NAME
aio_write —
asynchronous write to a file
(REALTIME)
LIBRARY
Standard C Library (libc, -lc)
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 absolute 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] - Due to system resource limitations, the request was not queued.
- [
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 aiocbp->aio_fildes argument is invalid, or is not opened for writing.
- [
EINVAL] - The offset aiocbp->aio_offset is not valid.
- [
EINVAL] - The priority specified by aiocbp->aio_reqprio is not a valid priority.
- [
EINVAL] - The number of bytes specified by aiocbp->aio_nbytes is not valid.
- [
EINVAL] - The constant in aiocbp->aio_sigevent.sigev_notify is set to SIGEV_THREAD (SIGEV_THREAD is not supported).
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().
SEE ALSO
aio_cancel(2), aio_error(2), aio_return(2), aio_suspend(2), 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 aiocbp->_aiocb_private may confuse the kernel.