AIO_WRITE(3) BSD Library Functions Manual AIO_WRITE(3)
aio_write -- asynchronous write to a file (REALTIME)
POSIX Real-time Library (librt, -lrt)
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
If _POSIX_PRIORITIZED_IO is defined, and the descriptor supports it, then the enqueued oper-
ation is submitted at a priority equal to that of the calling process minus
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
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
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 discour-
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] 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 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, the priority specified by
aiocbp->aio_reqprio is not a valid priority, or the number of bytes spec-
ified 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() 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().
[EINVAL] The offset aiocbp->aio_offset would be invalid.
The aio_write() system call is expected to conform to the IEEE Std 1003.1-2001 (``POSIX.1'')
The aio_write() system call first appeared in NetBSD 5.0.
BSD May 17, 2010 BSD