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AIO_WRITE(2)		  FreeBSD System Calls Manual		  AIO_WRITE(2)

     aio_write,	aio_writev -- asynchronous write to a file (REALTIME)

     Standard C	Library	(libc, -lc)

     #include <aio.h>

     aio_write(struct aiocb *iocb);

     #include <sys/uio.h>

     aio_writev(struct aiocb *iocb);

     The aio_write() and aio_writev() system calls allow the calling process
     to	write to the descriptor	iocb-_aio_fildes.  aio_write() will write
     iocb-_aio_nbytes from the buffer pointed to by iocb-_aio_buf, whereas
     aio_writev() gathers the data from	the iocb-_aio_iovcnt buffers specified
     by	the members of the iocb-_aio_iov array.	 Both syscalls return immedi-
     ately after the write request has been enqueued to	the descriptor;	the
     write may or may not have completed at the	time the call returns.	If the
     request could not be enqueued, generally due to invalid arguments,	the
     call returns without having enqueued the request.

     For aio_writev() the iovec	structure is defined in	writev(2).

     If	O_APPEND is set	for iocb-_aio_fildes, write operations append to the
     file in the same order as the calls were made.  If	O_APPEND is not	set
     for the file descriptor, the write	operation will occur at	the absolute
     position from the beginning of the	file plus iocb-_aio_offset.

     If	_POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then
     the enqueued operation is submitted at a priority equal to	that of	the
     calling process minus iocb-_aio_reqprio.

     The iocb pointer may be subsequently used as an argument to aio_return()
     and aio_error() in	order to determine return or error status for the en-
     queued operation while it is in progress.

     If	the request is successfully enqueued, the value	of iocb-_aio_offset
     can be modified during the	request	as context, so this value must not be
     referenced	after the request is enqueued.

     The iocb-_aio_sigevent structure can be used to request notification of
     the operation's completion	as described in	aio(4).

     The Asynchronous I/O Control Block	structure pointed to by	iocb and the
     buffer that the iocb-_aio_buf member of that structure references must
     remain valid until	the operation has completed.

     The asynchronous I/O control buffer iocb should be	zeroed before the
     aio_write() or aio_writev() system	call to	avoid passing bogus context
     information to the	kernel.

     Modifications of the Asynchronous I/O Control Block structure or the buf-
     fer contents are not allowed while	the request is queued.

     If	the file offset	in iocb-_aio_offset is past the	offset maximum for
     iocb-_aio_fildes, no I/O will occur.

     The aio_write() and aio_writev() functions	return the value 0 if success-
     ful; otherwise the	value -1 is returned and the global variable errno is
     set to indicate the error.

     The aio_write() and aio_writev() system calls will	fail if:

     [EAGAIN]		The request was	not queued because of system resource

     [EFAULT]		Part of	aio_iov	points outside the process's allocated
			address	space.

     [EINVAL]		The asynchronous notification method in
			iocb-_aio_sigevent.sigev_notify	is invalid or not sup-

     [EOPNOTSUPP]	Asynchronous write operations on the file descriptor
			iocb-_aio_fildes are unsafe and	unsafe asynchronous
			I/O operations are disabled.

     The following conditions may be synchronously detected when the
     aio_write() or aio_writev() system	call is	made, or asynchronously, at
     any time thereafter.  If they are detected	at call	time, aio_write() or
     aio_writev() returns -1 and sets errno appropriately; otherwise the
     aio_return() system call must be called, and will return -1, and
     aio_error() must be called	to determine the actual	value that would have
     been returned in errno.

     [EBADF]		The iocb-_aio_fildes argument is invalid, or is	not
			opened for writing.

     [EINVAL]		The offset iocb-_aio_offset is not valid, the priority
			specified by iocb-_aio_reqprio is not a	valid prior-
			ity, or	the number of bytes specified by
			iocb-_aio_nbytes is not	valid.

     If	the request is successfully enqueued, but subsequently canceled	or an
     error occurs, the value returned by the aio_return() system call is per
     the write(2) system call, and the value returned by the aio_error() sys-
     tem call is either	one of the error returns from the write(2) system
     call, or one of:

     [EBADF]		The iocb-_aio_fildes argument is invalid for writing.

     [ECANCELED]	The request was	explicitly canceled via	a call to

     [EINVAL]		The offset iocb-_aio_offset would be invalid.

     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
     aio_waitcomplete(2), sigevent(3), siginfo(3), aio(4)

     The aio_write() system call is expected to	conform	to the IEEE Std	1003.1
     ("POSIX.1") standard.

     The aio_writev() system call is a FreeBSD extension, and should not be
     used in portable code.

     The aio_write() system call first appeared	in FreeBSD 3.0.	 The
     aio_writev() system call first appeared in	FreeBSD	13.0.

     This manual page was written by Wes Peters	<>.

     Invalid information in iocb-__aiocb_private may confuse the kernel.

FreeBSD	13.0			January	2, 2021			  FreeBSD 13.0


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