Add "install hotplug" module (SC-476) (#1069)

This commit removes automatically installing udev rules for hotplug
and adds a module to install them instead.

Automatically including the udev rules and checking if hotplug was
enabled consumed too many resources in certain circumstances. Moving the
rules to a module ensures we don't spend extra extra cycles on hotplug
if hotplug functionality isn't desired.

LP: #1946003

3 files changed, 123 insertions, 8 deletions

diff --git a/tests/unittests/cmd/devel/test_hotplug_hook.py b/tests/unittests/cmd/devel/test_hotplug_hook.py
index 63d2490e..e1c64e2f 100644
--- a/tests/unittests/cmd/devel/test_hotplug_hook.py
+++ b/tests/unittests/cmd/devel/test_hotplug_hook.py
@@ -30,6 +30,11 @@ def mocks():
         return_value=FAKE_MAC
     )
 
+    update_event_enabled = mock.patch(
+        'cloudinit.stages.update_event_enabled',
+        return_value=True,
+    )
+
     m_network_state = mock.MagicMock(spec=NetworkState)
     parse_net = mock.patch(
         'cloudinit.cmd.devel.hotplug_hook.parse_net_config_data',
@@ -45,6 +50,7 @@ def mocks():
     sleep = mock.patch('time.sleep')
 
     read_sys_net.start()
+    update_event_enabled.start()
     parse_net.start()
     select_activator.start()
     m_sleep = sleep.start()
@@ -57,6 +63,7 @@ def mocks():
     )
 
     read_sys_net.stop()
+    update_event_enabled.stop()
     parse_net.stop()
     select_activator.stop()
     sleep.stop()
@@ -122,13 +129,16 @@ class TestHotplug:
 
