[PATCH bpf-next] libbpf: Add bpf_map__set_name()

[Joe Burton <jevburton.kernel@gmail.com>]

From: Joe Burton <jevburton@google.com>

Add the capability to set a `struct bpf_map` name.

bpf_map__reuse_fd(struct bpf_map *map, int fd) does the following:

1. get the bpf_map_info of the passed-in fd
2. strdup the name from the bpf_map_info
3. assign that name to the map
4. and some other stuff

While `map.name` may initially be arbitrarily long, this operation
truncates it after 15 characters.

We have some infrastructure that uses bpf_map__reuse_fd() to preserve
maps across upgrades. Some of our users have long map names, and are
seeing their maps 'disappear' after an upgrade, due to the name
truncation.

By invoking `bpf_map__set_name()` after `bpf_map__reuse_fd()`, we can
trivially work around the issue.

Signed-off-by: Joe Burton <jevburton@google.com>
---
 tools/lib/bpf/libbpf.c | 22 ++++++++++++++++++++++
 tools/lib/bpf/libbpf.h |  3 ++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 72548798126b..725baf508e6f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9089,6 +9089,28 @@ const char *bpf_map__name(const struct bpf_map *map)
 	return map->name;
 }
 
+int bpf_map__set_name(struct bpf_map *map, const char *name)
+{
+	char *new_name;
+
+	if (!map)
+		return libbpf_err(-EINVAL);
+
+	new_name = strdup(name);
+	if (!new_name)
+		return libbpf_err(-ENOMEM);
+
+	if (map_uses_real_name(map)) {
+		free(map->real_name);
+		map->real_name = new_name;
+	} else {
+		free(map->name);
+		map->name = new_name;
+	}
+
+	return 0;
+}
+
 enum bpf_map_type bpf_map__type(const struct bpf_map *map)
 {
 	return map->def.type;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index e4d5353f757b..e898c4cb514a 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -731,8 +731,9 @@ LIBBPF_API bool bpf_map__autocreate(const struct bpf_map *map);
  */
 LIBBPF_API int bpf_map__fd(const struct bpf_map *map);
 LIBBPF_API int bpf_map__reuse_fd(struct bpf_map *map, int fd);
-/* get map name */
+/* get/set map name */
 LIBBPF_API const char *bpf_map__name(const struct bpf_map *map);
+LIBBPF_API int bpf_map__set_name(struct bpf_map *map, const char *name);
 /* get/set map type */
 LIBBPF_API enum bpf_map_type bpf_map__type(const struct bpf_map *map);
 LIBBPF_API int bpf_map__set_type(struct bpf_map *map, enum bpf_map_type type);
-- 
2.37.0.144.g8ac04bfd2-goog