bpf: Implement bpf iterator for array maps

The bpf iterators for array and percpu array
are implemented. Similar to hash maps, for percpu
array map, bpf program will receive values
from all cpus.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723184115.590532-1-yhs@fb.com

kernel/bpf/arraymap.c

@@ -487,6 +487,142 @@ static int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
 				   vma->vm_pgoff + pgoff);
 }
 
+struct bpf_iter_seq_array_map_info {
+	struct bpf_map *map;
+	void *percpu_value_buf;
+	u32 index;
+};
+
+static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	struct bpf_iter_seq_array_map_info *info = seq->private;
+	struct bpf_map *map = info->map;
+	struct bpf_array *array;
+	u32 index;
+
+	if (info->index >= map->max_entries)
+		return NULL;
+
+	if (*pos == 0)
+		++*pos;
+	array = container_of(map, struct bpf_array, map);
+	index = info->index & array->index_mask;
+	if (info->percpu_value_buf)
+	       return array->pptrs[index];
+	return array->value + array->elem_size * index;
+}
+
+static void *bpf_array_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct bpf_iter_seq_array_map_info *info = seq->private;
+	struct bpf_map *map = info->map;
+	struct bpf_array *array;
+	u32 index;
+
+	++*pos;
+	++info->index;
+	if (info->index >= map->max_entries)
+		return NULL;
+
+	array = container_of(map, struct bpf_array, map);
+	index = info->index & array->index_mask;
+	if (info->percpu_value_buf)
+	       return array->pptrs[index];
+	return array->value + array->elem_size * index;
+}
+
+static int __bpf_array_map_seq_show(struct seq_file *seq, void *v)
+{
+	struct bpf_iter_seq_array_map_info *info = seq->private;
+	struct bpf_iter__bpf_map_elem ctx = {};
+	struct bpf_map *map = info->map;
+	struct bpf_iter_meta meta;
+	struct bpf_prog *prog;
+	int off = 0, cpu = 0;
+	void __percpu **pptr;
+	u32 size;
+
+	meta.seq = seq;
+	prog = bpf_iter_get_info(&meta, v == NULL);
+	if (!prog)
+		return 0;
+
+	ctx.meta = &meta;
+	ctx.map = info->map;
+	if (v) {
+		ctx.key = &info->index;
+
+		if (!info->percpu_value_buf) {
+			ctx.value = v;
+		} else {
+			pptr = v;
+			size = round_up(map->value_size, 8);
+			for_each_possible_cpu(cpu) {
+				bpf_long_memcpy(info->percpu_value_buf + off,
+						per_cpu_ptr(pptr, cpu),
+						size);
+				off += size;
+			}
+			ctx.value = info->percpu_value_buf;
+		}
+	}
+
+	return bpf_iter_run_prog(prog, &ctx);
+}
+
+static int bpf_array_map_seq_show(struct seq_file *seq, void *v)
+{
+	return __bpf_array_map_seq_show(seq, v);
+}
+
+static void bpf_array_map_seq_stop(struct seq_file *seq, void *v)
+{
+	if (!v)
+		(void)__bpf_array_map_seq_show(seq, NULL);
+}
+
+static int bpf_iter_init_array_map(void *priv_data,
+				   struct bpf_iter_aux_info *aux)
+{
+	struct bpf_iter_seq_array_map_info *seq_info = priv_data;
+	struct bpf_map *map = aux->map;
+	void *value_buf;
+	u32 buf_size;
+
+	if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
+		buf_size = round_up(map->value_size, 8) * num_possible_cpus();
+		value_buf = kmalloc(buf_size, GFP_USER | __GFP_NOWARN);
+		if (!value_buf)
+			return -ENOMEM;
+
+		seq_info->percpu_value_buf = value_buf;
+	}
+
+	seq_info->map = map;
+	return 0;
+}
+
+static void bpf_iter_fini_array_map(void *priv_data)
+{
+	struct bpf_iter_seq_array_map_info *seq_info = priv_data;
+
+	kfree(seq_info->percpu_value_buf);
+}
+
+static const struct seq_operations bpf_array_map_seq_ops = {
+	.start	= bpf_array_map_seq_start,
+	.next	= bpf_array_map_seq_next,
+	.stop	= bpf_array_map_seq_stop,
+	.show	= bpf_array_map_seq_show,
+};
+
+static const struct bpf_iter_seq_info iter_seq_info = {
+	.seq_ops		= &bpf_array_map_seq_ops,
+	.init_seq_private	= bpf_iter_init_array_map,
+	.fini_seq_private	= bpf_iter_fini_array_map,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_array_map_info),
+};
+
 static int array_map_btf_id;
 const struct bpf_map_ops array_map_ops = {
 	.map_alloc_check = array_map_alloc_check,
@@ -506,6 +642,7 @@ const struct bpf_map_ops array_map_ops = {
 	.map_update_batch = generic_map_update_batch,
 	.map_btf_name = "bpf_array",
 	.map_btf_id = &array_map_btf_id,
+	.iter_seq_info = &iter_seq_info,
 };
 
 static int percpu_array_map_btf_id;
@@ -521,6 +658,7 @@ const struct bpf_map_ops percpu_array_map_ops = {
 	.map_check_btf = array_map_check_btf,
 	.map_btf_name = "bpf_array",
 	.map_btf_id = &percpu_array_map_btf_id,
+	.iter_seq_info = &iter_seq_info,
 };
 
 static int fd_array_map_alloc_check(union bpf_attr *attr)

kernel/bpf/map_iter.c

@@ -106,10 +106,12 @@ static int bpf_iter_check_map(struct bpf_prog *prog,
 	bool is_percpu = false;
 
 	if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH ||
-	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH)
+	    map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH ||
+	    map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
 		is_percpu = true;
 	else if (map->map_type != BPF_MAP_TYPE_HASH &&
-		 map->map_type != BPF_MAP_TYPE_LRU_HASH)
+		 map->map_type != BPF_MAP_TYPE_LRU_HASH &&
+		 map->map_type != BPF_MAP_TYPE_ARRAY)
 		return -EINVAL;
 
 	key_acc_size = prog->aux->max_rdonly_access;