volume/driver: implement basic snapshot/clone

added basic support for snapshot/clone to VolumeDriver.
The implementation is not effective, but works. The effective
implementation should be done by drived driver class.

Authors

@@ -28,6 +28,7 @@ Gabe Westmaas <gabe.westmaas@rackspace.com>
 Hisaharu Ishii <ishii.hisaharu@lab.ntt.co.jp>
 Hisaki Ohara <hisaki.ohara@intel.com>
 Ilya Alekseyev <ialekseev@griddynamics.com>
+Isaku Yamahata <yamahata@valinux.co.jp>
 Jason Koelker <jason@koelker.net>
 Jay Pipes <jaypipes@gmail.com>
 Jesse Andrews <anotherjesse@gmail.com>

nova/exception.py

@@ -79,6 +79,12 @@ class VolumeNotFound(NotFound):
         super(VolumeNotFound, self).__init__(message)
 
 
+class VolumeIsBusy(Error):
+    def __init__(self, message, volume_id):
+        self.volume_id = volume_id
+        super(Error, self).__init__(message)
+
+
 class SnapshotNotFound(NotFound):
     def __init__(self, message, snapshot_id):
         self.snapshot_id = snapshot_id

nova/volume/driver.py

@@ -113,13 +113,21 @@ class VolumeDriver(object):
         # TODO(ja): reclaiming space should be done lazy and low priority
         self._copy_volume('/dev/zero', self.local_path(volume), size_in_g)
         self._try_execute('sudo', 'lvremove', '-f', "%s/%s" %
-                          (FLAGS.volume_group, volume['name']))
+                          (FLAGS.volume_group,
+                           self._escape_snapshot(volume['name'])))
         
     def _sizestr(self, size_in_g):
         if int(size_in_g) == 0:
             return '100M'
         return '%sG' % size_in_g
 
+    # Linux LVM reserves name that starts with snapshot, so that
+    # such volume name can't be created. Mangle it.
+    def _escape_snapshot(self, snapshot_name):
+        if not snapshot_name.startswith('snapshot'):
+            return snapshot_name
+        return '_' + snapshot_name
+
     def create_volume(self, volume):
         """Creates a logical volume. Can optionally return a Dictionary of
         changes to the volume object to be persisted."""
@@ -127,27 +135,51 @@ class VolumeDriver(object):
 
     def create_volume_from_snapshot(self, volume, snapshot):
         """Creates a volume from a snapshot."""
-        raise NotImplementedError()
+        self._create_volume(volume['name'], self._sizestr(volume['size']))
+        self._copy_volume(self.local_path(snapshot), self.local_path(volume),
+                          snapshot['volume_size'])
 
     def delete_volume(self, volume):
         """Deletes a logical volume."""
         if self._volume_not_present(volume['name']):
             # If the volume isn't present, then don't attempt to delete
             return True
+
+        # TODO(yamahata): lvm can't delete origin volume only without
+        # deleting derived snapshots. Can we do something fancy?
+        out, err = self._execute('sudo', 'lvdisplay', '--noheading',
+                                 '-C', '-o', 'Attr',
+                                 '%s/%s' % (FLAGS.volume_group,
+                                            volume['name']))
+        out = out.strip()
+        if (out[0] == 'o') or (out[0] == 'O'):
+            raise exception.VolumeIsBusy(
+                _('deleting volume %s that has snapshot'), volume['name'])
+                
         self._delete_volume(volume, volume['size'])
 
     def create_snapshot(self, snapshot):
         """Creates a snapshot."""
-        raise NotImplementedError()
+        orig_lv_name = "%s/%s" % (FLAGS.volume_group, snapshot['volume_name'])
+        self._try_execute('sudo', 'lvcreate', '-L',
+                          self._sizestr(snapshot['volume_size']),
+                          '--name', self._escape_snapshot(snapshot['name']),
+                          '--snapshot', orig_lv_name)
 
     def delete_snapshot(self, snapshot):
         """Deletes a snapshot."""
-        raise NotImplementedError()
+        if self._volume_not_present(self._escape_snapshot(snapshot['name'])):
+            # If the snapshot isn't present, then don't attempt to delete
+            return True
+
+        # TODO(yamahata): zeroing out the whole snapshot triggers COW.
+        # it's quite slow.
+        self._delete_volume(snapshot, snapshot['volume_size'])
 
     def local_path(self, volume):
         # NOTE(vish): stops deprecation warning
         escaped_group = FLAGS.volume_group.replace('-', '--')
-        escaped_name = volume['name'].replace('-', '--')
+        escaped_name = self._escape_snapshot(volume['name']).replace('-', '--')
         return "/dev/mapper/%s-%s" % (escaped_group, escaped_name)
 
     def ensure_export(self, context, volume):

nova/volume/manager.py

@@ -147,6 +147,12 @@ class VolumeManager(manager.SchedulerDependentManager):
             self.driver.remove_export(context, volume_ref)
             LOG.debug(_("volume %s: deleting"), volume_ref['name'])
             self.driver.delete_volume(volume_ref)
+        except exception.VolumeIsBusy, e:
+            LOG.debug(_("volume %s: volume is busy"), volume_ref['name'])
+            self.driver.ensure_export(context, volume_ref)
+            self.db.volume_update(context, volume_ref['id'],
+                                  {'status': 'available'})
+            return True
         except Exception:
             self.db.volume_update(context,
                                   volume_ref['id'],