+ /*
+ * Update ->io_size depending on options specified.
+ * ->file_size_low being 0 means filesize option isn't set.
+ * Non zero ->file_size_low equals ->file_size_high means
+ * filesize option is set in a fixed size format.
+ * Non zero ->file_size_low not equals ->file_size_high means
+ * filesize option is set in a range format.
+ */