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aio_write — asynchronous write to a file (REALTIME)
Standard C Library (libc, -lc)
aio_write(struct aiocb *iocb);
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.
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
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.
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
The aio_write() system call will fail if:
[EAGAIN] The request was not queued because of system resource
[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
[EINVAL] The offset iocb->aio_offset would be invalid.
aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2),
aio_waitcomplete(2), siginfo(3), aio(4)
The aio_write() system call is expected to conform to the IEEE Std 1003.1
The aio_write() system call first appeared in FreeBSD 3.0.
This manual page was written by Wes Peters ⟨firstname.lastname@example.org⟩.
Invalid information in iocb->_aiocb_private may confuse the kernel.