aio_error —
retrieve error status of asynchronous I/O operation
  (REALTIME)
POSIX Real-time Library (librt, -lrt)
#include <aio.h>
int
  
  aio_error(const
    struct aiocb *aiocbp);
The aio_error() system call returns the error status of
  the asynchronous I/O request associated with the structure pointed to by
  aiocbp.
If the asynchronous I/O request has completed successfully,
  aio_error() returns 0. If the request has not yet
  completed, EINPROGRESS is returned. If the request has
  completed unsuccessfully the error status is returned as described in
  read(2),
  write(2), or
  fsync(2). On failure,
  aio_error() returns -1 and sets
  errno to indicate the error condition.
The aio_error() system call will fail if:
  - [EINVAL]
- The aiocb argument does not reference an outstanding
      asynchronous I/O request.
Theaio_error() system call is expected to conform to
  the IEEE Std 1003.1-2001 (“POSIX.1”)
  standard.
The aio_error() system call first appeared in
  NetBSD 5.0.