gist.diff

diff --git a/swift/common/ring/composite_builder.py b/swift/common/ring/composite_builder.py
index 27afc55e0..f73225a9d 100644
--- a/swift/common/ring/composite_builder.py
+++ b/swift/common/ring/composite_builder.py
@@ -55,8 +55,9 @@ def pre_validate_all_builders(builders):
 
     # check regions
     regions_info = {}
-    for i, builder in enumerate(builders):
-        regions_info[i] = set([dev['region'] for dev in builder.devs])
+    for builder in builders:
+        regions_info[builder] = set(
+            [dev['region'] for dev in builder._iter_devs()])
     for first, second in combinations(regions_info.items(), 2):
         inter = first[1] & (second[1])
         if inter:
@@ -68,23 +69,26 @@ def pre_validate_all_builders(builders):
             raise ValueError('Same region found in different rings')
 
 
-def validate_dev_uniqueness(ring_data):
-    """
-    Post-validation for the new zipped rings contains no duplicate devices
+def check_for_dev_uniqueness(builders):
+    builder2devs = {}
 
-    :param ring_data: a RingData insatnce for the zipped ring
-    """
-    # To be simple, just the validate zipped ring here, it is impossible
-    # to report which ring files the incorrect devices appeared in though.
-    ip_port_dev_set = set()
-    for dev in ring_data.devs:
-        if (dev['ip'], dev['port'], dev['device']) in ip_port_dev_set:
-            raise ValueError(
-                'Duplicate ip/port/device combination found '
-                'in the zipped ring file, %s/%s/%s' %
-                (dev['ip'], dev['port'], dev['device']))
-        else:
-            ip_port_dev_set.add((dev['ip'], dev['port'], dev['device']))
+    def check_dev(ip, port, dev):
+        for other_builder, devs in builder2devs.items():
+            if (ip, port, dev) in devs:
+                raise ValueError(
+                    'Duplicate ip/port/device combination %s/%s/%s found '
+                    'in builders %s and %s' %
+                    (ip, port, dev, other_builder.builder_file,
+                     builder.builder_file)
+                )
+
+    for builder in builders:
+        dev_set = set()
+        for dev in builder._iter_devs():
+            dev_params = (dev['ip'], dev['port'], dev['device'])
+            check_dev(*dev_params)
+            dev_set.add(dev_params)
+        builder2devs[builder] = dev_set
 
 
 def composite(ring_builders):
@@ -96,6 +100,7 @@ def composite(ring_builders):
     """
 
     pre_validate_all_builders(ring_builders)
+    check_for_dev_uniqueness(ring_builders)
     zipped_r2p2d = []
     zipped_devs = []
     composite_info = []
@@ -120,5 +125,4 @@ def composite(ring_builders):
 
     rd = RingData(zipped_r2p2d, zipped_devs, ring_builders[0].part_shift,
                   {'composite_info': composite_info})
-    validate_dev_uniqueness(rd)
     return rd
diff --git a/test/unit/common/ring/test_composite_builder.py b/test/unit/common/ring/test_composite_builder.py
index 63a659876..668d05ab1 100644
--- a/test/unit/common/ring/test_composite_builder.py
+++ b/test/unit/common/ring/test_composite_builder.py
@@ -68,9 +68,11 @@ class TestCompositeRingBuilder(unittest.TestCase):
         for region in range(num_builders):
             _, fname = tempfile.mkstemp(dir=self.tmpdir)
             builder = RingBuilder(6, 3, 1, fname)
-            for _ in range(4):
+            for _ in range(5):
                 dev = self.pop_region_device(region)
                 builder.add_dev(dev)
+            # remove last dev to simulate a ring with some history
+            builder.remove_dev(dev['id'])
             builder.rebalance()
             # TODO: make sure if we need to save the builder info as
             #       persistent
@@ -90,11 +92,11 @@ class TestCompositeRingBuilder(unittest.TestCase):
         for builder in builders:
             builder_devs.extend([
                 (dev['ip'], dev['port'], dev['device'])
-                for dev in builder.devs])
+                for dev in builder._iter_devs()])
 
         got_devices = [
             (dev['ip'], dev['port'], dev['device'])
-            for dev in zipped_ring.devs]
+            for dev in zipped_ring.devs if dev]
         self.assertEqual(sorted(builder_devs), sorted(got_devices),
                          "zipped_ring mismatched with part of the rings")
 
@@ -214,8 +216,8 @@ class TestCompositeRingBuilder(unittest.TestCase):
         with self.assertRaises(ValueError) as cm:
             composite(builders)
         self.assertIn(
-            'Duplicate ip/port/device combination found in '
-            'the zipped ring file', cm.exception.message)
+            'Duplicate ip/port/device combination %(ip)s/%(port)s/%(device)s '
+            'found in builders ' % same_device, cm.exception.message)
 
     def test_different_part_power_error(self):
         # create a ring builder