NAME
aio_write
,
aio_writev
—
asynchronous write to a file
(REALTIME)
LIBRARY
library “libc”
SYNOPSIS
#include
<aio.h>
int
aio_write
(struct
aiocb *iocb);
#include
<sys/uio.h>
int
aio_writev
(struct
aiocb *iocb);
DESCRIPTION
Theaio_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.