volume/driver: implement basic snapshot

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

3 files changed, 43 insertions, 4 deletions

diff --git a/nova/exception.py b/nova/exception.py
index 39620ccc1..bd04435ed 100644
--- a/nova/exception.py
+++ b/nova/exception.py
@@ -271,6 +271,10 @@ class SnapshotNotFound(NotFound):
     message = _("Snapshot %(snapshot_id)s could not be found.")
 
 
+class VolumeIsBusy(Error):
+    message = _("deleting volume %(volume_name)s that has snapshot")
+
+
 class ExportDeviceNotFoundForVolume(NotFound):
     message = _("No export device found for volume %(volume_id)s.")
 
diff --git a/nova/volume/driver.py b/nova/volume/driver.py
index ec7be37bf..a6cf2cb46 100644
--- a/nova/volume/driver.py
+++ b/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."""
@@ -130,20 +138,41 @@ class VolumeDriver(object):
         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(volume_name=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):
diff --git a/nova/volume/manager.py b/nova/volume/manager.py
index 87fd3bf17..fd889633d 100644
--- a/nova/volume/manager.py
+++ b/nova/volume/manager.py
@@ -142,6 +142,12 @@ 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'],