Improve redfish set-boot-device behaviour

Makes management interface of `redfish` hardware type not changing
current boot frequency if currently set one is the same as the
desired one. The goal is to avoid touching potentially faulty BMC
option whenever possible.

This should hopefully improve interoperability with Redfish BMCs.

Depends-On: https://review.opendev.org/710751
Change-Id: I380cd3aae410e05a4519c3764140ced121bf7fe7
Story: 2007355
Task: 38937

ironic/drivers/modules/redfish/management.py

@@ -126,10 +126,17 @@ class RedfishManagement(base.ManagementInterface):
         """
         system = redfish_utils.get_system(task.node)
 
+        desired_persistence = BOOT_DEVICE_PERSISTENT_MAP_REV[persistent]
+        current_persistence = system.boot.get('enabled')
+
+        # NOTE(etingof): this can be racy, esp if BMC is not RESTful
+        enabled = (desired_persistence
+                   if desired_persistence != current_persistence else None)
+
         try:
             system.set_system_boot_options(
-                BOOT_DEVICE_MAP_REV[device],
-                enabled=BOOT_DEVICE_PERSISTENT_MAP_REV[persistent])
+                BOOT_DEVICE_MAP_REV[device], enabled=enabled)
+
         except sushy.exceptions.SushyError as e:
             error_msg = (_('Redfish set boot device failed for node '
                            '%(node)s. Error: %(error)s') %

ironic/tests/unit/drivers/modules/redfish/test_management.py

@@ -127,6 +127,31 @@ class RedfishManagementTestCase(db_base.DbTestCase):
                 fake_system.set_system_boot_options.reset_mock()
                 mock_get_system.reset_mock()
 
+    @mock.patch.object(redfish_utils, 'get_system', autospec=True)
+    def test_set_boot_device_persistency_no_change(self, mock_get_system):
+        fake_system = mock.Mock()
+        mock_get_system.return_value = fake_system
+        with task_manager.acquire(self.context, self.node.uuid,
+                                  shared=False) as task:
+            expected_values = [
+                (True, sushy.BOOT_SOURCE_ENABLED_CONTINUOUS),
+                (False, sushy.BOOT_SOURCE_ENABLED_ONCE)
+            ]
+
+            for target, expected in expected_values:
+                fake_system.boot.get.return_value = expected
+
+                task.driver.management.set_boot_device(
+                    task, boot_devices.PXE, persistent=target)
+
+                fake_system.set_system_boot_options.assert_called_once_with(
+                    sushy.BOOT_SOURCE_TARGET_PXE, enabled=None)
+                mock_get_system.assert_called_once_with(task.node)
+
+                # Reset mocks
+                fake_system.set_system_boot_options.reset_mock()
+                mock_get_system.reset_mock()
+
     @mock.patch.object(sushy, 'Sushy', autospec=True)
     @mock.patch.object(redfish_utils, 'get_system', autospec=True)
     def test_set_boot_device_fail(self, mock_get_system, mock_sushy):

releasenotes/notes/improve-redfish-set-boot-device-e38e9e9442ab5750.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Makes management interface of ``redfish`` hardware type not changing
+    current boot frequency if currently set is the same as the desired one.
+    The goal is to avoid touching potentially faulty BMC option whenever
+    possible.