Check QCOW2 image size during root disk creation

glance can only tell us the size of the file, not the virtual
size of the QCOW2. As such we need to check the virtual size of
the image once its cached and ensure it's <= to the flavor's
root disk size.

Change-Id: I833467284126557eb598b8350a84e10c06292fa9
Fixes: bug 1177830
(cherry picked from commit 44a8aba)

nova/tests/test_imagebackend.py

@@ -17,6 +17,7 @@
 
 import os
 
+from nova import exception
 from nova import flags
 from nova import test
 from nova.tests import fake_libvirt_utils
@@ -190,7 +191,10 @@ def test_create_image_with_size(self):
         fn = self.prepare_mocks()
         fn(target=self.TEMPLATE_PATH)
         self.mox.StubOutWithMock(os.path, 'exists')
+        self.mox.StubOutWithMock(imagebackend.disk, 'get_disk_size')
         os.path.exists(self.QCOW2_BASE).AndReturn(False)
+        imagebackend.disk.get_disk_size(self.TEMPLATE_PATH
+                                       ).AndReturn(self.SIZE)
         imagebackend.libvirt_utils.copy_image(self.TEMPLATE_PATH,
                                               self.QCOW2_BASE)
         imagebackend.disk.extend(self.QCOW2_BASE, self.SIZE)
@@ -203,11 +207,25 @@ def test_create_image_with_size(self):
 
         self.mox.VerifyAll()
 
+    def test_create_image_too_small(self):
+        self.mox.StubOutWithMock(imagebackend.disk, 'get_disk_size')
+        imagebackend.disk.get_disk_size(self.TEMPLATE_PATH
+                                       ).AndReturn(self.SIZE)
+        self.mox.ReplayAll()
+
+        image = self.image_class(self.INSTANCE, self.NAME)
+        self.assertRaises(exception.ImageTooLarge, image.create_image, None,
+                          self.TEMPLATE_PATH, 1)
+        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')
+        self.mox.StubOutWithMock(imagebackend.disk, 'get_disk_size')
         os.path.exists(self.QCOW2_BASE).AndReturn(True)
+        imagebackend.disk.get_disk_size(self.TEMPLATE_PATH
+                                       ).AndReturn(self.SIZE)
         imagebackend.libvirt_utils.create_cow_image(self.QCOW2_BASE,
                                                     self.PATH)
         self.mox.ReplayAll()

nova/virt/libvirt/imagebackend.py

@@ -19,14 +19,17 @@
 import contextlib
 import os
 
+from nova import exception
 from nova import flags
 from nova.openstack.common import cfg
 from nova.openstack.common import excutils
+from nova.openstack.common import log as logging
 from nova import utils
 from nova.virt.disk import api as disk
 from nova.virt.libvirt import config
 from nova.virt.libvirt import utils as libvirt_utils
 
+
 __imagebackend_opts = [
     cfg.StrOpt('libvirt_images_type',
             default='default',
@@ -46,6 +49,8 @@
 FLAGS = flags.FLAGS
 FLAGS.register_opts(__imagebackend_opts)
 
+LOG = logging.getLogger(__name__)
+
 
 class Image(object):
     __metaclass__ = abc.ABCMeta
@@ -170,6 +175,13 @@ def copy_qcow2_image(base, target, size):
                         disk.extend(qcow2_base, size)
             libvirt_utils.create_cow_image(qcow2_base, target)
 
+        # NOTE(cfb): Having a flavor that sets the root size to 0 and having
+        #            nova effectively ignore that size and use the size of the
+        #            image is considered a feature at this time, not a bug.
+        if size and size < disk.get_disk_size(base):
+            LOG.error('%s virtual size larger than flavor root disk size %s' %
+                      (base, size))
+            raise exception.ImageTooLarge()
         prepare_template(target=base, *args, **kwargs)
         with utils.remove_path_on_error(self.path):
             copy_qcow2_image(base, self.path, size)