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