[PATCH bpf v3] libbpf: Apply map_set_def_max_entries() for inner_maps on creation

[Andrey Grafin <conquistador@xxxxxxxxxxxxxx>]

This patch allows to create BPF_MAP_TYPE_ARRAY_OF_MAPS and
BPF_MAP_TYPE_HASH_OF_MAPS with values of BPF_MAP_TYPE_PERF_EVENT_ARRAY.

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.

Signed-off-by: Andrey Grafin <conquistador@xxxxxxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c                        |  4 +++
 .../selftests/bpf/progs/test_map_in_map.c     | 23 +++++++++++++++
 tools/testing/selftests/bpf/test_maps.c       | 29 ++++++++++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e067be95da3c..8f4d580187aa 100644
--- 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",
@@ -5212,6 +5213,9 @@ 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",
diff --git a/tools/testing/selftests/bpf/progs/test_map_in_map.c b/tools/testing/selftests/bpf/progs/test_map_in_map.c
index f416032ba858..b393d2b8bd6f 100644
--- a/tools/testing/selftests/bpf/progs/test_map_in_map.c
+++ b/tools/testing/selftests/bpf/progs/test_map_in_map.c
@@ -21,6 +21,29 @@ struct {
 	__type(value, __u32);
 } mim_hash SEC(".maps");
 
+struct perf_event_array {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__type(key, __u32);
+	__type(value, __u32);
+} inner_map0 SEC(".maps"), inner_map1 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
+	__uint(max_entries, 2);
+	__type(key, __u32);
+	__array(values, struct perf_event_array);
+} mim_array_pe SEC(".maps") = {
+	.values = {&inner_map0, &inner_map1}};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
+	__uint(max_entries, 2);
+	__type(key, __u32);
+	__array(values, struct perf_event_array);
+} mim_hash_pe SEC(".maps") = {
+	.values = {&inner_map0, &inner_map1}};
+
+
 SEC("xdp")
 int xdp_mimtest0(struct xdp_md *ctx)
 {
diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index 7fc00e423e4d..03f4d448fd3b 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1159,6 +1159,7 @@ static void test_map_in_map(void)
 	__u32 len = sizeof(info);
 	__u32 id = 0;
 	libbpf_print_fn_t old_print_fn;
+	int ret;
 
 	obj = bpf_object__open(MAPINMAP_PROG);
 
@@ -1190,7 +1191,11 @@ static void test_map_in_map(void)
 		goto out_map_in_map;
 	}
 
-	bpf_object__load(obj);
+	ret = bpf_object__load(obj);
+	if (ret) {
+		printf("Failed to load test prog\n");
+		goto out_map_in_map;
+	}
 
 	map = bpf_object__find_map_by_name(obj, "mim_array");
 	if (!map) {
@@ -1226,6 +1231,28 @@ static void test_map_in_map(void)
 		goto out_map_in_map;
 	}
 
+	map = bpf_object__find_map_by_name(obj, "mim_array_pe");
+	if (!map) {
+		printf("Failed to load array of perf event array maps\n");
+		goto out_map_in_map;
+	}
+	mim_fd = bpf_map__fd(map);
+	if (mim_fd < 0) {
+		printf("Failed to get descriptor for array of perf event array maps\n");
+		goto out_map_in_map;
+	}
+
+	map = bpf_object__find_map_by_name(obj, "mim_hash_pe");
+	if (!map) {
+		printf("Failed to load hash of perf event array maps\n");
+		goto out_map_in_map;
+	}
+	mim_fd = bpf_map__fd(map);
+	if (mim_fd < 0) {
+		printf("Failed to get descriptor for array of perf event array maps\n");
+		goto out_map_in_map;
+	}
+
 	close(fd);
 	fd = -1;
 	bpf_object__close(obj);
-- 
2.41.0