libvirt: Skip intermediate base files with qcow2.

Instead of having two files in _base (the original and a resized
copy), let's just keep the originals and resize with the qcow2
image in the instance's directory. This will reduce the size of
_base and simplify cleanup. This also simplifies resizing of
instance disk images later.

Resolves bug 1087031.

Change-Id: Id91426e3cb9f75f31339b5156785e3782a4cb98f

nova/tests/test_imagebackend.py

@@ -196,26 +196,9 @@ def test_create_image_with_size(self):
         fn = self.prepare_mocks()
         fn(target=self.TEMPLATE_PATH)
         self.mox.StubOutWithMock(os.path, 'exists')
-        os.path.exists(self.QCOW2_BASE).AndReturn(False)
-        imagebackend.libvirt_utils.copy_image(self.TEMPLATE_PATH,
-                                              self.QCOW2_BASE)
-        imagebackend.disk.extend(self.QCOW2_BASE, self.SIZE)
-        imagebackend.libvirt_utils.create_cow_image(self.QCOW2_BASE,
-                                                    self.PATH)
-        self.mox.ReplayAll()
-
-        image = self.image_class(self.INSTANCE, self.NAME)
-        image.create_image(fn, self.TEMPLATE_PATH, self.SIZE)
-
-        self.mox.VerifyAll()
-
-    def test_create_image_with_size_template_exists(self):
-        fn = self.prepare_mocks()
-        fn(target=self.TEMPLATE_PATH)
-        self.mox.StubOutWithMock(os.path, 'exists')
-        os.path.exists(self.QCOW2_BASE).AndReturn(True)
-        imagebackend.libvirt_utils.create_cow_image(self.QCOW2_BASE,
+        imagebackend.libvirt_utils.create_cow_image(self.TEMPLATE_PATH,
                                                     self.PATH)
+        imagebackend.disk.extend(self.PATH, self.SIZE)
         self.mox.ReplayAll()
 
         image = self.image_class(self.INSTANCE, self.NAME)

nova/virt/libvirt/imagebackend.py

@@ -177,15 +177,9 @@ def create_image(self, prepare_template, base, size, *args, **kwargs):
         @lockutils.synchronized(base, 'nova-', external=True,
                                 lock_path=self.lock_path)
         def copy_qcow2_image(base, target, size):
-            qcow2_base = base
+            libvirt_utils.create_cow_image(base, target)
             if size:
-                size_gb = size / (1024 * 1024 * 1024)
-                qcow2_base += '_%d' % size_gb
-                if not os.path.exists(qcow2_base):
-                    with utils.remove_path_on_error(qcow2_base):
-                        libvirt_utils.copy_image(base, qcow2_base)
-                        disk.extend(qcow2_base, size)
-            libvirt_utils.create_cow_image(qcow2_base, target)
+                disk.extend(target, size)
 
         prepare_template(target=base, *args, **kwargs)
         with utils.remove_path_on_error(self.path):