dns-manager, config: make the dns config key single-valued

Make the main/dns config key be a single value rather than a list of
plugins. Since there is currently only one valid value for it
("dnsmasq"), this is backward-compatible.

In the future, it will be possible to specify custom DNS-configuring
scripts here, which is a more flexible way of handling complicated
behavior than trying to create chainable internal plugins.

man/NetworkManager.conf.5.in

@@ -135,17 +135,22 @@ no-auto-default=*
 Set devices for which NetworkManager should ignore device carrier state when
 deciding whether to activate or deactivate connections.
 .TP
-.B dns=\fIplugin1\fP,\fIplugin2\fP, ...
-List DNS plugin names separated by ','. DNS plugins are used to provide local
-caching nameserver functionality (which speeds up DNS queries) and to push
-DNS data to applications that use it.
+.B dns=\fImode\fP
+Set the DNS/resolv.conf-processing mode.
 .P
 .RS
-.B "Available plugins:"
+.B "Supported modes:"
 .br
 .TP
+.I default
+The default if the key is not specified. NetworkManager will update
+resolv.conf to reflect the nameservers provided by currently active
+connections.
+.TP
 .I dnsmasq
-this plugin uses dnsmasq to provide local caching nameserver functionality.
+NetworkManager will run dnsmasq as a local caching nameserver, using
+a "split DNS" configuration if you are connected to a VPN, and then
+update resolv.conf to point to the local nameserver.
 .RE
 .SS [keyfile]
 This section contains keyfile-specific options and thus only has effect when using \fIkeyfile\fP plugin.

src/config/nm-config.c

@@ -43,7 +43,7 @@ typedef struct {
 
 	char **plugins;
 	char *dhcp_client;
-	char **dns_plugins;
+	char *dns_mode;
 
 	char *log_level;
 	char *log_domains;
@@ -88,12 +88,12 @@ nm_config_get_dhcp_client (NMConfig *config)
 	return NM_CONFIG_GET_PRIVATE (config)->dhcp_client;
 }
 
-const char **
-nm_config_get_dns_plugins (NMConfig *config)
+const char *
+nm_config_get_dns_mode (NMConfig *config)
 {
 	g_return_val_if_fail (config != NULL, NULL);
 
-	return (const char **) NM_CONFIG_GET_PRIVATE (config)->dns_plugins;
+	return NM_CONFIG_GET_PRIVATE (config)->dns_mode;
 }
 
 const char *
@@ -492,7 +492,7 @@ nm_config_new (GError **error)
 	priv->plugins = g_key_file_get_string_list (priv->keyfile, "main", "plugins", NULL, NULL);
 
 	priv->dhcp_client = g_key_file_get_value (priv->keyfile, "main", "dhcp", NULL);
-	priv->dns_plugins = g_key_file_get_string_list (priv->keyfile, "main", "dns", NULL, NULL);
+	priv->dns_mode = g_key_file_get_value (priv->keyfile, "main", "dns", NULL);
 
 	if (cli_log_level && cli_log_level[0])
 		g_key_file_set_value (priv->keyfile, "logging", "level", cli_log_level);
@@ -541,7 +541,7 @@ finalize (GObject *gobject)
 	g_clear_pointer (&priv->keyfile, g_key_file_unref);
 	g_strfreev (priv->plugins);
 	g_free (priv->dhcp_client);
-	g_strfreev (priv->dns_plugins);
+	g_free (priv->dns_mode);
 	g_free (priv->log_level);
 	g_free (priv->log_domains);
 	g_free (priv->connectivity_uri);

src/config/nm-config.h

@@ -51,7 +51,7 @@ NMConfig *nm_config_get (void);
 const char *nm_config_get_path (NMConfig *config);
 const char **nm_config_get_plugins (NMConfig *config);
 const char *nm_config_get_dhcp_client (NMConfig *config);
-const char **nm_config_get_dns_plugins (NMConfig *config);
+const char *nm_config_get_dns_mode (NMConfig *config);
 const char *nm_config_get_log_level (NMConfig *config);
 const char *nm_config_get_log_domains (NMConfig *config);
 const char *nm_config_get_connectivity_uri (NMConfig *config);

src/dns-manager/nm-dns-manager.c

@@ -61,7 +61,7 @@ typedef struct {
 	guint8 hash[HASH_LEN];  /* SHA1 hash of current DNS config */
 	guint8 prev_hash[HASH_LEN];  /* Hash when begin_updates() was called */
 
-	GSList *plugins;
+	NMDnsPlugin *plugin;
 
 	gboolean dns_touched;
 } NMDnsManagerPrivate;
@@ -686,15 +686,15 @@ update_dns (NMDnsManager *self,
 	}
 
