disk: lookup volumes in disk.set_backend_for_existing_path

Seems like it should be doing this.
Make use of that helper in cloner afterwards

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/test_xmlparse.py

@@ -1587,6 +1587,23 @@ class XMLParseTest(unittest.TestCase):
         with self.assertRaises(ValueError):
             disk.validate()
 
+        # Ensure set_backend_for_existing_path resolves a path
+        # to its existing storage volume
+        xml = ("<disk type='file' device='disk'>"
+            "<source file='/dev/default-pool/default-vol'/>"
+            "</disk>")
+        conn = utils.URIs.open_testdriver_cached()
+        disk = virtinst.DeviceDisk(conn, parsexml=xml)
+        disk.set_backend_for_existing_path()
+        assert disk.get_vol_object()
+
+        # Verify set_backend_for_existing_path doesn't error
+        # for a variety of disks
+        dom = conn.lookupByName("test-many-devices")
+        guest = virtinst.Guest(conn, parsexml=dom.XMLDesc(0))
+        for disk in guest.devices.disk:
+            disk.set_backend_for_existing_path()
+
     def testGuestXMLDeviceMatch(self):
         """
         Test Guest.find_device and Device.compare_device

virtinst/cloner.py

@@ -194,8 +194,7 @@ class _CloneDiskInfo:
 
     def check_clonable(self):
         try:
-            # This forces DeviceDisk to resolve the storage backend
-            self.disk.path = self.disk.path
+            self.disk.set_backend_for_existing_path()
             if self.disk.wants_storage_creation():
                 raise ValueError(
                         _("Disk path '%s' does not exist.") % self.disk.path)

virtinst/devices/disk.py

@@ -675,6 +675,10 @@ class DeviceDisk(Device):
         if vol_object is None and path is None:
             path = self._get_xmlpath()
 
+        if path and not vol_object and not parent_pool:
+            (vol_object, parent_pool) = diskbackend.manage_path(
+                    self.conn, path)
+
         self._change_backend(path, vol_object, parent_pool)
 
     def set_local_disk_to_clone(self, disk, sparse):