fix(final_message): do not warn on datasourcenone when single ds

Avoid warning level log "Used fallback datasource" when base
configuration defines `datasource_list: [ None ]`.

Using DataSourceNone in this case is desired behavior.

Also drop unused is_disconnected property from DataSource
which was only used by DataSourceNone in cc_final_message.

Instead compare based on dsname property.

Fixes: GH-5192

cloudinit/config/cc_final_message.py

@@ -110,5 +110,10 @@ def handle(name: str, cfg: Config, cloud: Cloud, args: list) -> None:
     except Exception:
         util.logexc(LOG, "Failed to write boot finished file %s", boot_fin_fn)
 
-    if cloud.datasource.is_disconnected:
-        LOG.warning("Used fallback datasource")
+    if cloud.datasource.dsname == "None":
+        if cloud.datasource.sys_cfg.get("datasource_list") == ["None"]:
+            # No warn on expected behavior when datasource_list: [ None ]
+            log_func = LOG.debug
+        else:
+            log_func = LOG.warning
+        log_func("Used fallback datasource")

cloudinit/sources/DataSourceNone.py

@@ -32,10 +32,6 @@ def _get_subplatform(self):
     def get_instance_id(self):
         return "iid-datasource-none"
 
-    @property
-    def is_disconnected(self):
-        return True
-
 
 # Used to match classes to dependencies
 datasources = [

cloudinit/sources/__init__.py

@@ -726,10 +726,6 @@ def _filter_xdata(self, processed_ud):
             new_ud = f.apply(new_ud)
         return new_ud
 
-    @property
-    def is_disconnected(self):
-        return False
-
     def get_userdata_raw(self):
         return self.userdata_raw
 

tests/unittests/config/test_cc_final_message.py

@@ -1,9 +1,12 @@
 # This file is part of cloud-init. See LICENSE file for license information.
+from logging import DEBUG, WARNING
+from pathlib import Path
 from unittest import mock
 
 import pytest
 
 from cloudinit.config.cc_final_message import handle
+from tests.unittests.util import get_cloud
 
 
 class TestHandle:
@@ -24,17 +27,15 @@ def test_boot_finished_written(
         file_is_written,
         expected_log_substring,
         caplog,
+        paths,
         tmpdir,
     ):
-        instance_dir = tmpdir.join("var/lib/cloud/instance")
+        instance_dir = Path(paths.get_ipath_cur())
         if instance_dir_exists:
-            instance_dir.ensure_dir()
-        boot_finished = instance_dir.join("boot-finished")
-
-        m_cloud = mock.Mock(
-            paths=mock.Mock(boot_finished=boot_finished.strpath)
-        )
+            instance_dir.mkdir()
+        boot_finished = instance_dir / "boot-finished"
 
+        m_cloud = get_cloud(paths=paths)
         handle(None, {}, m_cloud, [])
 
         # We should not change the status of the instance directory
@@ -43,3 +44,36 @@ def test_boot_finished_written(
 
         if expected_log_substring:
             assert expected_log_substring in caplog.text
+
+    @pytest.mark.parametrize(
+        "dsname,datasource_list,expected_log,log_level",
+        [
+            ("None", ["None"], "Used fallback datasource", DEBUG),
+            ("None", ["LXD", "None"], "Used fallback datasource", WARNING),
+            ("LXD", ["LXD", "None"], None, DEBUG),
+        ],
+    )
+    def test_only_warn_when_datasourcenone_is_fallback_in_datasource_list(
+        self,
+        dsname,
+        datasource_list,
+        expected_log,
+        log_level,
+        caplog,
+        paths,
+    ):
+        """Only warn when None is a fallback in multi-item datasource_list.
+
+        It is not a warning when datasource_list: [ None ] is configured.
+        """
+        m_cloud = get_cloud(paths=paths)
+        m_cloud.datasource.dsname = dsname
+        Path(paths.get_ipath_cur()).mkdir()
+        with caplog.at_level(log_level):
+            handle(None, {}, m_cloud, [])
+
+        # We should not change the status of the instance directory
+        if expected_log:
+            assert expected_log in caplog.text
+        else:
+            assert "Used fallback datasource" not in caplog.text