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

NAME
     aio_write -- asynchronous write to a file (REALTIME)

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <aio.h>

     int
     aio_write(struct aiocb *aiocbp);

DESCRIPTION
     The aio_write() system call allows the calling process to write
     aiocbp->aio_nbytes from the buffer pointed to by aiocbp->aio_buf to the
     descriptor aiocbp->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 aiocbp->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 aiocbp->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 aiocbp->aio_reqprio.

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

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

RESTRICTIONS
     The Asynchronous I/O Control Block structure pointed to by aiocbp and the
     buffer that the aiocbp->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 aiocbp should be zeroed before the
     aio_write() system call to avoid passing bogus context information to the
     kernel.

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

     If the file offset in aiocbp->aio_offset is past the offset maximum  for
     aiocbp->aio_fildes, no I/O will occur.

RETURN VALUES
     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
     error.

ERRORS
     The aio_write() system call will fail if:

     [EAGAIN]           Due to system resource limitations, the request was
                        not queued.

     [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 aiocbp->aio_fildes argument is invalid, or is not
                        opened for writing.

     [EINVAL]           The offset aiocbp->aio_offset is not valid.

     [EINVAL]           The priority specified by aiocbp->aio_reqprio is not a
                        valid priority.

     [EINVAL]           The number of bytes specified by aiocbp->aio_nbytes is
                        not valid.

     [EINVAL]           The constant in aiocbp->aio_sigevent.sigev_notify is
                        set to SIGEV_THREAD (SIGEV_THREAD is not supported).

     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 aiocbp->aio_fildes argument is invalid for writ-
                        ing.

     [ECANCELED]        The request was explicitly canceled via a call to
                        aio_cancel().

SEE ALSO
     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), aio(4)

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

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

AUTHORS
     This manual page was written by Wes Peters <wes@softweyr.com>.

BUGS
     Invalid information in aiocbp->_aiocb_private may confuse the kernel.

BSD                           September 18, 2008                           BSD