netplan: fix mtu if provided by network config for all rendered types

When network configuration for any interface defines maximum transmission
values (MTU) the netplan, eni and sysconfig renders will take into account
any device-level, or subnet-level mtu values.

When network configuration has conflicting device-level and ipv4 subnet
mtu values, the subnet-specific value is honored and a warning will be
logged about any ignored device-level setting.

LP: #1774666

1 files changed, 14 insertions, 8 deletions

diff --git a/cloudinit/net/netplan.py b/cloudinit/net/netplan.py
index 63443484..40143634 100644
--- a/cloudinit/net/netplan.py
+++ b/cloudinit/net/netplan.py
@@ -34,7 +34,7 @@ def _get_params_dict_by_match(config, match):
                 if key.startswith(match))
 
 
-def _extract_addresses(config, entry):
+def _extract_addresses(config, entry, ifname):
     """This method parse a cloudinit.net.network_state dictionary (config) and
        maps netstate keys/values into a dictionary (entry) to represent
        netplan yaml.
@@ -124,6 +124,15 @@ def _extract_addresses(config, entry):
 
             addresses.append(addr)
 
+    if 'mtu' in config:
+        entry_mtu = entry.get('mtu')
+        if entry_mtu and config['mtu'] != entry_mtu:
+            LOG.warning(
+                "Network config: ignoring %s device-level mtu:%s because"
+                " ipv4 subnet-level mtu:%s provided.",
+                ifname, config['mtu'], entry_mtu)
+        else:
+            entry['mtu'] = config['mtu']
     if len(addresses) > 0:
         entry.update({'addresses': addresses})
     if len(routes) > 0:
@@ -262,10 +271,7 @@ class Renderer(renderer.Renderer):
                     else:
                         del eth['match']
                         del eth['set-name']
-                if 'mtu' in ifcfg:
-                    eth['mtu'] = ifcfg.get('mtu')
-
-                _extract_addresses(ifcfg, eth)
+                _extract_addresses(ifcfg, eth, ifname)
                 ethernets.update({ifname: eth})
 
             elif if_type == 'bond':
@@ -288,7 +294,7 @@ class Renderer(renderer.Renderer):
                 slave_interfaces = ifcfg.get('bond-slaves')
                 if slave_interfaces == 'none':
                     _extract_bond_slaves_by_name(interfaces, bond, ifname)
-                _extract_addresses(ifcfg, bond)
+                _extract_addresses(ifcfg, bond, ifname)
                 bonds.update({ifname: bond})
 
             elif if_type == 'bridge':
@@ -321,7 +327,7 @@ class Renderer(renderer.Renderer):
 
                 if len(br_config) > 0:
                     bridge.update({'parameters': br_config})
-                _extract_addresses(ifcfg, bridge)
+                _extract_addresses(ifcfg, bridge, ifname)
                 bridges.update({ifname: bridge})
 
             elif if_type == 'vlan':
@@ -333,7 +339,7 @@ class Renderer(renderer.Renderer):
                 macaddr = ifcfg.get('mac_address', None)
                 if macaddr is not None:
                     vlan['macaddress'] = macaddr.lower()
-                _extract_addresses(ifcfg, vlan)
+                _extract_addresses(ifcfg, vlan, ifname)
                 vlans.update({ifname: vlan})
 
         # inject global nameserver values under each all interface which