IB/uverbs: Add helper to get array size from ptr attribute

When the parser of an ioctl command has the knowledge that a ptr attribute
in a bundle represents an array of structures, it is useful for it to know
the number of elements in the array. This is done by dividing the
attribute length with the element size.

Signed-off-by: Moni Shoua <monis@mellanox.com>
Reviewed-by: Guy Levi <guyle@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/flow.c

@@ -331,26 +331,24 @@ static int UVERBS_HANDLER(MLX5_IB_METHOD_FLOW_ACTION_CREATE_MODIFY_HEADER)(
 	struct ib_flow_action *action;
 	size_t num_actions;
 	void *in;
-	int len;
 	int ret;
 
 	if (!mlx5_ib_modify_header_supported(mdev))
 		return -EOPNOTSUPP;
 
 	in = uverbs_attr_get_alloced_ptr(attrs,
 		MLX5_IB_ATTR_CREATE_MODIFY_HEADER_ACTIONS_PRM);
-	len = uverbs_attr_get_len(attrs,
-		MLX5_IB_ATTR_CREATE_MODIFY_HEADER_ACTIONS_PRM);
 
-	if (len % MLX5_UN_SZ_BYTES(set_action_in_add_action_in_auto))
-		return -EINVAL;
+	num_actions = uverbs_attr_ptr_get_array_size(
+		attrs, MLX5_IB_ATTR_CREATE_MODIFY_HEADER_ACTIONS_PRM,
+		MLX5_UN_SZ_BYTES(set_action_in_add_action_in_auto));
+	if (num_actions < 0)
+		return num_actions;
 
 	ret = uverbs_get_const(&ft_type, attrs,
 			       MLX5_IB_ATTR_CREATE_MODIFY_HEADER_FT_TYPE);
 	if (ret)
 		return ret;
-
-	num_actions = len / MLX5_UN_SZ_BYTES(set_action_in_add_action_in_auto),
 	action = mlx5_ib_create_modify_header(mdev, ft_type, num_actions, in);
 	if (IS_ERR(action))
 		return PTR_ERR(action);

include/rdma/uverbs_ioctl.h

@@ -719,6 +719,28 @@ uverbs_attr_get_len(const struct uverbs_attr_bundle *attrs_bundle, u16 idx)
 	return attr->ptr_attr.len;
 }
 
+/*
+ * uverbs_attr_ptr_get_array_size() - Get array size pointer by a ptr
+ * attribute.
+ * @attrs: The attribute bundle
+ * @idx: The ID of the attribute
+ * @elem_size: The size of the element in the array
+ */
+static inline int
+uverbs_attr_ptr_get_array_size(struct uverbs_attr_bundle *attrs, u16 idx,
+			       size_t elem_size)
+{
+	int size = uverbs_attr_get_len(attrs, idx);
+
+	if (size < 0)
+		return size;
+
+	if (size % elem_size)
+		return -EINVAL;
+
+	return size / elem_size;
+}
+
 /**
  * uverbs_attr_get_uobjs_arr() - Provides array's properties for attribute for
  * UVERBS_ATTR_TYPE_IDRS_ARRAY.