 	/* Let any plugins do their thing first */
-	for (iter = priv->plugins; iter; iter = g_slist_next (iter)) {
-		NMDnsPlugin *plugin = NM_DNS_PLUGIN (iter->data);
+	if (priv->plugin) {
+		NMDnsPlugin *plugin = priv->plugin;
 		const char *plugin_name = nm_dns_plugin_get_name (plugin);
 
 		if (nm_dns_plugin_is_caching (plugin)) {
 			if (no_caching) {
 				nm_log_dbg (LOGD_DNS, "DNS: plugin %s ignored (caching disabled)",
 				            plugin_name);
-				continue;
+				goto skip;
 			}
 			caching = TRUE;
 		}
@@ -712,7 +712,11 @@ update_dns (NMDnsManager *self,
 			 */
 			caching = FALSE;
 		}
+
+	skip:
+		;
 	}
+
 	g_slist_free (vpn_configs);
 	g_slist_free (dev_configs);
 	g_slist_free (other_configs);
@@ -1015,63 +1019,16 @@ nm_dns_manager_end_updates (NMDnsManager *mgr, const char *func)
 	memset (priv->prev_hash, 0, sizeof (priv->prev_hash));
 }
 
-static void
-load_plugins (NMDnsManager *self, const char **plugins)
-{
-	NMDnsManagerPrivate *priv = NM_DNS_MANAGER_GET_PRIVATE (self);
-	NMDnsPlugin *plugin;
-	const char **iter;
-	gboolean have_caching = FALSE;
-
-	if (plugins && *plugins) {
-		/* Create each configured plugin */
-		for (iter = plugins; iter && *iter; iter++) {
-			if (!strcasecmp (*iter, "dnsmasq"))
-				plugin = nm_dns_dnsmasq_new ();
-			else {
-				nm_log_warn (LOGD_DNS, "Unknown DNS plugin '%s'", *iter);\
-				continue;
-			}
-			g_assert (plugin);
-
-			/* Only one caching DNS plugin is allowed */
-			if (nm_dns_plugin_is_caching (plugin)) {
-				if (have_caching) {
-					nm_log_warn (LOGD_DNS,
-					             "Ignoring plugin %s; only one caching DNS "
-					             "plugin is allowed.",
-					             *iter);
-					g_object_unref (plugin);
-					continue;
-				}
-				have_caching = TRUE;
-			}
-
-			nm_log_info (LOGD_DNS, "DNS: loaded plugin %s", nm_dns_plugin_get_name (plugin));
-			priv->plugins = g_slist_append (priv->plugins, plugin);
-			g_signal_connect (plugin, NM_DNS_PLUGIN_FAILED,
-			                  G_CALLBACK (plugin_failed),
-			                  self);
-		}
-	} else {
-		/* Create default plugins */
-	}
-}
-
 /******************************************************************/
 
 NMDnsManager *
 nm_dns_manager_get (void)
 {
 	static NMDnsManager * singleton = NULL;
-	const char **plugins;
 
 	if (!singleton) {
 		singleton = NM_DNS_MANAGER (g_object_new (NM_TYPE_DNS_MANAGER, NULL));
 		g_assert (singleton);
-
-		plugins = nm_config_get_dns_plugins (nm_config_get ());
-		load_plugins (singleton, plugins);
 	} else
 		g_object_ref (singleton);
 
@@ -1091,8 +1048,22 @@ nm_dns_manager_error_quark (void)
 static void
 nm_dns_manager_init (NMDnsManager *self)
 {
+	NMDnsManagerPrivate *priv = NM_DNS_MANAGER_GET_PRIVATE (self);
+	const char *mode;
+
 	/* Set the initial hash */
 	compute_hash (self, NM_DNS_MANAGER_GET_PRIVATE (self)->hash);
+
+	mode = nm_config_get_dns_mode (nm_config_get ());
+	if (!g_strcmp0 (mode, "dnsmasq"))
+		priv->plugin = nm_dns_dnsmasq_new ();
+	else if (mode && g_strcmp0 (mode, "default") != 0)
+		nm_log_warn (LOGD_DNS, "Unknown DNS mode '%s'", mode);
+
+	if (priv->plugin) {
+		nm_log_info (LOGD_DNS, "DNS: loaded plugin %s", nm_dns_plugin_get_name (priv->plugin));
+		g_signal_connect (priv->plugin, NM_DNS_PLUGIN_FAILED, G_CALLBACK (plugin_failed), self);
+	}
 }
 
 static void
@@ -1102,8 +1073,7 @@ dispose (GObject *object)
 	NMDnsManagerPrivate *priv = NM_DNS_MANAGER_GET_PRIVATE (self);
 	GError *error = NULL;
 
-	g_slist_free_full (priv->plugins, g_object_unref);
-	priv->plugins = NULL;
+	g_clear_object (&priv->plugin);
 
 	/* If we're quitting, leave a valid resolv.conf in place, not one
 	 * pointing to 127.0.0.1 if any plugins were active.  Thus update