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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 *aiocbp);

     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 absolute 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.

     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 com-pleted. completed.
     pleted.  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.

     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.

     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 thereafter.  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() system 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 writing.

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

     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), 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 aiocbp->_aiocb_private may confuse the kernel.

BSD                           September 18, 2008                           BSD

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