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AIO_WRITE(2)		    BSD	System Calls Manual		  AIO_WRITE(2)

     aio_write -- asynchronous write to	a file (REALTIME)

     Standard C	Library	(libc, -lc)

     #include <aio.h>

     aio_write(struct aiocb *iocb);

     The aio_write() system call allows	the calling process to write
     iocb-_aio_nbytes from the buffer pointed to by iocb-_aio_buf to the de-
     scriptor iocb-_aio_fildes.	 The call returns immediately 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.

     If	O_APPEND is set	for iocb-_aio_fildes, aio_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	abso-
     lute 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 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.  For this reason, use of
     auto (stack) variables for	these objects is discouraged.

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

     Modifications of the Asynchronous I/O Control Block structure or the buf-
     fer contents after	the request has	been enqueued, but before the request
     has completed, are	not allowed.

     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() function returns the value	0 if successful; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the

     The aio_write() system call will fail if:

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

     [ENOSYS]		The aio_write()	system call is not supported.

     The following conditions may be synchronously detected when the
     aio_write() system	call is	made, or asynchronously, at any	time there-
     after.  If	they are detected at call time,	aio_write() 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), siginfo(3), aio(4)

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

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

     This manual page was written by Wes Peters	<>.

     Invalid information in iocb-__aiocb_private may confuse the kernel.

BSD				 June 2, 1999				   BSD


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