Merge lp:~niedbalski/charm-helpers/fix-lp1510666 into lp:charm-helpers

[Jorge Niedbalski]

Adds the is_mapped_loopback_device method for fixing LP: #1510666

=== modified file 'charmhelpers/contrib/storage/linux/loopback.py'
--- charmhelpers/contrib/storage/linux/loopback.py	2015-01-22 06:06:03 +0000
+++ charmhelpers/contrib/storage/linux/loopback.py	2015-11-02 19:48:58 +0000
@@ -76,3 +76,13 @@
         check_call(cmd)
 
     return create_loopback(path)
+
+
+def is_mapped_loopback_device(device):
+    """
+    Checks if a given device name is an existing/mapped loopback device.
+    :param device: str: Full path to the device (eg, /dev/loop1).
+    :returns: str: Path to the backing file if is a loopback device
+    empty string otherwise
+    """
+    return loopback_devices().get(device, "")

=== modified file 'tests/contrib/storage/test_linux_storage_loopback.py'
--- tests/contrib/storage/test_linux_storage_loopback.py	2013-07-18 00:46:25 +0000
+++ tests/contrib/storage/test_linux_storage_loopback.py	2015-11-02 19:48:58 +0000
@@ -73,3 +73,10 @@
             result = loopback.create_loopback('/tmp/foo')
             check_call.assert_called_with(['losetup', '--find', '/tmp/foo'])
             self.assertEquals(result, '/dev/loop0')
+
+    @patch.object(loopback, 'loopback_devices')
+    def test_create_is_mapped_loopback_device(self, devs):
+        devs.return_value = {'/dev/loop0': "/tmp/manco"}
+        self.assertEquals(loopback.is_mapped_loopback_device("/dev/loop0"),
+                          "/tmp/manco")
+        self.assertFalse(loopback.is_mapped_loopback_device("/dev/loop1"))