lib: nlcache: merge existing MTU into new netlink object before caching

Signed-off-by: Julien Fortin <jfortin@nvidia.com>

diff --git a/ifupdown2/lib/nlcache.py b/ifupdown2/lib/nlcache.py
index 0b7cedb226a96ed84f9ca1842d9bc560143a6c22..d94ad7a3b9e2d3a65a13cbe4cdc4904c49981597 100644 (file)
--- a/ifupdown2/lib/nlcache.py
+++ b/ifupdown2/lib/nlcache.py
@@ -2278,7 +2278,7 @@ class NetlinkListenerWithCache(nllistener.NetlinkManagerWithListener, BaseObject
 
         raise Exception(error_str)
 
-    def tx_nlpacket_get_response_with_error_and_cache_on_ack(self, packet):
+    def tx_nlpacket_get_response_with_error_and_cache_on_ack(self, packet, ifname=None):
         """
             TX packet and manually cache the object
         """
@@ -2302,6 +2302,33 @@ class NetlinkListenerWithCache(nllistener.NetlinkManagerWithListener, BaseObject
             # we can ignore all errors
             pass
 
+        try:
+            # We might be pre-caching an updated object that is "incomplete".
+            # i.e. say you have an existing bond in the cache, on ifreload only
+            # one attribute is updated. Our object 'packet' here will only have
+            # a couple attributes (but overriding a 'full' object in the cache).
+            # We need to somehow 'merge' some of the attributes that are not
+            # updated, otherwise later calls to the cache might return None for
+            # the missing attributes. MTU is a prime example.
+            if ifname:
+                # To minimize the changes each parent function can decide to
+                # trigger this 'merge' code by provided the optional 'ifname' arg
+
+                # MERGING MTU:
+                # First check if we are not already setting MTU in this packet
+                try:
+                    packet_mtu = packet.attributes[Link.IFLA_MTU].value
+                except Exception:
+                    packet_mtu = None
+                # Then update 'packet' before caching
+                if not packet_mtu:
+                    old_packet_mtu = self.cache.get_link_attribute(ifname, Link.IFLA_MTU)
+                    if old_packet_mtu:
+                        packet.add_attribute(Link.IFLA_MTU, old_packet_mtu)
+        except Exception:
+            # we can ignore all errors
+            pass
+
         # Then we can use our normal "add_link" API call to cache the packet
         # and fill up our additional internal data structures.
         self.cache.add_link(packet)
@@ -3060,7 +3087,7 @@ class NetlinkListenerWithCache(nllistener.NetlinkManagerWithListener, BaseObject
                 Link.IFLA_INFO_DATA: ifla_info_data
             })
             link.build_message(next(self.sequence), self.pid)
-            return self.tx_nlpacket_get_response_with_error_and_cache_on_ack(link)
+            return self.tx_nlpacket_get_response_with_error_and_cache_on_ack(link, ifname=ifname)
         except Exception as e:
             raise Exception("%s: netlink: cannot create bond with attributes: %s" % (ifname, str(e)))