diff --git a/lib/files/cache/cache.php b/lib/files/cache/cache.php
index cba48e4dbe..138a5e6e63 100644
--- a/lib/files/cache/cache.php
+++ b/lib/files/cache/cache.php
@@ -234,7 +234,7 @@ class Cache {
 		$entry = $this->get($file);
 		if ($entry['mimetype'] === 'httpd/unix-directory') {
 			$children = $this->getFolderContents($file);
-			foreach($children as $child){
+			foreach ($children as $child) {
 				$this->remove($child['path']);
 			}
 		}
@@ -325,7 +325,9 @@ class Cache {
 		$query = \OC_DB::prepare('SELECT `size` FROM `*PREFIX*filecache` WHERE `parent` = ? AND `storage` = ?');
 		$result = $query->execute(array($id, $this->storageId));
 		$totalSize = 0;
+		$hasChilds = 0;
 		while ($row = $result->fetchRow()) {
+			$hasChilds = true;
 			$size = (int)$row['size'];
 			if ($size === -1) {
 				$totalSize = -1;
@@ -335,7 +337,9 @@ class Cache {
 			}
 		}
 
-		$this->update($id, array('size' => $totalSize));
+		if ($hasChilds) {
+			$this->update($id, array('size' => $totalSize));
+		}
 		return $totalSize;
 	}
 
diff --git a/lib/files/cache/watcher.php b/lib/files/cache/watcher.php
new file mode 100644
index 0000000000..f04ca9b465
--- /dev/null
+++ b/lib/files/cache/watcher.php
@@ -0,0 +1,70 @@
+<?php
+/**
+ * Copyright (c) 2012 Robin Appelman <icewind@owncloud.com>
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+namespace OC\Files\Cache;
+
+/**
+ * check the storage backends for updates and change the cache accordingly
+ */
+class Watcher {
+	/**
+	 * @var \OC\Files\Storage\Storage $storage
+	 */
+	private $storage;
+
+	/**
+	 * @var Cache $cache
+	 */
+	private $cache;
+
+	/**
+	 * @var Scanner $scanner;
+	 */
+	private $scanner;
+
+	/**
+	 * @param \OC\Files\Storage\Storage $storage
+	 */
+	public function __construct(\OC\Files\Storage\Storage $storage) {
+		$this->storage = $storage;
+		$this->cache = $storage->getCache();
+		$this->scanner = $storage->getScanner();
+	}
+
+	/**
+	 * check $path for updates
+	 *
+	 * @param string $path
+	 */
+	public function checkUpdate($path) {
+		$cachedEntry = $this->cache->get($path);
+		if ($this->storage->hasUpdated($path, $cachedEntry['mtime'])) {
+			if ($cachedEntry['mimetype'] === 'httpd/unix-directory') {
+				$this->scanner->scan($path, Scanner::SCAN_SHALLOW);
+				$this->cleanFolder($path);
+			} else {
+				$this->scanner->scanFile($path);
+			}
+			$this->scanner->correctFolderSize($path);
+		}
+	}
+
+	/**
+	 * remove deleted files in $path from the cache
+	 *
+	 * @param string $path
+	 */
+	public function cleanFolder($path) {
+		$cachedContent = $this->cache->getFolderContents($path);
+		foreach ($cachedContent as $entry) {
+			if (!$this->storage->file_exists($entry['path'])) {
+				$this->cache->remove($entry['path']);
+			}
+		}
+	}
+}
diff --git a/tests/lib/files/cache/watcher.php b/tests/lib/files/cache/watcher.php
new file mode 100644
index 0000000000..a7076d9b0b
--- /dev/null
+++ b/tests/lib/files/cache/watcher.php
@@ -0,0 +1,86 @@
+<?php
+/**
+ * Copyright (c) 2012 Robin Appelman <icewind@owncloud.com>
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+namespace Test\Files\Cache;
+
+class Watcher extends \PHPUnit_Framework_TestCase {
+
+	/**
+	 * @var \OC\Files\Storage\Storage[] $storages;
+	 */
+	private $storages = array();
+
+	public function setUp() {
+		\OC\Files\Filesystem::clearMounts();
+	}
+
+	public function tearDown() {
+		foreach ($this->storages as $storage) {
+			$cache = $storage->getCache();
+			$ids = $cache->getAll();
+			\OC\Files\Cache\Permissions::removeMultiple($ids, \OC_User::getUser());
+			$cache->clear();
+		}
+	}
+
+	function testWatcher() {
+		$storage = $this->getTestStorage();
+		$cache = $storage->getCache();
+		$updater = new \OC\Files\Cache\Watcher($storage);
+
+		//set the mtime to the past so it can detect an mtime change
+		$cache->put('', array('mtime' => 10));
+
+		$this->assertTrue($cache->inCache('folder/bar.txt'));
+		$this->assertTrue($cache->inCache('folder/bar2.txt'));
+
+		$this->assertFalse($cache->inCache('bar.test'));
+		$storage->file_put_contents('bar.test', 'foo');
+		$updater->checkUpdate('');
+		$this->assertTrue($cache->inCache('bar.test'));
+		$cachedData = $cache->get('bar.test');
+		$this->assertEquals(3, $cachedData['size']);
+
+		$cache->put('bar.test', array('mtime' => 10));
+		$storage->file_put_contents('bar.test', 'test data');
+
+		$updater->checkUpdate('bar.test');
+		$cachedData = $cache->get('bar.test');
+		$this->assertEquals(9, $cachedData['size']);
+
+		$cache->put('folder', array('mtime' => 10));
+
+		$storage->unlink('folder/bar2.txt');
+		$updater->checkUpdate('folder');
+
+		$this->assertTrue($cache->inCache('folder/bar.txt'));
+		$this->assertFalse($cache->inCache('folder/bar2.txt'));
+	}
+
+	/**
+	 * @param bool $scan
+	 * @return \OC\Files\Storage\Storage
+	 */
+	private function getTestStorage($scan = true) {
+		$storage = new \OC\Files\Storage\Temporary(array());
+		$textData = "dummy file data\n";
+		$imgData = file_get_contents(\OC::$SERVERROOT . '/core/img/logo.png');
+		$storage->mkdir('folder');
+		$storage->file_put_contents('foo.txt', $textData);
+		$storage->file_put_contents('foo.png', $imgData);
+		$storage->file_put_contents('folder/bar.txt', $textData);
+		$storage->file_put_contents('folder/bar2.txt', $textData);
+
+		if ($scan) {
+			$scanner = $storage->getScanner();
+			$scanner->scan('');
+		}
+		$this->storages[] = $storage;
+		return $storage;
+	}
+}
diff --git a/tests/lib/files/view.php b/tests/lib/files/view.php
index 5144fb1caa..8ff03963e4 100644
--- a/tests/lib/files/view.php
+++ b/tests/lib/files/view.php
@@ -20,6 +20,8 @@ class View extends \PHPUnit_Framework_TestCase {
 	public function tearDown() {
 		foreach ($this->storages as $storage) {
 			$cache = $storage->getCache();
+			$ids = $cache->getAll();
+			\OC\Files\Cache\Permissions::removeMultiple($ids, \OC_User::getUser());
 			$cache->clear();
 		}
 	}