diff --git a/nova/privsep/utils.py b/nova/privsep/utils.py
index 6ba9c4c89773..2b9d9703acdd 100644
--- a/nova/privsep/utils.py
+++ b/nova/privsep/utils.py
@@ -27,6 +27,7 @@ import os
 from oslo_log import log as logging
 from oslo_utils import excutils
 
+from nova import utils as nova_utils
 
 LOG = logging.getLogger(__name__)
 
@@ -37,7 +38,9 @@ def supports_direct_io(dirpath):
         LOG.debug("This python runtime does not support direct I/O")
         return False
 
-    testfile = os.path.join(dirpath, ".directio.test")
+    file_name = "%s.%s" % (".directio.test",
+                           nova_utils.generate_random_string())
+    testfile = os.path.join(dirpath, file_name)
 
     hasDirectIO = True
     fd = None
diff --git a/nova/tests/functional/test_servers.py b/nova/tests/functional/test_servers.py
index 3f962722673e..d1af06c171c1 100644
--- a/nova/tests/functional/test_servers.py
+++ b/nova/tests/functional/test_servers.py
@@ -632,6 +632,8 @@ class ServersTest(ServersTestBase):
         self.assertIn('reservation_id', response)
         reservation_id = response['reservation_id']
         self.assertNotIn(reservation_id, ['', None])
+        # Assert that the reservation_id itself has the expected format
+        self.assertRegex(reservation_id, 'r-[0-9a-zA-Z]{8}')
 
         # Create 1 more server, which should not return a reservation_id
         server = self._build_minimal_create_server_request()
diff --git a/nova/tests/unit/privsep/test_utils.py b/nova/tests/unit/privsep/test_utils.py
index 6d87a643641c..cdb64331fa31 100644
--- a/nova/tests/unit/privsep/test_utils.py
+++ b/nova/tests/unit/privsep/test_utils.py
@@ -36,21 +36,25 @@ class SupportDirectIOTestCase(test.NoDBTestCase):
         self.einval.errno = errno.EINVAL
         self.enoent = OSError()
         self.enoent.errno = errno.ENOENT
-        self.test_path = os.path.join('.', '.directio.test')
+        self.test_path = os.path.join('.', '.directio.test.abc123')
         self.io_flags = os.O_CREAT | os.O_WRONLY | os.O_DIRECT
 
         open_patcher = mock.patch('os.open')
         write_patcher = mock.patch('os.write')
         close_patcher = mock.patch('os.close')
         unlink_patcher = mock.patch('os.unlink')
+        random_string_patcher = mock.patch('nova.utils.generate_random_string',
+                                           return_value='abc123')
         self.addCleanup(open_patcher.stop)
         self.addCleanup(write_patcher.stop)
         self.addCleanup(close_patcher.stop)
         self.addCleanup(unlink_patcher.stop)
+        self.addCleanup(random_string_patcher.stop)
         self.mock_open = open_patcher.start()
         self.mock_write = write_patcher.start()
         self.mock_close = close_patcher.start()
         self.mock_unlink = unlink_patcher.start()
+        random_string_patcher.start()
 
     def test_supports_direct_io(self):
         self.mock_open.return_value = 3
diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index f9a1ac31731a..6c1bae617830 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -2435,6 +2435,8 @@ class LibvirtConnTestCase(test.NoDBTestCase,
             self.assertEqual(0, len(cfg.cputune.vcpupin))
             self.assertIsNone(cfg.cpu.numa)
 
+    @mock.patch('nova.privsep.utils.supports_direct_io',
+                new=mock.Mock(return_value=True))
     @mock.patch.object(
         host.Host, "is_cpu_control_policy_capable", return_value=True)
     def test_get_guest_config_numa_host_instance_no_fit(self, is_able):
@@ -2686,6 +2688,8 @@ class LibvirtConnTestCase(test.NoDBTestCase,
             self.assertEqual(0, len(cfg.cputune.vcpupin))
             self.assertIsNone(cfg.cpu.numa)
 
+    @mock.patch('nova.privsep.utils.supports_direct_io',
+                new=mock.Mock(return_value=True))
     @mock.patch.object(
         host.Host, "is_cpu_control_policy_capable", return_value=True)
     def test_get_guest_config_numa_host_instance_2pci_no_fit(self, is_able):
diff --git a/nova/utils.py b/nova/utils.py
index a890d3ea67a4..a9d29a4f36ee 100644
--- a/nova/utils.py
+++ b/nova/utils.py
@@ -244,9 +244,13 @@ def ssh_execute(dest, *cmd, **kwargs):
 
 
 def generate_uid(topic, size=8):
+    random_string = generate_random_string(size)
+    return '%s-%s' % (topic, random_string)
+
+
+def generate_random_string(size=8):
     characters = '01234567890abcdefghijklmnopqrstuvwxyz'
-    choices = [random.choice(characters) for _x in range(size)]
-    return '%s-%s' % (topic, ''.join(choices))
+    return ''.join([random.choice(characters) for _x in range(size)])
 
 
 # Default symbols to use for passwords. Avoids visually confusing characters.