Hello, I have modified my aioError and aioReturn to hopefully be more in line with the actual aio_error and aio_return signatures, respectively. In the first implementation I had suffered a serious brain f**t ... oh well ..... The implementations below are still somewhat preliminary. Not seemingly rocket science .... I am still not getting a correct count from aioReturn .. should be 20 but I get 0! I have a C program which behaves properly giving 20 for aio_return! grrrrrr! aioReturn :: AIOCB -> IO (AIOCB, ByteCount) aioReturn aiocb = do allocaBytes (#const sizeof(struct aiocb)) $ \ p_aiocb -> do poke p_aiocb aiocb -- DO A PEEK HERE!!!!! -- count <- throwErrnoIfMinus1 "aioReturn" (c_aio_return p_aiocb) count <- (c_aio_return p_aiocb) putStrLn ("count -> " ++ (show count)) aiocb <- peek p_aiocb putStrLn "aioReturn" aiocb1 <- peek p_aiocb dumpAIOCB aiocb1 return (aiocb, fromIntegral count) foreign import ccall safe "aio.h aio_return" c_aio_return :: Ptr AIOCB -> IO CInt aioError :: AIOCB -> IO (Errno) aioError aiocb = do allocaBytes (#const sizeof(struct aiocb)) $ \ p_aiocb -> do poke p_aiocb aiocb --throwErrnoIfMinus1 "aioError" (c_aio_error p_aiocb) errno <- (c_aio_error p_aiocb) putStrLn ("errno -> " ++ (show errno)) putStrLn "aioError" aiocb1 <- peek p_aiocb dumpAIOCB aiocb1 return (Errno errno) foreign import ccall safe "aio.h aio_error" c_aio_error :: Ptr AIOCB -> IO CInt I added an internal helper function dumpAIOCB to print out the aiocb at points for sanity checking!! dumpAIOCB :: AIOCB -> IO () dumpAIOCB (AIOCB aioFd aioLioOpcode aioReqPrio aioOffset aioBuf aioBytes aioSigevent) = do putStrLn "aiocb dump" putStrLn ("fd => " ++ (show aioFd)) putStrLn ("opcode => " ++ (show aioLioOpcode)) putStrLn ("prio => " ++ (show aioReqPrio)) putStrLn ("offset => " ++ (show aioOffset)) -- aioBuf putStrLn ("nbytes => " ++ (show aioBytes) ++ "\n") -- aioSigevent Kind regards, Vasili