MODE_HEADER_LENGTH
pgo = MODE_HEADER_LENGTH + (STp->buffer)->b_data[MH_OFF_BDESCS_LENGTH];
mpoffs = MODE_HEADER_LENGTH + b_data[MH_OFF_BDESCS_LENGTH];
result = (STp->buffer)->b_data[MODE_HEADER_LENGTH +
pgo = MODE_HEADER_LENGTH + bp[MH_OFF_BDESCS_LENGTH];