Adds instance root disk size checks during resize

Fixes bug: #1163844

The Hyper-V driver does not support disk resizes to a smaller size.
This patch verifies the disk size compatibility before the migration
starts in order to avoid data losses.

Change-Id: Ie99bf8779d583e97b911c9a136cee1bca9a1ecdc

2 files changed, 24 insertions, 2 deletions

diff --git a/nova/virt/hyperv/migrationops.py b/nova/virt/hyperv/migrationops.py
index 07bf453e5..ff8651efe 100644
--- a/nova/virt/hyperv/migrationops.py
+++ b/nova/virt/hyperv/migrationops.py
@@ -95,11 +95,25 @@ class MigrationOps(object):
             LOG.exception(ex)
             LOG.error(_("Cannot cleanup migration files"))
 
+    def _check_target_instance_type(self, instance, instance_type):
+        new_root_gb = instance_type['root_gb']
+        curr_root_gb = instance['root_gb']
+
+        if new_root_gb < curr_root_gb:
+            raise vmutils.VHDResizeException(_("Cannot resize the root disk "
+                                               "to a smaller size. Current "
+                                               "size: %(curr_root_gb)s GB. "
+                                               "Requested size: "
+                                               "%(new_root_gb)s GB") %
+                                             locals())
+
     def migrate_disk_and_power_off(self, context, instance, dest,
                                    instance_type, network_info,
                                    block_device_info=None):
         LOG.debug(_("migrate_disk_and_power_off called"), instance=instance)
 
+        self._check_target_instance_type(instance, instance_type)
+
         self._vmops.power_off(instance)
 
         instance_name = instance["name"]
@@ -218,8 +232,8 @@ class MigrationOps(object):
                 curr_size = vhd_info['MaxInternalSize']
                 new_size = instance['root_gb'] * 1024 ** 3
                 if new_size < curr_size:
-                    raise vmutils.HyperVException(_("Cannot resize a VHD to a "
-                                                    "smaller size"))
+                    raise vmutils.VHDResizeException(_("Cannot resize a VHD "
+                                                       "to a smaller size"))
                 elif new_size > curr_size:
                     self._resize_vhd(root_vhd_path, new_size)
 
diff --git a/nova/virt/hyperv/vmutils.py b/nova/virt/hyperv/vmutils.py
index 45fea329d..680ec2d61 100644
--- a/nova/virt/hyperv/vmutils.py
+++ b/nova/virt/hyperv/vmutils.py
@@ -37,11 +37,19 @@ CONF = cfg.CONF
 LOG = logging.getLogger(__name__)
 
 
+# TODO(alexpilotti): Move the exceptions to a separate module
+# TODO(alexpilotti): Add more domain exceptions
 class HyperVException(exception.NovaException):
     def __init__(self, message=None):
         super(HyperVException, self).__init__(message)
 
 
+# TODO(alexpilotti): Add a storage exception base class
+class VHDResizeException(HyperVException):
+    def __init__(self, message=None):
+        super(HyperVException, self).__init__(message)
+
+
 class VMUtils(object):
 
     def __init__(self, host='.'):