Add ability to manage fallback network config on PhotonOS (#941)

Currently cloud-init generates fallback network config on various
scenarios.

For example:
1. When no DS found
2. There is no 'network' info given in DS metadata.
3. If a DS gives a network config once and upon reboot if DS doesn't
   give any network info, previously set network data will be
   overridden.

A newly introduced key in cloud.cfg.tmpl can be used to control this
behavior on PhotonOS.

Also, if OS comes with a set of default network files(configs), like in
PhotonOS, cloud-init should not overwrite them by default.

This change also includes some nitpicking changes of reorganizing few
config variables.

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/tests/unittests/test_distros/test_photon.py b/tests/unittests/test_distros/test_photon.py
new file mode 100644
index 00000000..775f37ac
--- /dev/null
+++ b/tests/unittests/test_distros/test_photon.py
@@ -0,0 +1,51 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+from . import _get_distro
+from cloudinit import util
+from cloudinit.tests.helpers import mock
+from cloudinit.tests.helpers import CiTestCase
+
+SYSTEM_INFO = {
+    'paths': {
+        'cloud_dir': '/var/lib/cloud/',
+        'templates_dir': '/etc/cloud/templates/',
+    },
+    'network': {'renderers': 'networkd'},
+}
+
+
+class TestPhoton(CiTestCase):
+    with_logs = True
+    distro = _get_distro('photon', SYSTEM_INFO)
+    expected_log_line = 'Rely on PhotonOS default network config'
+
+    def test_network_renderer(self):
+        self.assertEqual(self.distro._cfg['network']['renderers'], 'networkd')
+
+    def test_get_distro(self):
+        self.assertEqual(self.distro.osfamily, 'photon')
+
+    def test_write_hostname(self):
+        hostname = 'myhostname'
+        hostfile = self.tmp_path('hostfile')
+        self.distro._write_hostname(hostname, hostfile)
+        self.assertEqual(hostname + '\n', util.load_file(hostfile))
+
+    @mock.patch('cloudinit.net.generate_fallback_config')
+    def test_fallback_netcfg(self, m_fallback_cfg):
+
+        key = 'disable_fallback_netcfg'
+        # Don't use fallback if no setting given
+        self.logs.truncate(0)
+        assert(self.distro.generate_fallback_config() is None)
+        self.assertIn(self.expected_log_line, self.logs.getvalue())
+
+        self.logs.truncate(0)
+        self.distro._cfg[key] = True
+        assert(self.distro.generate_fallback_config() is None)
+        self.assertIn(self.expected_log_line, self.logs.getvalue())
+
+        self.logs.truncate(0)
+        self.distro._cfg[key] = False
+        assert(self.distro.generate_fallback_config() is not None)
+        self.assertNotIn(self.expected_log_line, self.logs.getvalue())