From 6e35cf4a7d709385b7c8e38ab41f8e62873a34eb Mon Sep 17 00:00:00 2001
From: Thomas Haller <thaller@redhat.com>
Date: Fri, 8 Apr 2022 11:40:42 +0200
Subject: [PATCH] core: add nm_manager_get_dns_manager() getter

nm_dns_manager_get() is already a singleton. So users usually
can just get it whenever they need -- except during shutdown
after the singleton was destroyed. This is usually fine, because
users really should not try to get it late during shutdown.

However, if you subscribe a signal handler on the singleton, then you
will also eventually want to unsubscribe it. While the moment when you
subscribe it is clearly not during late-shutdown, it's not clear how
to ensure that the signal listener gets destroyed before the DNS manager
singleton.

So usually, whenever you are going to subscribe a signal, you need to
make sure that the target object stays alive long enough. Which may
mean to keep a reference to it.

Next, we will have NMDevice subscribe to the singleton. With above said,
that would mean that potentially every NMDevice needs to keep a
reference to the NMDnsManager. That is not best. Also, later NMManager
will face the same problem, because it will also subscribe to
NMDnsManager.

So, instead let NMManager own a reference to the NMDnsManager. This
ensures the lifetimes are properly guarded (NMDevice also references
NMManager already).

Also, access nm_dns_manager_get() lazy on first use, to only initialize
it when needed the first time (which might be quite late).
---
 src/core/nm-manager.c | 27 +++++++++++++++++++++++++++
 src/core/nm-manager.h |  4 ++++
 2 files changed, 31 insertions(+)

diff --git a/src/core/nm-manager.c b/src/core/nm-manager.c
index 521536979f..fab316f4d4 100644
--- a/src/core/nm-manager.c
+++ b/src/core/nm-manager.c
@@ -20,6 +20,7 @@
 #include "devices/nm-device-factory.h"
 #include "devices/nm-device-generic.h"
 #include "devices/nm-device.h"
+#include "dns/nm-dns-manager.h"
 #include "dhcp/nm-dhcp-manager.h"
 #include "libnm-core-aux-intern/nm-common-macros.h"
 #include "libnm-core-intern/nm-core-internal.h"
@@ -144,6 +145,8 @@ NM_GOBJECT_PROPERTIES_DEFINE(NMManager,
 typedef struct {
     NMPlatform *platform;
 
+    NMDnsManager *dns_mgr;
+
     GArray *capabilities;
 
     CList               active_connections_lst_head; /* Oldest ACs at the beginning */
@@ -7790,6 +7793,28 @@ impl_manager_checkpoint_adjust_rollback_timeout(NMDBusObject
 
 /*****************************************************************************/
 
+NMDnsManager *
+nm_manager_get_dns_manager(NMManager *self)
+{
+    NMManagerPrivate *priv;
+
+    g_return_val_if_fail(NM_IS_MANAGER(self), NULL);
+
+    priv = NM_MANAGER_GET_PRIVATE(self);
+
+    if (G_UNLIKELY(!priv->dns_mgr)) {
+        /* Initialize lazily on first use.
+         *
+         * But keep a reference. This is to ensure proper lifetimes between
+         * singleton instances (i.e. nm_dns_manager_get() outlives NMManager). */
+        priv->dns_mgr = g_object_ref(nm_dns_manager_get());
+    }
+
+    return priv->dns_mgr;
+}
+
+/*****************************************************************************/
+
 static void
 auth_mgr_changed(NMAuthManager *auth_manager, gpointer user_data)
 {
@@ -8250,6 +8275,8 @@ dispose(GObject *object)
         g_clear_object(&priv->concheck_mgr);
     }
 
+    g_clear_object(&priv->dns_mgr);
+
     if (priv->auth_mgr) {
         g_signal_handlers_disconnect_by_func(priv->auth_mgr, G_CALLBACK(auth_mgr_changed), self);
         g_clear_object(&priv->auth_mgr);
diff --git a/src/core/nm-manager.h b/src/core/nm-manager.h
index f8563c3aa1..fcb0022720 100644
--- a/src/core/nm-manager.h
+++ b/src/core/nm-manager.h
@@ -200,6 +200,10 @@ NMMetered nm_manager_get_metered(NMManager *self);
 
 void nm_manager_notify_device_availability_maybe_changed(NMManager *self);
 
+struct _NMDnsManager;
+
+struct _NMDnsManager *nm_manager_get_dns_manager(NMManager *self);
+
 /*****************************************************************************/
 
 void nm_manager_device_auth_request(NMManager                     *self,