Ramfile uses sys-file2chan(2), which simplifies implementation but prevents it from knowing when the file has been truncated. Instead, it truncates the file on any write to the start of the file (offset 0), allowing cp(1) to copy in new contents, and text editors to edit it. Indeed, the file will be usable by all applications that do not rely on updating parts of the file in place, or if they do, do not update the start of the file.