dbg("next cluster %u", next);
next_sect_off = (next - 2) * vs->sectors_per_cluster;
next_off = (start_data_sect + next_sect_off) * sector_size;
dbg("next cluster %u", next);
next_sect_off = (next - 2) * vs->sectors_per_cluster;
next_off = (start_data_sect + next_sect_off) * sector_size;