dns-manager: always apply options from [global-dns]

Currently, the use of [global-dns] section for setting DNS options is
conditioned on presence of a nameserver in a [global-dns-domain-*] section.
Attempt to use the section for options alone results in an error:

  [global-dns]
  options=timeout:1

Or via D-Bus API:

  # busctl set-property org.freedesktop.NetworkManager \
      /org/freedesktop/NetworkManager org.freedesktop.NetworkManager \
      GlobalDnsConfiguration 'a{sv}' 2 \
          "options" as 1 "timeout:1" \
          "domains" a{sv} 0
  ...
  Nov 24 13:15:21 zmok.local NetworkManager[501184]: <debug> [1669292121.3904]
      manager: set global DNS failed with error: Global
      DNS configuration is missing the default domain

The insistence on existence of [global-dns-domain-*] would make sense if
other [global-dns-domain-...] sections were present.

However, the user might only want to set the options in resolv.conf and
still use connection-provide nameservers for the actual resolving.

Lift the limitation by allowing the [global-dns] to be used alone, while
still insist on [global-dns-domain-*] being there in presence of other
domain-specific options.

https://bugzilla.redhat.com/show_bug.cgi?id=2019306

Makefile.am

@@ -4497,7 +4497,9 @@ EXTRA_DIST += \
 	src/core/tests/config/NetworkManager-warn.conf \
 	src/core/tests/config/NetworkManager.state \
 	src/core/tests/config/bad.conf \
+	src/core/tests/config/global-dns-good.conf \
 	src/core/tests/config/global-dns-invalid.conf \
+	src/core/tests/config/global-dns-options.conf \
 	src/core/tests/config/conf.d/00-overrides.conf \
 	src/core/tests/config/conf.d/10-more.conf \
 	src/core/tests/config/conf.d/20-config-enable-1.conf \

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

@@ -1201,7 +1201,8 @@ compute_hash(NMDnsManager *self, const NMGlobalDnsConfig *global, guint8 buffer[
 
     if (global)
         nm_global_dns_config_update_checksum(global, sum);
-    else {
+
+    if (!global || !nm_global_dns_config_lookup_domain(global, "*")) {
         const CList *head;
 
         /* FIXME(ip-config-checksum): this relies on the fact that an IP
@@ -1244,13 +1245,15 @@ merge_global_dns_config(NMResolvConfData *rc, NMGlobalDnsConfig *global_conf)
     }
 
     default_domain = nm_global_dns_config_lookup_domain(global_conf, "*");
-    nm_assert(default_domain);
+    if (!default_domain)
+        return TRUE;
 
     servers = nm_global_dns_domain_get_servers(default_domain);
-    if (servers) {
+    if (!servers)
-        for (i = 0; servers[i]; i++)
+        return TRUE;
-            add_string_item(rc->nameservers, servers[i], TRUE);
+
-    }
+    for (i = 0; servers[i]; i++)
+        add_string_item(rc->nameservers, servers[i], TRUE);
 
     return TRUE;
 }
@@ -1311,9 +1314,10 @@ _collect_resolv_conf_data(NMDnsManager      *self,
 
     priv = NM_DNS_MANAGER_GET_PRIVATE(self);
 
-    if (global_config) {
+    if (global_config)
         merge_global_dns_config(&rc, global_config);
-    } else {
+
+    if (!global_config || !nm_global_dns_config_lookup_domain(global_config, "*")) {
         nm_auto_str_buf NMStrBuf tmp_strbuf = NM_STR_BUF_INIT(0, FALSE);
         int                      first_prio = 0;
         const NMDnsConfigIPData *ip_data;
@@ -2556,14 +2560,12 @@ config_changed_cb(NMConfig           *config,
     }
 }
 
-static GVariant *
+static void
-_get_global_config_variant(NMGlobalDnsConfig *global)
+_get_global_config_variant(GVariantBuilder *builder, NMGlobalDnsConfig *global)
 {
     NMGlobalDnsDomain *domain;
-    GVariantBuilder    builder;
     guint              i, num;
 