     def test_update_event_disabled(self, mocks, caplog):
         init = mocks.m_init
-        init.update_event_enabled.return_value = False
-        handle_hotplug(
-            hotplug_init=init,
-            devpath='/dev/fake',
-            udevaction='remove',
-            subsystem='net'
-        )
+        with mock.patch(
+            'cloudinit.stages.update_event_enabled',
+            return_value=False
+        ):
+            handle_hotplug(
+                hotplug_init=init,
+                devpath='/dev/fake',
+                udevaction='remove',
+                subsystem='net'
+            )
         assert 'hotplug not enabled for event of type' in caplog.text
         init.datasource.update_metadata_if_supported.assert_not_called()
         mocks.m_activator.bring_up_interface.assert_not_called()
diff --git a/tests/unittests/test_handler/test_handler_install_hotplug.py b/tests/unittests/test_handler/test_handler_install_hotplug.py
new file mode 100644
index 00000000..19b0cc41
--- /dev/null
+++ b/tests/unittests/test_handler/test_handler_install_hotplug.py
@@ -0,0 +1,104 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+from collections import namedtuple
+from unittest import mock
+
+import pytest
+
+from cloudinit.config.cc_install_hotplug import (
+    handle,
+    HOTPLUG_UDEV_PATH,
+    HOTPLUG_UDEV_RULES,
+)
+from cloudinit.event import EventScope, EventType
+
+
+@pytest.yield_fixture()
+def mocks():
+    m_update_enabled = mock.patch('cloudinit.stages.update_event_enabled')
+    m_write = mock.patch('cloudinit.util.write_file', autospec=True)
+    m_del = mock.patch('cloudinit.util.del_file', autospec=True)
+    m_subp = mock.patch('cloudinit.subp.subp')
+    m_which = mock.patch('cloudinit.subp.which', return_value=None)
+    m_path_exists = mock.patch('os.path.exists', return_value=False)
+
+    yield namedtuple(
+        'Mocks',
+        'm_update_enabled m_write m_del m_subp m_which m_path_exists'
+    )(
+        m_update_enabled.start(), m_write.start(), m_del.start(),
+        m_subp.start(), m_which.start(), m_path_exists.start()
+    )
+
+    m_update_enabled.stop()
+    m_write.stop()
+    m_del.stop()
+    m_subp.stop()
+    m_which.stop()
+    m_path_exists.stop()
+
+
+class TestInstallHotplug:
+    def test_rules_installed_when_supported_and_enabled(self, mocks):
+        mocks.m_which.return_value = 'udevadm'
+        mocks.m_update_enabled.return_value = True
+        m_cloud = mock.MagicMock()
+        m_cloud.datasource.get_supported_events.return_value = {
+            EventScope.NETWORK: {EventType.HOTPLUG}
+        }
+
+        handle(None, {}, m_cloud, mock.Mock(), None)
+        mocks.m_write.assert_called_once_with(
+            filename=HOTPLUG_UDEV_PATH,
+            content=HOTPLUG_UDEV_RULES,
+        )
+        assert mocks.m_subp.call_args_list == [mock.call([
+            'udevadm', 'control', '--reload-rules',
+        ])]
+        assert mocks.m_del.call_args_list == []
+
+    def test_rules_not_installed_when_unsupported(self, mocks):
+        mocks.m_update_enabled.return_value = True
+        m_cloud = mock.MagicMock()
+        m_cloud.datasource.get_supported_events.return_value = {}
+
+        handle(None, {}, m_cloud, mock.Mock(), None)
+        assert mocks.m_write.call_args_list == []
+        assert mocks.m_del.call_args_list == []
+        assert mocks.m_subp.call_args_list == []
+
+    def test_rules_not_installed_when_disabled(self, mocks):
+        mocks.m_update_enabled.return_value = False
+        m_cloud = mock.MagicMock()
+        m_cloud.datasource.get_supported_events.return_value = {
+            EventScope.NETWORK: {EventType.HOTPLUG}
+        }
+
+        handle(None, {}, m_cloud, mock.Mock(), None)
+        assert mocks.m_write.call_args_list == []
+        assert mocks.m_del.call_args_list == []
+        assert mocks.m_subp.call_args_list == []
+
+    def test_rules_uninstalled_when_disabled(self, mocks):
+        mocks.m_path_exists.return_value = True
+        mocks.m_update_enabled.return_value = False
+        m_cloud = mock.MagicMock()
+        m_cloud.datasource.get_supported_events.return_value = {}
+
+        handle(None, {}, m_cloud, mock.Mock(), None)
+        mocks.m_del.assert_called_with(HOTPLUG_UDEV_PATH)
+        assert mocks.m_subp.call_args_list == [mock.call([
+            'udevadm', 'control', '--reload-rules',
+        ])]
+        assert mocks.m_write.call_args_list == []
+
+    def test_rules_not_installed_when_no_udevadm(self, mocks):
+        mocks.m_update_enabled.return_value = True
+        m_cloud = mock.MagicMock()
+        m_cloud.datasource.get_supported_events.return_value = {
+            EventScope.NETWORK: {EventType.HOTPLUG}
+        }
+
+        handle(None, {}, m_cloud, mock.Mock(), None)
+        assert mocks.m_del.call_args_list == []
+        assert mocks.m_write.call_args_list == []
+        assert mocks.m_subp.call_args_list == []
diff --git a/tests/unittests/test_handler/test_schema.py b/tests/unittests/test_handler/test_schema.py
index 59f58f7c..1dae223d 100644
--- a/tests/unittests/test_handler/test_schema.py
+++ b/tests/unittests/test_handler/test_schema.py
@@ -36,7 +36,8 @@ class GetSchemaTest(CiTestCase):
                 'cc_write_files',
                 'cc_write_files_deferred',
                 'cc_zypper_add_repo',
-                'cc_chef'
+                'cc_chef',
+                'cc_install_hotplug',
             ],
             [subschema['id'] for subschema in schema['allOf']])
         self.assertEqual('cloud-config-schema', schema['id'])