generator: use keep-configuration for NM

Network Manager will create external connection profiles for existing
interfaces. There are cases where it will happen, in particular with
virtual interfaces, during "netplan apply" even for interfaces that have
profiles.

"keep-configuration" forces NM to use the most appropriate profile for
existing interfaces.

Author: daniloegea

src/generate.c

@@ -304,9 +304,20 @@ int main(int argc, char** argv)
 
     /* Disable /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf
      * (which restricts NM to wifi and wwan) if "renderer: NetworkManager" is used anywhere */
-    if (netplan_state_get_backend(np_state) == NETPLAN_BACKEND_NM || any_nm)
+    if (netplan_state_get_backend(np_state) == NETPLAN_BACKEND_NM || any_nm) {
         _netplan_g_string_free_to_file(g_string_new(NULL), rootdir, "/run/NetworkManager/conf.d/10-globally-managed-devices.conf", NULL);
 
+        /*
+         * Always try to match existing interfaces with connections.
+         * Because "netplan apply" is too aggressive with Network Manager connections it might
+         * create in-memory profiles for existing virtual interfaces.
+         * keep-configuration forces NM to use existing connection profiles for these interfaces avoiding
+         * this problem.
+         */
+        _netplan_g_string_free_to_file(g_string_new("[device]\nkeep-configuration=no\n"), rootdir,
+                                       "/run/NetworkManager/conf.d/10-keep-configuration.conf", NULL);
+    }
+
     gboolean enable_wait_online = FALSE;
     if (any_networkd)
         enable_wait_online = _netplan_networkd_write_wait_online(np_state, rootdir);

src/nm.c

@@ -1185,8 +1185,11 @@ _netplan_nm_cleanup(const char* rootdir)
                                           "/run/NetworkManager/conf.d/netplan.conf", NULL);
     g_autofree char* global_manage_path = g_strjoin(NULL, rootdir != NULL ? rootdir : "",
                                                     "/run/NetworkManager/conf.d/10-globally-managed-devices.conf", NULL);
+    g_autofree char* keep_configuration_path = g_strjoin(NULL, rootdir != NULL ? rootdir : "",
+                                                    "/run/NetworkManager/conf.d/10-keep-configuration.conf", NULL);
     unlink(confpath);
     unlink(global_manage_path);
+    unlink(keep_configuration_path);
     _netplan_unlink_glob(rootdir, "/run/NetworkManager/system-connections/netplan-*");
     return TRUE;
 }