\n", path);
+
+	map->pinned = false;
+	pr_debug("unpinned map '%s'\n", map->pin_path);
 
 	return 0;
 }
 
+int bpf_map__set_pin_path(struct bpf_map *map, const char *path)
+{
+	char *old = map->pin_path, *new;
+
+	if (path) {
+		new = strdup(path);
+		if (!new)
+			return -errno;
+	} else {
+		new = NULL;
+	}
+
+	map->pin_path = new;
+	if (old)
+		free(old);
+
+	return 0;
+}
+
+const char *bpf_map__get_pin_path(struct bpf_map *map)
+{
+	return map->pin_path;
+}
+
+bool bpf_map__is_pinned(struct bpf_map *map)
+{
+	return map->pinned;
+}
+
 int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
 {
 	struct bpf_map *map;
@@ -4106,17 +4179,10 @@ 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;
@@ -4266,6 +4332,7 @@ 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);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index c63e2ff84abc..a514729c43f5 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -385,6 +385,9 @@ 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(struct bpf_map *map);
+LIBBPF_API bool bpf_map__is_pinned(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);
 
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index d1473ea4d7a5..c24d4c01591d 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -197,4 +197,7 @@ LIBBPF_0.0.6 {
 		bpf_object__open_mem;
 		bpf_program__get_expected_attach_type;
 		bpf_program__get_type;
+		bpf_map__get_pin_path;
+		bpf_map__set_pin_path;
+		bpf_map__is_pinned;
 } LIBBPF_0.0.5;