Handle non-updatable openstack subnet details

Some things cannot be updated via the API, so check for those and fail
if the user is wanting to update them. Also don't try to update ipv6
stuff, as that doesn't work and will cause a traceback.

lib/ansible/modules/cloud/openstack/os_subnet.py

@@ -144,9 +144,38 @@ EXAMPLES = '''
     ipv6_address_mode: dhcpv6-stateless
 '''
 
+def _can_update(subnet, module, cloud):
+    """Check for differences in non-updatable values"""
+    network_name = module.params['network_name']
+    cidr = module.params['cidr']
+    ip_version = int(module.params['ip_version'])
+    ipv6_ra_mode = module.params['ipv6_ra_mode']
+    ipv6_a_mode = module.params['ipv6_address_mode']
+
+    if network_name:
+        network = cloud.get_network(network_name)
+        if network:
+            netid = network['id']
+        else:
+            module.fail_json(msg='No network found for %s' % network_name)
+        if netid != subnet['network_id']:
+                module.fail_json(msg='Cannot update network_name in existing \
+                                      subnet')
+    if ip_version and subnet['ip_version'] != ip_version:
+        module.fail_json(msg='Cannot update ip_version in existing subnet')
+    if ipv6_ra_mode and subnet.get('ipv6_ra_mode', None) != ip_version:
+        module.fail_json(msg='Cannot update ipv6_ra_mode in existing subnet')
+    if ipv6_a_mode and subnet.get('ipv6_address_mode', None) != ipv6_a_mode:
+        module.fail_json(msg='Cannot update ipv6_address_mode in existing \
+                              subnet')
 
-def _needs_update(subnet, module):
+def _needs_update(subnet, module, cloud):
     """Check for differences in the updatable values."""
+
+    # First check if we are trying to update something we're not allowed to
+    _can_update(subnet, module, cloud)
+
+    # now check for the things we are allowed to update
     enable_dhcp = module.params['enable_dhcp']
     subnet_name = module.params['name']
     pool_start = module.params['allocation_pool_start']
@@ -176,12 +205,12 @@ def _needs_update(subnet, module):
     return False
 
 
-def _system_state_change(module, subnet):
+def _system_state_change(module, subnet, cloud):
     state = module.params['state']
     if state == 'present':
         if not subnet:
             return True
-        return _needs_update(subnet, module)
+        return _needs_update(subnet, module, cloud)
     if state == 'absent' and subnet:
         return True
     return False
@@ -245,7 +274,8 @@ def main():
         subnet = cloud.get_subnet(subnet_name)
 
         if module.check_mode:
-            module.exit_json(changed=_system_state_change(module, subnet))
+            module.exit_json(changed=_system_state_change(module, subnet,
+                                                          cloud))
 
         if state == 'present':
             if not subnet:
@@ -261,16 +291,14 @@ def main():
                                              ipv6_address_mode=ipv6_a_mode)
                 changed = True
             else:
-                if _needs_update(subnet, module):
+                if _needs_update(subnet, module, cloud):
                     cloud.update_subnet(subnet['id'],
                                         subnet_name=subnet_name,
                                         enable_dhcp=enable_dhcp,
                                         gateway_ip=gateway_ip,
                                         dns_nameservers=dns,
                                         allocation_pools=pool,
-                                        host_routes=host_routes,
-                                        ipv6_ra_mode=ipv6_ra_mode,
-                                        ipv6_address_mode=ipv6_a_mode)
+                                        host_routes=host_routes)
                     changed = True
                 else:
                     changed = False