Notification (SIGIO)

When an asynchronous I/O call returns successfully, the I/O operation has only been queued, waiting to be done. The actual operation also has a return value and a potential error identifier, the values that would have been returned to the caller as the result of a synchronous call. When the I/O is finished, the return value and error value are stored at a location given by the user at the time of the request as a pointer to an aio_result_t. The structure of the aio_result_t is defined in <sys/asynch.h>:

typedef struct aio_result_t {
 	ssize_t	aio_return; /* return value of read or write */
 	int 		aio_errno;  /* errno generated by the IO */
 } aio_result_t;

When aio_result_t has been updated, a SIGIO signal is delivered to the process that made the I/O request.

Note that a process with two or more asynchronous I/O operations pending has no certain way to determine which request, if any, is the cause of the SIGIO signal. A process receiving a SIGIO should check all its conditions that could be generating the SIGIO signal.