Add missing exception

Change Idd49b0c70caedfcd42420ffa2ac926a6087d406e added support for
discovery of PMEM devices by the libvirt driver. Some error handling
code in this was expected to raise a 'GetPMEMNamespacesFailed'
exception, however, a typo meant the exception was actually called
'GetPMEMNamespaceFailed' (singular). This exception was later removed in
change I6fd027fb51823b8a8a24ed7b864a2191c4e8e8c0 because it had no
references.

Re-introduce the exception, this time with the correct name, and add
some unit tests to prevent us regressing.

Change-Id: I3b597a46314a1b29a952fc0f7a9c4537341e37b8
Signed-off-by: Stephen Finucane <[email protected]>
Closes-Bug: #1904446
(cherry picked from commit 160ed6f)

nova/exception.py

@@ -2281,6 +2281,10 @@ class PMEMNamespaceConfigInvalid(NovaException):
                 "please check your conf file. ")
 
 
+class GetPMEMNamespacesFailed(NovaException):
+    msg_fmt = _("Get PMEM namespaces on host failed: %(reason)s.")
+
+
 class VPMEMCleanupFailed(NovaException):
     msg_fmt = _("Failed to clean up the vpmem backend device %(dev)s: "
                 "%(error)s")

nova/tests/unit/virt/libvirt/test_driver.py

@@ -27549,6 +27549,15 @@ def test_vpmems_duplicated_config(self, mock_get):
         self.assertRaises(exception.PMEMNamespaceConfigInvalid,
                           drvr._discover_vpmems, vpmem_conf)
 
+    @mock.patch('nova.privsep.libvirt.get_pmem_namespaces')
+    def test_get_vpmems_on_host__exception(self, mock_get_ns):
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
+        mock_get_ns.side_effect = Exception('foo')
+
+        self.assertRaises(
+            exception.GetPMEMNamespacesFailed,
+            drvr._get_vpmems_on_host)
+
     @mock.patch('nova.virt.hardware.get_vpmems')
     def test_get_ordered_vpmems(self, mock_labels):
         # get orgered vpmems based on flavor extra_specs