PHP文件上传.检索URL

我正在使用PHP上传一个文件，然后我想获取它的URL，以便将其添加到数据库中。如何将新文件的URL获取到可以通过MySQL插入的变量中？

<?php
// Configuration - Your Options
  $allowed_filetypes = array('.jpg','.gif','.bmp','.png'); // These will be the types     of file that will pass the validation.
  $max_filesize = 524288; // Maximum filesize in BYTES (currently 0.5MB).
  $upload_path = './files/'; // The place the files will be uploaded to (currently a 'files' directory).
$filename = $_FILES['userfile']['name']; // Get the name of the file (including file   extension).
$ext = substr($filename, strpos($filename,'.'), strlen($filename)-1); // Get the extension from the filename.
// Check if the filetype is allowed, if not DIE and inform the user.
if(!in_array($ext,$allowed_filetypes))
  die('The file you attempted to upload is not allowed.');
// Now check the filesize, if it is too large then DIE and inform the user.
if(filesize($_FILES['userfile']['tmp_name']) > $max_filesize)
  die('The file you attempted to upload is too large.');
// Check if we can upload to the specified path, if not DIE and inform the user.
if(!is_writable($upload_path))
  die('You cannot upload to the specified directory, please CHMOD it to 777.');
// Upload the file to your specified path.
if(move_uploaded_file($_FILES['userfile']['tmp_name'],$upload_path . $filename))
     echo 'Your file upload was successful, view the file <a href="' . $upload_path . $filename . '" title="Your File">here</a>'; 
// It worked.
  else
     echo 'There was an error during the file upload.  Please try again.'; // It failed :(.
?>