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.