net: support network-config:disabled on the kernel commandline (#232)

Allow disabling cloud-init's network configuration via a plain-text kernel cmdline

Cloud-init docs indicate that users can disable cloud-init networking via kernel
command line parameter 'network-config=<YAML>'.  This does not work unless 
the <YAML> payload base64 encoded.  Document the base64 encoding
requirement and add a plain-text value for disabling cloud-init network config:

    network-config=disabled

Also:
 - Log an error and ignore any plain-text network-config payloads that are
   not specifically 'network-config=disabled'.
 - Log a warning if network-config kernel param is invalid yaml but do not
   raise an exception, allowing boot to continue and use fallback networking.

LP: #1862702

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/unittests/test_net.py b/tests/unittests/test_net.py
index bedd05fe..e03857c4 100644
--- a/tests/unittests/test_net.py
+++ b/tests/unittests/test_net.py
@@ -4017,6 +4017,8 @@ class TestEniNetworkStateToEni(CiTestCase):
 
 
 class TestCmdlineConfigParsing(CiTestCase):
+    with_logs = True
+
     simple_cfg = {
         'config': [{"type": "physical", "name": "eth0",
                     "mac_address": "c0:d6:9f:2c:e8:80",
@@ -4066,6 +4068,21 @@ class TestCmdlineConfigParsing(CiTestCase):
         found = cmdline.read_kernel_cmdline_config(cmdline=raw_cmdline)
         self.assertEqual(found, self.simple_cfg)
 
+    def test_cmdline_with_net_config_disabled(self):
+        raw_cmdline = 'ro network-config=disabled root=foo'
+        found = cmdline.read_kernel_cmdline_config(cmdline=raw_cmdline)
+        self.assertEqual(found, {'config': 'disabled'})
+
+    def test_cmdline_with_net_config_unencoded_logs_error(self):
+        """network-config cannot be unencoded besides 'disabled'."""
+        raw_cmdline = 'ro network-config={config:disabled} root=foo'
+        found = cmdline.read_kernel_cmdline_config(cmdline=raw_cmdline)
+        self.assertIsNone(found)
+        expected_log = (
+            'ERROR: Expected base64 encoded kernel commandline parameter'
+            ' network-config. Ignoring network-config={config:disabled}.')
+        self.assertIn(expected_log, self.logs.getvalue())
+
     def test_cmdline_with_b64_gz(self):
         data = _gzip_data(json.dumps(self.simple_cfg).encode())
         encoded_text = base64.b64encode(data).decode()