aio_write(3) - NetBSD Manual Pages

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AIO_WRITE(3)            NetBSD Library Functions Manual           AIO_WRITE(3)


NAME

     aio_write -- asynchronous write to a file (REALTIME)


LIBRARY

     POSIX Real-time Library (librt, -lrt)


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

     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, the prior-
                        ity specified by aiocbp->aio_reqprio is not a valid
                        priority, or the number of bytes specified by
                        aiocbp->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() 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().

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


SEE ALSO

     siginfo(2), aio(3)


STANDARDS

     The aio_write() system call is expected to conform to the IEEE Std
     1003.1-2001 (``POSIX.1'') standard.


HISTORY

     The aio_write() system call first appeared in NetBSD 5.0.

NetBSD 6.0.4                     May 17, 2010                     NetBSD 6.0.4