Node.js调用fs.renameSync报错（Error: EXDEV, cross-device link not permitted）

 function upload(response,request){
 console.log("upload called");
 var form = new formidable.IncomingForm();
 console.log("about to parse");
 form.parse(request, function(error, fields, files) {
  console.log("parsing done");
  fs.renameSync(files.upload.path, "./tmp/test.jpg");
  response.writeHead(200, {"Content-Type": "text/html"});
  response.write("received image:<br/>");
  response.write("<img src='/show' />");
  response.end();
 });
 }

 function upload(response,request){
 console.log("upload called");
 var form = new formidable.IncomingForm();
 console.log("about to parse");
 form.parse(request, function(error, fields, files) {
  console.log("parsing done");

 // fs.renameSync(files.upload.path, "./tmp/test.jpg");
  var readStream=fs.createReadStream(files.upload.path);
  var writeStream=fs.createWriteStream("./tmp/test.jpg");
  readStream.pipe(writeStream);
  readStream.on('end',function(){
  fs.unlinkSync(files.upload.path);
  });

  response.writeHead(200, {"Content-Type": "text/html"});
  response.write("received image:<br/>");
  response.write("<img src='/show' />");
  response.end();
 });
 }

util.pump(readStream,writeStream, function() {
 fs.unlinkSync('files.upload.path');
});

 function upload(response,request){
 console.log("upload called");
 var form = new formidable.IncomingForm();
 form.uploadDir='tmp';
 console.log("about to parse");
 form.parse(request, function(error, fields, files) {
  console.log("parsing done");
  fs.renameSync(files.upload.path, "./tmp/test.jpg");
  response.writeHead(, {"Content-Type": "text/html"});
  response.write("received image:<br/>");
  response.write("<img src='/show' />");
  response.end();
 });
 }