aioread, aiowrite - read or write asynchronous I/O operations
int aioread(int fildes, char *bufp, int bufs, off_t offset,
int whence, aio_result_t *resultp);
int aiowrite(int fildes, const char *bufp, int bufs, off_t offset,
int whence, aio_result_t *resultp);
The aioread() function initiates one asynchronous read(2) and returns
control to the calling program. The read continues concurrently with
other activity of the process. An attempt is made to read bufs bytes of
data from the object referenced by the descriptor fildes into the buf‐
fer pointed to by bufp.
The aiowrite() function initiates one asynchronous write(2) and returns
control to the calling program. The write continues concurrently with
other activity of the process. An attempt is made to write bufs bytes
of data from the buffer pointed to by bufp to the object referenced by
the descriptor fildes.
On objects capable of seeking, the I/O operation starts at the position
specified by whence and offset. These parameters have the same meaning
as the corresponding parameters to the llseek(2) function. On objects
not capable of seeking the I/O operation always start from the current
position and the parameters whence and offset are ignored. The seek
pointer for objects capable of seeking is not updated by aioread() or
aiowrite(). Sequential asynchronous operations on these devices must be
managed by the application using the whence and offset parameters.
The result of the asynchronous operation is stored in the structure
pointed to by resultp:
int aio_return; /* return value of read() or write() */
int aio_errno; /* value of errno for read() or write() */
Upon completion of the operation both aio_return and aio_errno are set
to reflect the result of the operation. Since AIO_INPROGRESS is not a
value used by the system, the client can detect a change in state by
initializing aio_return to this value.
The application-supplied buffer bufp should not be referenced by the
application until after the operation has completed. While the opera‐
tion is in progress, this buffer is in use by the operating system.
Notification of the completion of an asynchronous I/O operation can be
obtained synchronously through the aiowait(3C) function, or asyn‐
chronously by installing a signal handler for the SIGIO signal. Asyn‐
chronous notification is accomplished by sending the process a SIGIO
signal. If a signal handler is not installed for the SIGIO signal,
asynchronous notification is disabled. The delivery of this instance of
the SIGIO signal is reliable in that a signal delivered while the han‐
dler is executing is not lost. If the client ensures that aiowait()
returns nothing (using a polling timeout) before returning from the
signal handler, no asynchronous I/O notifications are lost. The
aiowait() function is the only way to dequeue an asynchronous notifica‐
tion. The SIGIO signal can have several meanings simultaneously. For
example, it can signify that a descriptor generated SIGIO and an asyn‐
chronous operation completed. Further, issuing an asynchronous request
successfully guarantees that space exists to queue the completion noti‐
The close(2), exit(2) and execve(2)) functions block until all pending
asynchronous I/O operations can be canceled by the system.
It is an error to use the same result buffer in more than one outstand‐
ing request. These structures can be reused only after the system has
completed the operation.
Upon successful completion, aioread() and aiowrite() return 0. Upon
failure, aioread() and aiowrite() return −1 and set errno to indicate
The aioread() and aiowrite() functions will fail if:
The number of asynchronous requests that the system can han‐
dle at any one time has been exceeded
The fildes argument is not a valid file descriptor open for
At least one of bufp or resultp points to an address outside
the address space of the requesting process. This condition
is reported only if detected by the application process.
The resultp argument is currently being used by an outstand‐
ing asynchronous request.
The offset argument is not a valid offset for this file sys‐
Memory resources are unavailable to initiate request.
The aioread() and aiowrite() functions have transitional interfaces for
64-bit file offsets. See lf64(5).
See attributes(5) for descriptions of the following attributes:
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│MT-Level │ Safe │
SEE ALSOclose(2), execve(2), exit(2), llseek(2), lseek(2), open(2), read(2),
write(2), aiocancel(3C), aiowait(3C), sigvec(3UCB), attributes(5),
Feb 5, 2008 AIOREAD(3C)