Lab10 File System

Large files

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

  if(bn < NDIRECT){
    if((addr = ip->addrs[bn]) == 0)
      ip->addrs[bn] = addr = balloc(ip->dev);
    return addr;
  }
  bn -= NDIRECT;
  //mycode
  //第一个非直接块
  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;
  }

  //第二个非直接块
  bn -= NINDIRECT;
  if(bn < NNINDIRECT){
    // Load 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;

    int index = bn / (BSIZE / sizeof(uint));
    if((addr = a[index]) == 0){
      a[index] = addr = balloc(ip->dev);
      log_write(bp);
    }
    brelse(bp);

    bp = bread(ip->dev, addr);
    a = (uint*)bp->data;

    index = bn % (BSIZE / sizeof(uint));
    if((addr = a[index]) == 0){
      a[index] = addr = balloc(ip->dev);
      log_write(bp);
    }
    brelse(bp);
    return addr;
  }

  panic("bmap: out of range");
}

void
itrunc(struct inode *ip)
{
  int i, j, k;
  struct buf *bp, *bp2;
  uint *a, *a2;

  for(i = 0; i < NDIRECT; i++){
    if(ip->addrs[i]){
      bfree(ip->dev, ip->addrs[i]);
      ip->addrs[i] = 0;
    }
  }

  //第一个非直接块
  if(ip->addrs[NDIRECT]){
    bp = bread(ip->dev, ip->addrs[NDIRECT]);
    a = (uint*)bp->data;
    for(j = 0; j < NINDIRECT; j++){
      if(a[j])
        bfree(ip->dev, a[j]);
    }
    brelse(bp);
    bfree(ip->dev, ip->addrs[NDIRECT]);
    ip->addrs[NDIRECT] = 0;
  }

  //第二个非直接块
  if(ip->addrs[NDIRECT + 1]){
    bp = bread(ip->dev, ip->addrs[NDIRECT + 1]);
    a = (uint*)bp->data;

    for(j = 0; j < NINDIRECT; j++){
      if(a[j]) {
        bp2 = bread(ip->dev, a[j]);
        a2 = (uint*)bp2->data;
        for(k = 0; k < NINDIRECT; k++){
          if(a2[k])
            bfree(ip->dev, a2[k]);
        }
        brelse(bp2);
        bfree(ip->dev, a[j]);
      }
    }
    brelse(bp);
    bfree(ip->dev, ip->addrs[NDIRECT]);
    ip->addrs[NDIRECT] = 0;
  }

  ip->size = 0;
  iupdate(ip);
}

Symbolic links

uint
sys_symlink() {
  char target[MAXPATH], path[MAXPATH];
  if(argstr(0, target, MAXPATH) < 0 || argstr(1, path, MAXPATH) < 0)
    return -1;

  struct inode* ip;

  begin_op();
  ip = create(path, T_SYMLINK, 0, 0);
  if(ip == 0){
    end_op();
    return -1;
  }

  if((writei(ip, 0, (uint64)target, 0, MAXPATH)) == 0){
    iunlockput(ip);
    end_op();
    return -1;
  }
  iunlockput(ip);    //createilock，在这里释放
  end_op();
  return 0;
}

if(!(omode & O_NOFOLLOW)){
    int count = 0;
    struct inode* nextip;

    while(count < 10 && ip->type == T_SYMLINK){
      count++;
      if((readi(ip, 0, (uint64)path, 0, MAXPATH)) == 0){
        iunlockput(ip);
        end_op();
        return -1;
      }
      if((nextip = namei(path)) == 0){
        iunlockput(ip);
        end_op();
        return -1;
      }
        
      iunlockput(ip);
      ip = nextip;
      ilock(ip);
    }
    if(count >= 10){     //注意计数
      iunlockput(ip);
      end_op();
      return -1;
    }
  }