system call waits for completion of an asynchronous I/O request.
returns the result of the function and sets
to point to the structure associated with the original request.
If an asynchronous I/O request is completed before
is called, it returns immediately with the completed request.
is a non-NULL pointer, it specifies a maximum interval to wait for a
asynchronous I/O request to complete.
is a NULL pointer,
To effect a poll, the
argument should be non-NULL, pointing to a zero-valued timeval structure.
system call also serves the function of
should not be called for the control block returned in