errno was of course a mistake once things went threaded. It is not of course supported by system calls, with the error number values either being in the return

errno was of course a mistake once things went threaded. It is not of course supported by system calls, with the error number values either being in the return code, ie return -errno not -1 and that chunk of values is invalid, or returning two values, depending on OS and architecture. Obviously it is going to be really hard to change...