AIO_WRITE(2)              FreeBSD System Calls Manual             AIO_WRITE(2)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <aio.h>

     int
     aio_write(struct aiocb *iocb);

     #include <sys/uio.h>

     int
     aio_writev(struct aiocb *iocb);

DESCRIPTION
     The aio_write() and aio_writev() system calls allow the calling process
     to write to the descriptor iocb->aio_fildes.  aio_write() will write
     iocb->aio_nbytes from the buffer pointed to by iocb->aio_buf, whereas
     aio_writev() gathers the data from the iocb->aio_iovcnt buffers specified
     by the members of the iocb->aio_iov array.  Both syscalls return
     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.

     For aio_writev() the iovec structure is defined in writev(2).

     If O_APPEND is set for iocb->aio_fildes, 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.

     The iocb->aio_sigevent structure can be used to request notification of
     the operation's completion as described in aio(4).

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.

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

     Modifications of the Asynchronous I/O Control Block structure or the
     buffer contents are not allowed while the request is queued.

     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() and aio_writev() functions return 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() and aio_writev() system calls will fail if:

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

     [EFAULT]           Part of aio_iov points outside the process's allocated
                        address space.

     [EINVAL]           The asynchronous notification method in
                        iocb->aio_sigevent.sigev_notify is invalid or not
                        supported.

     [EOPNOTSUPP]       Asynchronous write operations on the file descriptor
                        iocb->aio_fildes are unsafe and unsafe asynchronous
                        I/O operations are disabled.

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

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

     The aio_writev() system call is a FreeBSD extension, and should not be
     used in portable code.

HISTORY
     The aio_write() system call first appeared in FreeBSD 3.0.  The
     aio_writev() system call first appeared in FreeBSD 13.0.

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

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

FreeBSD 13.1-RELEASE-p6         January 2, 2021        FreeBSD 13.1-RELEASE-p6