MIT6.828 Fall2018 筆記 - Homework 10: bigger files for xv6

Homework: bigger files for xv6

修改param.h：

#define FSSIZE       20000  // size of file system in blocks

修改fs.h：

#define NDIRECT 11
#define NINDIRECT (BSIZE / sizeof(uint))
#define NDINDIRECT (NINDIRECT * NINDIRECT)
#define MAXFILE (NDIRECT + NINDIRECT + NDINDIRECT)

struct dinode {
// -- 省略 --
  uint addrs[NDIRECT+2];
};

修改file.h：

struct inode {
// -- 省略 --
  uint addrs[NDIRECT+2];
};

修改fs.c：

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;

  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 < NDINDIRECT) {
    uint bn1 = bn / NINDIRECT;
    uint bn2 = bn % NINDIRECT;
    struct buf *bp2;
    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[bn1]) == 0) {
      a[bn1] = addr = balloc(ip->dev);
      log_write(bp);
    }

    bp2 = bread(ip->dev, addr);
    a = (uint *)bp2->data;
    if ((addr = a[bn2]) == 0) {
      a[bn2] = addr = balloc(ip->dev);
      log_write(bp2);
    }

    brelse(bp2);
    brelse(bp);
    return addr;
  }

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

而後刪除fs.img文件，再make clean qemu：

init: starting sh
$ big
.....................................................................................................................................................................
wrote 16523 sectors
done; ok
$