在這次作業中我們將實現增大xv6檔案大小的最大值。目前xv6檔案被限制擁有140sectors(扇區)，這是由於1個xv6的inode含有12直接塊序號和1個間接塊序號(指向128個塊序號)，故此總共12+128=140。而我們的任務就是改變實現支援2層間接塊序號(每個含有128個原先的間接塊序號)，導致總共擁有11+128+128*128=16523個扇區，大約8.5M大小。
　　修改mkfs.c檔案，以使檔案系統支援更大的檔案大小。

int nblocks = 21049;
int nlog = LOGSIZE;
int ninodes = 200;
int size = 21113

　　原先inode的結構圖：
　　

static uint
bmap(struct inode *ip, uint bn)
{
  uint addr, *a, *b;
  struct buf *bp, *bnp;

  if(bn < NDIRECT){
    if((addr = ip->addrs[bn]) == 0)
      ip->addrs[bn] = addr = balloc(ip->dev);
    return addr;
  }
  bn -= NDIRECT
 
;

  if(bn < NINDIRECT){
    // Load indirect block, allocating if necessary.
    if((addr = ip->addrs[NDIRECT]) == 0)
      ip->addrs[NDIRECT] = addr = balloc(ip->dev);
    bp = bread(ip->dev, addr);
    a = (uint*)bp->data;
    if((addr = a[bn]) == 0){
      a[bn] = addr = balloc(ip->dev);
      log_write(bp);
    }
　　    brelse(bp);
    return addr;
  }
  bn -= NINDIRECT
 
;

  if(bn < NDBINDIRECT){
    // Load single indirect block, allocating if necessary.
    if((addr = ip->addrs[NDIRECT+1]) == 0)
      ip->addrs[NDIRECT+1] = addr = balloc(ip->dev);
    bp = bread(ip->dev, addr);
    a = (uint*)bp->data;
    if((addr = a[bn/NINDIRECT]) == 0){
      a[bn/NINDIRECT] = addr = balloc(ip->dev);
      log_write(bp);
    }
    // Load double indirect block, allocating if necessary.
    bnp = bread(ip->dev, addr);
    b = (uint*)bnp->data;
    if ((addr = b[bn%NINDIRECT]) == 0){
      b[bn%NINDIRECT] = addr = balloc(ip->dev);
      log_write(bnp);
    }
    brelse(bnp);
    brelse(bp);
    return addr;
  }
}

　　跟分頁機制差不多，判斷塊序號落在哪個區域，若在直接塊序號(0-10)則直接獲取訪問；若在1層間接塊，獲取1層間接塊的內容，然後再從中得到序號對應的具體物理塊。