The return value of ibstop() is counter-intuitive. On successfully aborting an asynchronous operation, the ERR bit is set in ibsta, and iberr is set to EABO. If the ERR bit is not set in ibsta, then there was no asynchronous i/o operation in progress. If the function failed, the ERR bit will be set and iberr will be set to some value other than EABO.
The value of ibsta is returned.