Return
codes indicating success or type of failure. If the function succeeds,
the number of bytes copied is returned. A NULL is returned for a failure.
Additional error information is stored in the ulErrorRet field of
MMIOINFO as follows:
MMIOERR_INVALID_PARAMETER
The parameter passed
was invalid. For this function, a NULL pmmcfinfo is invalid. cBytes
must be greater than 0.
MMIOERR_WRITE_ONLY_FILE
File not opened in read mode.
MMIOERR_INTERNAL_SYSTEM
The operation failed due to an internal system
error.