From e343452394780b1f555777bc7083912ac68633d3 Mon Sep 17 00:00:00 2001
From: Tim Burke <tim.burke@gmail.com>
Date: Mon, 8 Jan 2018 20:02:50 +0000
Subject: [PATCH] Support existing builders with None _last_part_moves

These were likely written before the first related change, or created
from an existing ring file.

Also, tolerate missing dispersion when rebalancing -- that may not exist
in the builder file.

Change-Id: I26e3b4429c747c23206e4671f7c86543bb182a15
Related-Change: Ib165cf974c865d47c2d9e8f7b3641971d2e9f404
Related-Change: Ie239b958fc7e0547ffda2bebf61546bd4ef3d829
Related-Change: I551fcaf274876861feb12848749590f220842d68
---
 swift/cli/ringbuilder.py          |  3 ++-
 swift/common/ring/builder.py      | 12 ++++++++++--
 test/unit/cli/test_ringbuilder.py |  8 ++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/swift/cli/ringbuilder.py b/swift/cli/ringbuilder.py
index eaddb7b0d3..6498c8d1b5 100644
--- a/swift/cli/ringbuilder.py
+++ b/swift/cli/ringbuilder.py
@@ -945,7 +945,8 @@ swift-ring-builder <builder_file> rebalance [options]
             balance_changed = (
                 abs(last_balance - balance) >= 1 or
                 (last_balance == MAX_BALANCE and balance == MAX_BALANCE))
-            dispersion_changed = abs(last_dispersion - dispersion) >= 1
+            dispersion_changed = last_dispersion is None or (
+                abs(last_dispersion - dispersion) >= 1)
             if balance_changed or dispersion_changed:
                 be_cowardly = False
 
diff --git a/swift/common/ring/builder.py b/swift/common/ring/builder.py
index 717dd753a6..0881bad216 100644
--- a/swift/common/ring/builder.py
+++ b/swift/common/ring/builder.py
@@ -247,7 +247,11 @@ class RingBuilder(object):
             self.version = builder.version
             self._replica2part2dev = builder._replica2part2dev
             self._last_part_moves_epoch = builder._last_part_moves_epoch
-            self._last_part_moves = builder._last_part_moves
+            if builder._last_part_moves is None:
+                self._last_part_moves = array(
+                    'B', itertools.repeat(0, self.parts))
+            else:
+                self._last_part_moves = builder._last_part_moves
             self._last_part_gather_start = builder._last_part_gather_start
             self._remove_devs = builder._remove_devs
             self._id = getattr(builder, '_id', None)
@@ -263,7 +267,11 @@ class RingBuilder(object):
             self.version = builder['version']
             self._replica2part2dev = builder['_replica2part2dev']
             self._last_part_moves_epoch = builder['_last_part_moves_epoch']
-            self._last_part_moves = builder['_last_part_moves']
+            if builder['_last_part_moves'] is None:
+                self._last_part_moves = array(
+                    'B', itertools.repeat(0, self.parts))
+            else:
+                self._last_part_moves = builder['_last_part_moves']
             self._last_part_gather_start = builder['_last_part_gather_start']
             self._dispersion_graph = builder.get('_dispersion_graph', {})
             self.dispersion = builder.get('dispersion')
diff --git a/test/unit/cli/test_ringbuilder.py b/test/unit/cli/test_ringbuilder.py
index 628a9a9a62..7bae4f1b95 100644
--- a/test/unit/cli/test_ringbuilder.py
+++ b/test/unit/cli/test_ringbuilder.py
@@ -2202,6 +2202,14 @@ class TestCommands(unittest.TestCase, RunSwiftRingBuilderMixin):
         argv = ["", backup_file, "write_builder", "24"]
         self.assertIsNone(ringbuilder.main(argv))
 
+        rb = RingBuilder.load(self.tmpfile + '.builder')
+        self.assertIsNotNone(rb._last_part_moves)
+        rb._last_part_moves = None
+        rb.save(self.tmpfile)
+
+        argv = ["", self.tmpfile + '.builder', "rebalance"]
+        self.assertSystemExit(EXIT_WARNING, ringbuilder.main, argv)
+
     def test_warn_at_risk(self):
         # check that warning is generated when rebalance does not achieve
         # satisfactory balance