-    g_variant_builder_init(&builder, G_VARIANT_TYPE("aa{sv}"));
     num = nm_global_dns_config_get_num_domains(global);
     for (i = 0; i < num; i++) {
         GVariantBuilder    conf_builder;
@@ -2599,10 +2601,8 @@ _get_global_config_variant(NMGlobalDnsConfig *global)
                               "priority",
                               g_variant_new_int32(NM_DNS_PRIORITY_DEFAULT_NORMAL));
 
-        g_variant_builder_add(&builder, "a{sv}", &conf_builder);
+        g_variant_builder_add(builder, "a{sv}", &conf_builder);
     }
-
-    return g_variant_ref_sink(g_variant_builder_end(&builder));
 }
 
 static GVariant *
@@ -2619,15 +2619,12 @@ _get_config_variant(NMDnsManager *self)
     if (priv->config_variant)
         return priv->config_variant;
 
-    global_config = nm_config_data_get_global_dns_config(nm_config_get_data(priv->config));
-    if (global_config) {
-        priv->config_variant = _get_global_config_variant(global_config);
-        _LOGT("current configuration: %s", (str = g_variant_print(priv->config_variant, TRUE)));
-        return priv->config_variant;
-    }
-
     g_variant_builder_init(&builder, G_VARIANT_TYPE("aa{sv}"));
 
+    global_config = nm_config_data_get_global_dns_config(nm_config_get_data(priv->config));
+    if (global_config)
+        _get_global_config_variant(&builder, global_config);
+
     head = _mgr_get_ip_data_lst_head(self);
     c_list_for_each_entry (ip_data, head, ip_data_lst) {
         GVariantBuilder    entry_builder;

src/core/nm-config-data.c

@@ -1233,7 +1233,7 @@ load_global_dns(GKeyFile *keyfile, gboolean internal)
             default_found = TRUE;
     }
 
-    if (!default_found) {
+    if (!default_found && g_hash_table_size(dns_config->domains)) {
         nm_log_dbg(LOGD_CORE,
                    "%s global DNS configuration is missing default domain, ignore it",
                    internal ? "internal" : "user");

src/core/tests/config/global-dns-good.conf

@@ -0,0 +1,13 @@
+# Good configuration, since there is a default domain section
+
+[global-dns]
+searches=foo.com
+options=timeout:5
+
+[global-dns-domain-*]
+servers=4.5.6.7
+options=myoption1
+
+[global-dns-domain-test.com]
+servers=1.2.3.4
+options=myoption2

src/core/tests/config/global-dns-options.conf

@@ -0,0 +1,5 @@
+# Good configuration, since there is no domain section
+
+[global-dns]
+searches=foo.com
+options=timeout:5

src/core/tests/config/test-config.c

@@ -370,7 +370,21 @@ test_config_global_dns(void)
 
     g_object_unref(config);
 
-    /* Check that a file without a default domain section gives a NULL configuration */
+    /* Check that a file with a default domain section gives a good configuration */
+    config =
+        setup_config(NULL, TEST_DIR "/global-dns-good.conf", "", NULL, "/no/such/dir", "", NULL);
+    dns = nm_config_data_get_global_dns_config(nm_config_get_data_orig(config));
+    g_assert(dns);
+    g_object_unref(config);
+
+    /* Check that a file with options but no domains gives a good configuration */
+    config =
+        setup_config(NULL, TEST_DIR "/global-dns-options.conf", "", NULL, "/no/such/dir", "", NULL);
+    dns = nm_config_data_get_global_dns_config(nm_config_get_data_orig(config));
+    g_assert(dns);
+    g_object_unref(config);
+
+    /* Check that a file with a domain domain, but without a default one gives a NULL configuration */
     config =
         setup_config(NULL, TEST_DIR "/global-dns-invalid.conf", "", NULL, "/no/such/dir", "", NULL);
     dns = nm_config_data_get_global_dns_config(nm_config_get_data_orig(config));