libbpf: Apply map_set_def_max_entries() for inner_maps on creation

This patch allows to auto create BPF_MAP_TYPE_ARRAY_OF_MAPS and
BPF_MAP_TYPE_HASH_OF_MAPS with values of BPF_MAP_TYPE_PERF_EVENT_ARRAY
by bpf_object__load().

Previous behaviour created a zero filled btf_map_def for inner maps and
tried to use it for a map creation but the linux kernel forbids to create
a BPF_MAP_TYPE_PERF_EVENT_ARRAY map with max_entries=0.

Fixes: 646f02ffdd49 ("libbpf: Add BTF-defined map-in-map support")
Signed-off-by: Andrey Grafin <conquistador@yandex-team.ru>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20240117130619.9403-1-conquistador@yandex-team.ru
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index afd09571c482b7234ea827c739980a6996d9ab7f..b8b00da6290714e51a5ebaa35bde8fe6580a5849 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -70,6 +70,7 @@
 
 static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
 static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
+static int map_set_def_max_entries(struct bpf_map *map);
 
 static const char * const attach_type_name[] = {
        [BPF_CGROUP_INET_INGRESS]       = "cgroup_inet_ingress",
@@ -5172,6 +5173,9 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
 
        if (bpf_map_type__is_map_in_map(def->type)) {
                if (map->inner_map) {
+                       err = map_set_def_max_entries(map->inner_map);
+                       if (err)
+                               return err;
                        err = bpf_object__create_map(obj, map->inner_map, true);
                        if (err) {
                                pr_warn("map '%s': failed to create inner map: %d\n",