XenAPI: Fix race-condition with cached images.

The core problem is that XenServer's `VDI.copy` call drops the
destination file directly into the SR. This means that half-completed
files are visible with no way to distinguish these from fully-copied
files.

We had some code that attempted to mitigate this issue by checking
physical_utilisation against an expected value. The problem with this
code is that it didn't account for VDI chaining where the
physical_utilisation would not necessarily match the parent.

The net effect of this was that 'cloned' VDIs would never be found
because their physical_utilisation was far below what was expected.

The work around is to create our own `_safe_copy_vdi` which is isolated
and atomic. Long term, `VDI.copy` should be fixed so that half-completed
files are never stored in the SR.

Change-Id: I6eb3cb5259f9ee1c7394e58f76105a8b39bfc720

2 files changed, 66 insertions, 0 deletions

diff --git a/plugins/xenserver/xenapi/contrib/rpmbuild/SPECS/openstack-xen-plugins.spec b/plugins/xenserver/xenapi/contrib/rpmbuild/SPECS/openstack-xen-plugins.spec
index 8f4415311..63b5e71d3 100644
--- a/plugins/xenserver/xenapi/contrib/rpmbuild/SPECS/openstack-xen-plugins.spec
+++ b/plugins/xenserver/xenapi/contrib/rpmbuild/SPECS/openstack-xen-plugins.spec
@@ -33,6 +33,7 @@ rm -rf $RPM_BUILD_ROOT
 /etc/xapi.d/plugins/kernel
 /etc/xapi.d/plugins/migration
 /etc/xapi.d/plugins/pluginlib_nova.py
+/etc/xapi.d/plugins/workarounds
 /etc/xapi.d/plugins/xenhost
 /etc/xapi.d/plugins/xenstore.py
 /etc/xapi.d/plugins/utils.py
diff --git a/plugins/xenserver/xenapi/etc/xapi.d/plugins/workarounds b/plugins/xenserver/xenapi/etc/xapi.d/plugins/workarounds
new file mode 100755
index 000000000..611436539
--- /dev/null
+++ b/plugins/xenserver/xenapi/etc/xapi.d/plugins/workarounds
@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+# Copyright (c) 2012 Openstack, LLC
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""Handle the uploading and downloading of images via Glance."""
+
+import cPickle as pickle
+try:
+    import json
+except ImportError:
+    import simplejson as json
+import os
+import shutil
+
+import XenAPIPlugin
+
+import utils
+
+#FIXME(sirp): should this use pluginlib from 5.6?
+from pluginlib_nova import *
+configure_logging('hacks')
+
+
+def _copy_vdis(sr_path, staging_path, vdi_uuids):
+    seq_num = 0
+    for vdi_uuid in vdi_uuids:
+        src = os.path.join(sr_path, "%s.vhd" % vdi_uuid)
+        dst = os.path.join(staging_path, "%d.vhd" % seq_num)
+        shutil.copyfile(src, dst)
+        seq_num += 1
+
+
+def safe_copy_vdis(session, args):
+    params = pickle.loads(exists(args, 'params'))
+    sr_path = params["sr_path"]
+    vdi_uuids = params["vdi_uuids"]
+    uuid_stack = params["uuid_stack"]
+
+    staging_path = utils.make_staging_area(sr_path)
+    try:
+        _copy_vdis(sr_path, staging_path, vdi_uuids)
+        imported_vhds = utils.import_vhds(sr_path, staging_path, uuid_stack)
+    finally:
+        utils.cleanup_staging_area(staging_path)
+
+    # Right now, it's easier to return a single string via XenAPI,
+    # so we'll json encode the list of VHDs.
+    return json.dumps(imported_vhds)
+
+
+if __name__ == '__main__':
+    XenAPIPlugin.dispatch({'safe_copy_vdis': safe_copy_vdis})