块设备、inode 与超级块设计

// 运行环境：Node.js 14+
// 保存为 aj-l9.js，执行：node aj-l9.js
const BLOCK = 16 // 演示用小块大小
class MiniFS {
  constructor(totalBlocks) {
    this.super = { magic: 0x1234, totalBlocks, freeBitmap: new Array(totalBlocks).fill(1) } // 1=空闲
    this.blocks = Array.from({ length: totalBlocks }, () => Buffer.alloc(BLOCK))
    this.inodes = {} // id -> {size, blocks:[...]}
    this.nextInode = 1
  }
  allocBlock() {
    const i = this.super.freeBitmap.indexOf(1)
    if (i === -1) throw new Error('磁盘满')
    this.super.freeBitmap[i] = 0
    return i
  }
  writeFile(name, content) {
    const data = Buffer.from(content)
    const blocks = []
    for (let off = 0; off < data.length; off += BLOCK) {
      const b = this.allocBlock()
      data.copy(this.blocks[b], 0, off, off + BLOCK)
      blocks.push(b)
    }
    this.inodes[name] = { size: data.length, blocks }
    return this.nextInode++
  }
  readFile(name) {
    const inode = this.inodes[name]
    const out = Buffer.alloc(inode.size)
    let w = 0
    for (const b of inode.blocks) { this.blocks[b].copy(out, w); w += BLOCK }
    return out.slice(0, inode.size).toString()
  }
}

// 调用示例
const fs = new MiniFS(8)
fs.writeFile('hello.txt', '你好，文件系统!')
console.log(fs.readFile('hello.txt')) // 你好，文件系统!