The aio_return() function returns the final return status for the asynchronous I/O request with control block pointed to by aiocbp. (See aio(7) for a description of the aiocb structure.)
This function should be called only once for any given request, after aio_error(3) returns something other than EINPROGRESS.
If the asynchronous I/O operation has completed, this function returns the value that would have been returned in case of a synchronous read(2), write(2), fsync(2) or fdatasync(2), call. On error, -1 is returned, and errno is set appropriately.
If the asynchronous I/O operation has not yet completed, the return value and effect of aio_return() are undefined.