The aio_fsync() function does a sync on all outstanding asynchronous I/O operations associated with aiocbp->aio_fildes. (See aio(7) for a description of the aiocb structure.)
More precisely, if op is O_SYNC, then all currently queued I/O operations shall be completed as if by a call of fsync(2), and if op is O_DSYNC, this call is the asynchronous analog of fdatasync(2).
Note that this is a request only; it does not wait for I/O completion.
Apart from aio_fildes, the only field in the structure pointed to by aiocbp that is used by this call is the aio_sigevent field (a sigevent structure, described in sigevent(7)), which indicates the desired type of asynchronous notification at completion. All other fields are ignored.