If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended.
Function dio_truncate() causes the file referenced by fd to be truncated to at most offset bytes in size. If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended. In the latter case the extended part reads as zero bytes. Returns 0 on success, otherwise -1.