NeutronBindNetworkPlugin: fix multi segment mtu

Neutron mtu value for network allocation is taken from share network,
so the share network needs to be updated with the mtu
before the allocation is created.

This prevents the mtu being empty on the first network allocation in
a share network.

Change-Id: I89de02af7d739bbe70f1d893cc2b6ced0157d120
Closes-Bug: #1822099

manila/network/neutron/neutron_network_plugin.py

@@ -566,18 +566,37 @@ class NeutronBindNetworkPlugin(NeutronNetworkPlugin):
 
         In case of dynamic multi segments the segment is determined while
         binding the port. Therefore this method will return for multi segments
-        network without storing network information.
+        network without storing network information (apart from mtu).
 
         Instead, multi segments network will wait until ports are bound and
         then store network information (see allocate_network()).
         """
         if self._is_neutron_multi_segment(share_network):
             # In case of dynamic multi segment the segment is determined while
-            # binding the port
+            # binding the port, only mtu is known and already needed
+            self._save_neutron_network_mtu(context, share_network)
             return
         super(NeutronBindNetworkPlugin, self)._save_neutron_network_data(
             context, share_network)
 
+    def _save_neutron_network_mtu(self, context, share_network):
+        """Store the Neutron network mtu.
+
+        In case of dynamic multi segments only the mtu needs storing before
+        binding the port.
+        """
+        net_info = self.neutron_api.get_network(
+            share_network['neutron_net_id'])
+
+        mtu_dict = {
+            'mtu':  net_info['mtu'],
+        }
+        share_network.update(mtu_dict)
+
+        if self.label != 'admin':
+            self.db.share_network_update(
+                context, share_network['id'], mtu_dict)
+
     def allocate_network(self, context, share_server, share_network=None,
                          **kwargs):
         ports = super(NeutronBindNetworkPlugin, self).allocate_network(

manila/tests/network/neutron/test_neutron_plugin.py

@@ -166,7 +166,7 @@ fake_share_network_multi = {
     'ip_version': None,
     'cidr': 'fake_cidr',
     'gateway': 'fake_gateway',
-    'mtu': fake_neutron_network_multi['mtu'],
+    'mtu': fake_neutron_network_multi['mtu'] - 1,
 }
 
 fake_network_allocation_multi = {
@@ -181,7 +181,7 @@ fake_network_allocation_multi = {
     'ip_version': fake_neutron_subnet['ip_version'],
     'cidr': fake_neutron_subnet['cidr'],
     'gateway': fake_neutron_subnet['gateway_ip'],
-    'mtu': fake_share_network_multi['mtu'],
+    'mtu': fake_neutron_network_multi['mtu'],
 }
 
 fake_binding_profile = {

releasenotes/notes/bug-1822099-fix-multisegment-mtu.yaml-ac2e31c084d8bbb6.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Update share networks with MTU before creating network allocations so that
+    the first allocation in a share network is correct.