[PATCH qemu-server v2 2/2] fix #6490: network: add bridge fdb entries when hotplugging a nic

["Rémi PAETA" <remi.paeta@comaite.com>]

On bridges with MAC learning disabled, the forwarding database entries
of the guest NICs are added on VM start and on resume after a
migration, but not when a NIC gets hotplugged or re-plugged because its
bridge, VLAN tag, trunks or firewall setting changed. Re-plugging even
drops the existing entries.

The guest then loses connectivity on that NIC until its next start or
migration, for example after enabling or disabling the firewall of the
NIC.

Add the forwarding database entries of the NIC after plugging it. On
bridges with MAC learning enabled, this is a no-op. As the NIC is
already plugged at that point, only warn if adding them fails, instead
of failing the update and leaving the configuration out of sync with
the running VM.

Link: https://bugzilla.proxmox.com/show_bug.cgi?id=6490
Signed-off-by: Rémi PAETA <remi.paeta@comaite.com>
---
 src/PVE/QemuServer.pm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index b4a1a38d..626dc78a 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -4994,6 +4994,9 @@ sub vmconfig_update_net {
                     $newnet->{trunks},
                     $newnet->{rate},
                 );
+                # unplugging the interface dropped its forwarding database entries
+                eval { PVE::QemuServer::Network::add_nets_bridge_fdb({ $opt => $value }, $vmid) };
+                log_warn("failed to add forwarding database entries of '$iface' - $@") if $@;
 
             } elsif (safe_num_ne($oldnet->{rate}, $newnet->{rate})) {
                 # Rate can be applied on its own but any change above needs to
@@ -5023,6 +5026,11 @@ sub vmconfig_update_net {
             $newnet->{bridge}, $newnet->{macaddr}, $vmid, $conf->{name},
         );
         vm_deviceplug($storecfg, $conf, $vmid, $opt, $newnet, $arch, $machine_type);
+        if ($newnet->{bridge}) {
+            # the NIC is plugged already, so do not fail the hotplug
+            eval { PVE::QemuServer::Network::add_nets_bridge_fdb({ $opt => $value }, $vmid) };
+            log_warn("failed to add forwarding database entries of '$opt' - $@") if $@;
+        }
     } else {
         die "skip\n";
     }
-- 
2.47.3