Refactor device drivers

[niklauslee]

Registering device drivers

// character devices
global.__chrdev['stdin'] = ... (object)
global.__chrdev['stdout'] = ... (object)

// block devices
global.__blkdev['fs'] = ... (object)
global.__blkdev['storage'] = ... (object)

// network devices
global.__netdev['eth0'] = ... (object)

Character Device Driver and Stream

Character device driver should implement Stream interface.

interface Stream extends EventListener {
  readableFlowing: boolean; // flowing mode when 'data' event attached?
  readableEnded: boolean;
  readable(): boolean; // true if readable stream
  read(length: number): Uint8Array|null; // returns null when no data to read
  // event 'data'
  // event 'end'
  writableEnded: boolean; // end() called
  writableFinished: boolean; // end() called and all data flushed
  writable(): boolean; // true if writable stream
  write(data: Uint8Array): boolean; // returns true when need 'drain' event
  end();
  // event 'drain'
  // event 'finish'
  destroy();
}

Process object

Solution for #461

process.stdin // returns global.__chrdev['stdin'];
process.stdout // returns global.__chrdev['stdout'];
process.stderr // returns global.__chrdev['stderr'];

File system

Need support configurations instead of calling method?
Event we support configs, we still need functions like mount(), register(), etc.

// file systems
global.__fs['lfs'] = ... (constructor)
global.__fs['fat'] = ... (constructor)

// mounts
global.__mount['/'] = {blkdev: 'fs', fs: 'lfs', mkfs: true}
// if no mounts, we don't need fs commands in REPL (e.g. .ls, .cd, .pwd, ...)

Do we need to support even this?

fs.readSync(fd, ...); // if fd = 0, read from global.__chrdev['stdin']
fs.writeSync(fd, ...); // if fd = 1, write to global.__chrdev['stdout']
// ...