Node.js使用fs.renameSync报cross-device link not permitted错误

var Q = require('q');
var util = require('util');
var fs = require('fs');
var path = require('path');
var moment = require('moment');
var formidable = require('formidable');

var imageUpload = function (){
};

imageUpload.prototype.useFormParseCallback = function(req){
    var deferred = Q.defer();

    var form = new formidable.IncomingForm();
    form.parse(req, deferred.makeNodeResolver());
    return deferred.promise;
};

// 确保目录存在
// 如果指定的目录不存在则同步创建（多层次）
imageUpload.prototype.ensureUploadPathExist = function(uploadPath, mode){
    if (!fs.existsSync(uploadPath)){
        var pathtmp;
        uploadPath.split(path.sep).forEach(function(dirname) {
            if (pathtmp) {
                pathtmp = path.join(pathtmp, dirname);
            }
            else {
                pathtmp = dirname;
            }
            if (!fs.existsSync(pathtmp)) {
                if (!fs.mkdirSync(pathtmp, mode)) {
                    return false;
                }
            }
        });
    }

    return true;
};

imageUpload.prototype.uploadImage = function(req){
    var pathName = '/uploadImgs/';
    var uploadPath = path.join(__dirname, '../../public', pathName);

    this.ensureUploadPathExist(uploadPath);

    return this.useFormParseCallback(req).then(function(files){
        var file = files[1].imagefile;
        var fileType = file.type.split('/')[1];
        var newFileName = 'upload_' + moment().format('x') + Math.random().toString().substr(2, 10) + '.' + fileType;
        fs.renameSync(file.path, uploadPath + newFileName);
        return pathName + newFileName;
    });
};

module.exports = imageUpload;

var readStream = fs.createReadStream(file.path);
var writeStream = fs.createWriteStream(uploadPath + newFileName);
 
var deferred = Q.defer();
util.pump(readStream, writeStream, deferred.makeNodeResolver());
return deferred.promise.then(function() {
    fs.unlinkSync(file.path);
    return pathName + newFileName;
});