The information copied to the pmmcfinfo parameter consists of an MMCFINFO structure followed by the variable-length arrays: aulExHdrFldUsage, aulExEntFldUsage, and aulExHdrField.

To find out how large a buffer the user needs to allocate, call mmioCFGetInfo with the cBytes equal to the size of a ULONG. This will return the first field of the CTOC header, which happens to be the size of the header. This size can be used as cBytes on the subsequent call.