core: reverse the order of active connections in the manager

When a new active connection is created, it gets added at the
beginning of manager's list. This means that the list contains most
recently activated connections first. Since the list is doubly-linked,
it is possible to efficiently iterate in both directions, so the order
of the list is mostly a matter of convention.

I think it is preferable to have oldest active connections at the
beginning of the list; let's reverse the order.

In most places where the list is iterated, the order doesn't
matter. Where it does, use the *_prev() variant to maintain the old
iteration order.

4 files changed, 26 insertions, 6 deletions

diff --git a/.clang-format b/.clang-format
index b0233c0d09..33a0c63993 100644
--- a/.clang-format
+++ b/.clang-format
@@ -109,6 +109,7 @@ ForEachMacros: ['c_list_for_each',
                 'nm_l3_config_data_iter_ip6_route_for_each',
                 'nm_l3_config_data_iter_obj_for_each',
                 'nm_manager_for_each_active_connection',
+                'nm_manager_for_each_active_connection_prev',
                 'nm_manager_for_each_active_connection_safe',
                 'nm_manager_for_each_device',
                 'nm_manager_for_each_device_safe',
diff --git a/src/nm-manager.c b/src/nm-manager.c
index 55680bef92..c17c881b68 100644
--- a/src/nm-manager.c
+++ b/src/nm-manager.c
@@ -142,7 +142,7 @@ typedef struct {
 
     GArray *capabilities;
 
-    CList               active_connections_lst_head;
+    CList               active_connections_lst_head; /* Oldest ACs at the beginning */
     CList               async_op_lst_head;
     guint               ac_cleanup_id;
     NMActiveConnection *primary_connection;
@@ -941,7 +941,7 @@ active_connection_add(NMManager *self, NMActiveConnection *active)
     nm_assert(NM_IS_ACTIVE_CONNECTION(active));
     nm_assert(!c_list_is_linked(&active->active_connections_lst));
 
-    c_list_link_front(&priv->active_connections_lst_head, &active->active_connections_lst);
+    c_list_link_tail(&priv->active_connections_lst_head, &active->active_connections_lst);
     g_object_ref(active);
 
     g_signal_connect(active,
@@ -7867,7 +7867,9 @@ get_property(GObject *object, guint prop_id, GValue *value, GParamSpec *pspec)
         break;
     case PROP_ACTIVE_CONNECTIONS:
         ptrarr = g_ptr_array_new();
-        c_list_for_each_entry (ac, &priv->active_connections_lst_head, active_connections_lst) {
+        c_list_for_each_entry_prev (ac,
+                                    &priv->active_connections_lst_head,
+                                    active_connections_lst) {
             path = nm_dbus_object_get_path(NM_DBUS_OBJECT(ac));
             if (path)
                 g_ptr_array_add(ptrarr, g_strdup(path));
diff --git a/src/nm-manager.h b/src/nm-manager.h
index 75f8a673d0..fcb29cf562 100644
--- a/src/nm-manager.h
+++ b/src/nm-manager.h
@@ -72,6 +72,7 @@ NMState  nm_manager_get_state(NMManager *manager);
 
 const CList *nm_manager_get_active_connections(NMManager *manager);
 
+/* From least recently activated */
 #define nm_manager_for_each_active_connection(manager, iter, tmp_list)                        \
     for (tmp_list = nm_manager_get_active_connections(manager),                               \
         iter      = c_list_entry(tmp_list->next, NMActiveConnection, active_connections_lst); \
@@ -86,6 +87,22 @@ const CList *nm_manager_get_active_connections(NMManager *manager);
                              NMActiveConnection,                                              \
                              active_connections_lst))
 
+/* From most recently activated */
+#define nm_manager_for_each_active_connection_prev(manager, iter, tmp_list)                   \
+    for (tmp_list = nm_manager_get_active_connections(manager),                               \
+        iter      = c_list_entry(tmp_list->prev, NMActiveConnection, active_connections_lst); \
+         ({                                                                                   \
+             const gboolean _has_prev = (&iter->active_connections_lst != tmp_list);          \
+                                                                                              \
+             if (!_has_prev)                                                                  \
+                 iter = NULL;                                                                 \
+             _has_prev;                                                                       \
+         });                                                                                  \
+         iter = c_list_entry(iter->active_connections_lst.prev,                               \
+                             NMActiveConnection,                                              \
+                             active_connections_lst))
+
+/* From least recently activated */
 #define nm_manager_for_each_active_connection_safe(manager, iter, tmp_list, iter_safe)            \
     for (tmp_list = nm_manager_get_active_connections(manager), iter_safe = tmp_list->next; ({    \
              if (iter_safe != tmp_list) {                                                         \
diff --git a/src/nm-policy.c b/src/nm-policy.c
index 60f5fb024b..5a14a663ee 100644
--- a/src/nm-policy.c
+++ b/src/nm-policy.c
@@ -354,11 +354,11 @@ device_ip6_prefix_delegated(NMDevice *device, NMPlatformIP6Address *prefix, gpoi
     delegation->device = device;
     delegation->prefix = *prefix;
 
-    /* The newly activated connections are added to the list beginning,
-     * so traversing it from the beginning makes it likely for newly
+    /* The newly activated connections are added to the end of the list,
+     * so traversing it from the end makes it likely for newly
      * activated connections that have no subnet assigned to be served
      * first. That is a simple yet fair policy, which is good. */
-    nm_manager_for_each_active_connection (priv->manager, ac, tmp_list) {
+    nm_manager_for_each_active_connection_prev (priv->manager, ac, tmp_list) {
         NMDevice *to_device;
 
         to_device = nm_active_connection_get_device(ac);