AIOREAD(3)

NAME
aioread, aiowrite - asynchronous I/O operations

SYNOPSIS
#include <sys/asynch.h>

int aioread(fd, bufp, bufs, offset, whence, resultp)
int fd;
char *bufp;
int bufs;
int offset;
int whence;
aio_result_t *resultp;

int aiowrite(fd, bufp, bufs, offset, whence, resultp)
int fd;
char *bufp;
int bufs;
int offset;
int whence;
aio_result_t *resultp;

DESCRIPTION

aioread() initiates one asynchronous read(2V) 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 fd into the buffer pointed to by bufp.

aiowrite() initiates one asynchronous write(2V) 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 fd.

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 lseek(2V) 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. AIO_INPROGRESS is not a value used by the system so the client may detect a change in state by initializing aio_return to this value.

Notification of the completion of an asynchronous I/O operation may be obtained synchronously through the aiowait(3) function, or asynchronously through the signal mechanism. Asynchronous notification is accomplished by generating the SIGIO signal. 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(3) returns nothing (using a polling timeout) before returning from the signal handler, no asynchronous I/O notifications are lost. The aiowait(3) function is the only way to dequeue an asynchronous notification. Note: SIGIO may have several meanings simultaneously: for example, that a descriptor generated SIGIO and an asynchronous operation completed. Further, issuing an asynchronous request successfully guarantees that space exists to queue the completion notification.

close(2V), exit(2V) and execve(2V) will block until all pending asynchronous I/O operations can be cancelled by the system.

It is an error to use the same result buffer in more than one outstanding request. These structures may only be reused after the system has completed the operation.

RETURN VALUES

aioread() and aiowrite() return:

0   on success.

-1  on failure and set errno to indicate the error.

ERRORS

EBADF
    fd is not a valid file descriptor open for reading.

EFAULT
    At least one of bufp or resultp points to an address out side the address space of the requesting process.

EINVAL
    The parameter resultp is currently being used by an outstanding asynchronous request.

EPROCLIM
    The number of asynchronous requests that the system can handle at any one time has been exceeded

SEE ALSO
close(2V), execve(2V), exit(2V), lseek(2V), open(2V), read(2V), sigvec(2), write(2V), aiocancel(3), aiowait(3)