xv6 big file

xv6 Big file

实验步骤：
1、修改Makefile文件：将CPUS的值设为1，,并添加如下语句。目的是加快xv6创建大文件时的qemu的运行速度：

2、修改param.h文件，将文件系统的最大数据块数设置为20000：

3、下载big.c文件放入xv6的目录下，并在Makefile文件中的UPROGS列表中增加对big命令的引用：

4、启动xv6，输入big命令，显示“wrote 140 sectors”，说明所有的准备工作已完成：

5、修改fs.c中的bmap()函数如下：

static uintbmap(struct inode *ip, uint bn){  uint addr, *a, *indirect, *double_indirect,indirect_idx, double_indirect_idx;  struct buf *bp, *bp2;  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 ifnecessary.    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 < NINDIRECT*NINDIRECT) {    // Load first indirect block, allocating ifnecessary.    if((addr = ip->addrs[NDIRECT + 1]) == 0)      ip->addrs[NDIRECT + 1] = addr =balloc(ip->dev);    bp = bread(ip->dev, addr);    indirect = (uint *) bp->data;    indirect_idx = bn / NINDIRECT;    if ((addr = indirect[indirect_idx]) == 0) {      addr = indirect[indirect_idx] =balloc(ip->dev);      log_write(bp);    }    bp2 = bread(ip->dev, addr);    double_indirect = (uint *) bp2->data;    double_indirect_idx = bn % NINDIRECT;    if((addr = double_indirect[double_indirect_idx]) == 0) {      addr =double_indirect[double_indirect_idx] = balloc(ip->dev);      log_write(bp2);    }    brelse(bp2);    brelse(bp);    return addr;  }  panic("bmap: out of range");}

6、打开fs.h文件，将NDIRECT的值改为11，对应的架构数据块地址的索引由加1变为加2，最后将MAXFILE修改成如下值：

7、保存后重新启动xv6，输入big命令，得到如下运行结果说明实验成功：