dns: add "update-pending" state to NMDnsPlugin

Theoretically, this should be a GObject property, and not a signal.
But then I'd  also have to implement the get_property() function,
which is more hazzle than necessary. A signal will do nicely.

src/core/dns/nm-dns-plugin.c

@@ -17,8 +17,16 @@
 
 /*****************************************************************************/
 
+enum {
+    UPDATE_PENDING_CHANGED,
+    LAST_SIGNAL,
+};
+
+static guint signals[LAST_SIGNAL] = {0};
+
 typedef struct _NMDnsPluginPrivate {
-    int _dummy;
+    bool update_pending_inited : 1;
+    bool update_pending : 1;
 } NMDnsPluginPrivate;
 
 G_DEFINE_ABSTRACT_TYPE(NMDnsPlugin, nm_dns_plugin, G_TYPE_OBJECT)
@@ -104,6 +112,79 @@ nm_dns_plugin_stop(NMDnsPlugin *self)
 
 /*****************************************************************************/
 
+static gboolean
+_get_update_pending(NMDnsPlugin *self)
+{
+    NMDnsPluginClass *klass;
+
+    nm_assert(NM_IS_DNS_PLUGIN(self));
+
+    klass = NM_DNS_PLUGIN_GET_CLASS(self);
+    if (klass->get_update_pending) {
+        if (klass->get_update_pending(self))
+            return TRUE;
+    }
+    return FALSE;
+}
+
+gboolean
+nm_dns_plugin_get_update_pending(NMDnsPlugin *self)
+{
+    NMDnsPluginPrivate *priv;
+
+    g_return_val_if_fail(NM_IS_DNS_PLUGIN(self), FALSE);
+
+    priv = NM_DNS_PLUGIN_GET_PRIVATE(self);
+
+    /* We cache the boolean and rely on the subclass to call
+     * _nm_dns_plugin_update_pending_maybe_changed(). The subclass
+     * anyway must get it right to notify us when the value (maybe)
+     * changes. By caching the value, the subclass is free to notify
+     * even if the value did not actually change.
+     *
+     * Also, this allows the base implementation to combine multiple
+     * sources/reasons (if we need that in the future). */
+
+    if (!priv->update_pending_inited) {
+        priv->update_pending_inited = TRUE;
+        priv->update_pending        = _get_update_pending(self);
+        _LOGD("[%s] update-pending changed (%spending)",
+              nm_dns_plugin_get_name(self),
+              priv->update_pending ? "" : "not ");
+    } else
+        nm_assert(priv->update_pending == _get_update_pending(self));
+
+    return priv->update_pending;
+}
+
+void
+_nm_dns_plugin_update_pending_maybe_changed(NMDnsPlugin *self)
+{
+    NMDnsPluginPrivate *priv;
+    gboolean            v;
+
+    g_return_if_fail(NM_IS_DNS_PLUGIN(self));
+
+    priv = NM_DNS_PLUGIN_GET_PRIVATE(self);
+
+    v = _get_update_pending(self);
+
+    if (!priv->update_pending_inited)
+        priv->update_pending_inited = TRUE;
+    else if (priv->update_pending == v)
+        return;
+
+    priv->update_pending = v;
+
+    _LOGD("[%s] update-pending changed (%spending)",
+          nm_dns_plugin_get_name(self),
+          priv->update_pending ? "" : "not ");
+
+    g_signal_emit(self, signals[UPDATE_PENDING_CHANGED], 0, (gboolean) priv->update_pending);
+}
+
+/*****************************************************************************/
+
 static void
 nm_dns_plugin_init(NMDnsPlugin *self)
 {
@@ -113,6 +194,9 @@ nm_dns_plugin_init(NMDnsPlugin *self)
 
     self->_priv = priv;
 
+    nm_assert(priv->update_pending_inited == FALSE);
+    nm_assert(priv->update_pending == FALSE);
+
     nm_shutdown_wait_obj_register_object(self, "dns-plugin");
 }
 
@@ -122,4 +206,15 @@ nm_dns_plugin_class_init(NMDnsPluginClass *klass)
     GObjectClass *object_class = G_OBJECT_CLASS(klass);
 
     g_type_class_add_private(object_class, sizeof(NMDnsPluginPrivate));
+
+    signals[UPDATE_PENDING_CHANGED] = g_signal_new(NM_DNS_PLUGIN_UPDATE_PENDING_CHANGED,
+                                                   G_OBJECT_CLASS_TYPE(klass),
+                                                   G_SIGNAL_RUN_FIRST,
+                                                   0,
+                                                   NULL,
+                                                   NULL,
+                                                   NULL,
+                                                   G_TYPE_NONE,
+                                                   1,
+                                                   G_TYPE_BOOLEAN);
 }

src/core/dns/nm-dns-plugin.h

@@ -19,6 +19,8 @@
 #define NM_DNS_PLUGIN_GET_CLASS(obj) \
     (G_TYPE_INSTANCE_GET_CLASS((obj), NM_TYPE_DNS_PLUGIN, NMDnsPluginClass))
 
+#define NM_DNS_PLUGIN_UPDATE_PENDING_CHANGED "update-pending-changed"
+
 struct _NMDnsPluginPrivate;
 
 typedef struct {
@@ -42,6 +44,8 @@ typedef struct {
 
     void (*stop)(NMDnsPlugin *self);
 
+    gboolean (*get_update_pending)(NMDnsPlugin *self);
+
     const char *plugin_name;
 
     /* Types should set to TRUE if they start a local caching nameserver
@@ -66,4 +70,8 @@ gboolean nm_dns_plugin_update(NMDnsPlugin             *self,
 
 void nm_dns_plugin_stop(NMDnsPlugin *self);
 
+gboolean nm_dns_plugin_get_update_pending(NMDnsPlugin *self);
+
+void _nm_dns_plugin_update_pending_maybe_changed(NMDnsPlugin *self);
+
 #endif /* __NM_DNS_PLUGIN_H__ */