From fe73dfbdc9bc338bddb6bfd09739835b5c48b30c Mon Sep 17 00:00:00 2001
From: "Joshua M. Boniface" <joshua@boniface.me>
Date: Tue, 12 Oct 2021 12:24:03 -0400
Subject: [PATCH] Use current live value for bridge_mtu

This will ensure that upgrading without the bridge_mtu config key set
will keep things as they are.
---
 node-daemon/pvcnoded/util/config.py | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/node-daemon/pvcnoded/util/config.py b/node-daemon/pvcnoded/util/config.py
index 003b0e47..9083f8ea 100644
--- a/node-daemon/pvcnoded/util/config.py
+++ b/node-daemon/pvcnoded/util/config.py
@@ -19,13 +19,17 @@
 #
 ###############################################################################
 
+import daemon_lib.common as common
+
 import os
 import subprocess
 import yaml
+
 from socket import gethostname
 from re import findall
 from psutil import cpu_count
 from ipaddress import ip_address, ip_network
+from json import loads
 
 
 class MalformedConfigurationError(Exception):
@@ -287,13 +291,20 @@ def get_configuration():
             'upstream_mtu':         o_sysnetwork_upstream.get('mtu', None),
             'upstream_dev_ip':      o_sysnetwork_upstream.get('address', None),
             'bridge_dev':           o_sysnetworks.get('bridge_device', None),
-            'bridge_mtu':           o_sysnetworks.get('bridge_mtu', 1500),
+            'bridge_mtu':           o_sysnetworks.get('bridge_mtu', None),
             'enable_sriov':         o_sysnetworks.get('sriov_enable', False),
             'sriov_device':         o_sysnetworks.get('sriov_device', list())
         }
 
         config = {**config, **config_networks}
 
+        if config_networks['bridge_mtu'] is None:
+            # Read the current MTU of bridge_dev and set bridge_mtu to it; avoids weird resets
+            retcode, stdout, stderr = common.run_os_command(f"ip -json link show dev {config_networks['bridge_dev']}")
+            current_bridge_mtu = loads(stdout)[0]['mtu']
+            print(f"Config key bridge_mtu not explicitly set; using live MTU {current_bridge_mtu} from {config_networks['bridge_dev']}")
+            config_networks['bridge_mtu'] = current_bridge_mtu
+
         for network_type in ['cluster', 'storage', 'upstream']:
             result, msg = validate_floating_ip(config, network_type)
             if not result: