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NAME

     aio_write - asynchronous write to a file (REALTIME)

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <aio.h>

     int
     aio_write(struct aiocb *iocb);

DESCRIPTION

     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
     descriptor 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
     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
     enqueued 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.

RESTRICTIONS

     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
     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 iocb->aio_offset is past the offset maximum for
     iocb->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]           The request was not queued because of system resource
                        limitations.

     [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 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
                        priority, 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()
     system 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
                        aio_cancel().

     [EINVAL]           The offset iocb->aio_offset would be invalid.

SEE ALSO

     aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
     aio_waitcomplete(2), siginfo(3), 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 iocb->_aiocb_private may confuse the kernel.