bpf: Add arraymap support for bpf_for_each_map_elem() helper

This patch added support for arraymap and percpu arraymap.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210226204928.3885192-1-yhs@fb.com

kernel/bpf/arraymap.c

@@ -625,6 +625,42 @@ static const struct bpf_iter_seq_info iter_seq_info = {
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_array_map_info),
 };
 
+static int bpf_for_each_array_elem(struct bpf_map *map, void *callback_fn,
+				   void *callback_ctx, u64 flags)
+{
+	u32 i, key, num_elems = 0;
+	struct bpf_array *array;
+	bool is_percpu;
+	u64 ret = 0;
+	void *val;
+
+	if (flags != 0)
+		return -EINVAL;
+
+	is_percpu = map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY;
+	array = container_of(map, struct bpf_array, map);
+	if (is_percpu)
+		migrate_disable();
+	for (i = 0; i < map->max_entries; i++) {
+		if (is_percpu)
+			val = this_cpu_ptr(array->pptrs[i]);
+		else
+			val = array->value + array->elem_size * i;
+		num_elems++;
+		key = i;
+		ret = BPF_CAST_CALL(callback_fn)((u64)(long)map,
+					(u64)(long)&key, (u64)(long)val,
+					(u64)(long)callback_ctx, 0);
+		/* return value: 0 - continue, 1 - stop and return */
+		if (ret)
+			break;
+	}
+
+	if (is_percpu)
+		migrate_enable();
+	return num_elems;
+}
+
 static int array_map_btf_id;
 const struct bpf_map_ops array_map_ops = {
 	.map_meta_equal = array_map_meta_equal,
@@ -643,6 +679,8 @@ const struct bpf_map_ops array_map_ops = {
 	.map_check_btf = array_map_check_btf,
 	.map_lookup_batch = generic_map_lookup_batch,
 	.map_update_batch = generic_map_update_batch,
+	.map_set_for_each_callback_args = map_set_for_each_callback_args,
+	.map_for_each_callback = bpf_for_each_array_elem,
 	.map_btf_name = "bpf_array",
 	.map_btf_id = &array_map_btf_id,
 	.iter_seq_info = &iter_seq_info,
@@ -660,6 +698,8 @@ const struct bpf_map_ops percpu_array_map_ops = {
 	.map_delete_elem = array_map_delete_elem,
 	.map_seq_show_elem = percpu_array_map_seq_show_elem,
 	.map_check_btf = array_map_check_btf,
+	.map_set_for_each_callback_args = map_set_for_each_callback_args,
+	.map_for_each_callback = bpf_for_each_array_elem,
 	.map_btf_name = "bpf_array",
 	.map_btf_id = &percpu_array_map_btf_id,
 	.iter_seq_info = &iter_seq_info,