AIOREAD(3C) Standard C Library Functions AIOREAD(3C)


aioread, aiowrite - read or write asynchronous I/O operations


#include <sys/types.h>
#include <sys/asynch.h>

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 buffer
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 operation
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
asynchronously by installing a signal handler for the SIGIO signal.
Asynchronous 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 handler
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 notification. The
SIGIO signal can have several meanings simultaneously. For example, it
can signify that a descriptor generated SIGIO and an asynchronous
operation completed. Further, issuing an asynchronous request
successfully guarantees that space exists to queue the completion

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 outstanding
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


The aioread() and aiowrite() functions will fail if:

The number of asynchronous requests that the system can handle
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 outstanding
asynchronous request.

The offset argument is not a valid offset for this file system

Memory resources are unavailable to initiate request.


The aioread() and aiowrite() functions have transitional interfaces for
64-bit file offsets. See lf64(7).


See attributes(7) for descriptions of the following attributes:

|MT-Level | Safe |


close(2), execve(2), exit(2), llseek(2), lseek(2), open(2), read(2),
write(2), aiocancel(3C), aiowait(3C), attributes(7), lf64(7)

May 13, 2017 AIOREAD(3C)