config: allow to enable/disable configuration snippets

Support a new configuration option

  [.config]
  enable=<ENABLED>

for configuration snippets.

This new [.config] section is only relevant within the snippet itself
and it is not merged into the combined configuration.

Currently only the "enable" key is supported. If the "enable" key is
missing, it obviously defaults to being enabled. It allows snippets
to be skipped from loading. The main configuration "NetworkManager.conf"
cannot be skipped.

<ENABLED> can be a boolean value (false), to skip a configuration
snippet from loading.
It can also be a string to match against the NetworkManager version,
like "enable=nm-version-min:1.1,nm-version-min:1.0.6"

There are several motivations for this:

- the user can disable an entire configuration snippet by toggeling
  one entry.
  This generalizes  the functionality of the global-dns.enable
  setting, but in a way that applies to configuration on a per-file
  basis.

- for developing, we often switch between different versions of
  NetworkManager. Thus, we might want to use different configuration.
  E.g. before global-dns options, I want to use "dns=none" and manage
  resolv.conf myself. Now, I can use global-dns setting to do that.
  That can be achieved with something like the following (not exactly,
  it's an example only):

      [.config]
      enable=nm-version-min:1.1
      [main]
      dns=default
      [global-dns-domain-*]
      nameserver=127.0.0.1

  Arguably, this would be more awesome, if we would bump our micro devel
  version (1.1.0) more often while developing 1.2.0 (*hint*).

- in principle, packages could drop configuration snippets and enable
  them based on the NetworkManager version.

- with the "env:" spec, you can enable/disable snippets by configuring
  an environment variable. Again, useful for testing and developing.

1 files changed, 60 insertions, 6 deletions

diff --git a/src/nm-config.c b/src/nm-config.c
index fb9f0be988..f8c4ee817d 100644
--- a/src/nm-config.c
+++ b/src/nm-config.c
@@ -495,6 +495,47 @@ nm_config_create_keyfile ()
 	return keyfile;
 }
 
+/* this is an external variable, to make loading testable. Other then that,
+ * no code is supposed to change this. */
+guint _nm_config_match_nm_version = NM_VERSION_CUR_STABLE;
+char *_nm_config_match_env = NULL;
+
+static gboolean
+ignore_config_snippet (GKeyFile *keyfile, gboolean is_base_config)
+{
+	GSList *specs;
+	gboolean as_bool;
+	NMMatchSpecMatchType match_type;
+
+	if (is_base_config)
+		return FALSE;
+
+	if (!g_key_file_has_key (keyfile, NM_CONFIG_KEYFILE_GROUP_CONFIG, NM_CONFIG_KEYFILE_KEY_CONFIG_ENABLE, NULL))
+		return FALSE;
+
+	/* first, let's try to parse the value as plain boolean. If that is possible, we don't treat
+	 * the value as match-spec. */
+	as_bool = nm_config_keyfile_get_boolean (keyfile, NM_CONFIG_KEYFILE_GROUP_CONFIG, NM_CONFIG_KEYFILE_KEY_CONFIG_ENABLE, -1);
+	if (as_bool != -1)
+		return !as_bool;
+
+	if (G_UNLIKELY (!_nm_config_match_env)) {
+		const char *e;
+
+		e = g_getenv ("NM_CONFIG_ENABLE_TAG");
+		_nm_config_match_env = g_strdup (e ? e : "");
+	}
+
+	/* second, interpret the value as match-spec. */
+	specs = nm_config_get_match_spec (keyfile, NM_CONFIG_KEYFILE_GROUP_CONFIG, NM_CONFIG_KEYFILE_KEY_CONFIG_ENABLE, NULL);
+	match_type = nm_match_spec_match_config (specs,
+	                                         _nm_config_match_nm_version,
+	                                         _nm_config_match_env);
+	g_slist_free_full (specs, g_free);
+
+	return match_type != NM_MATCH_SPEC_MATCH;
+}
+
 static int
 _sort_groups_cmp (const char **pa, const char **pb, gpointer dummy)
 {
@@ -568,7 +609,7 @@ _setting_is_string_list (const char *group, const char *key)
 }
 
 static gboolean
-read_config (GKeyFile *keyfile, const char *dirname, const char *path, GError **error)
+read_config (GKeyFile *keyfile, gboolean is_base_config, const char *dirname, const char *path, GError **error)
 {
 	GKeyFile *kf;
 	char **groups, **keys;
@@ -598,6 +639,16 @@ read_config (GKeyFile *keyfile, const char *dirname, const char *path, GError **
 		return FALSE;
 	}
 
+	if (ignore_config_snippet (kf, is_base_config)) {
+		g_key_file_free (kf);
+		return TRUE;
+	}
+
+	/* the config-group is internal to every configuration snippets. It doesn't make sense
+	 * to merge the into the global configuration, and it doesn't make sense to preserve the
+	 * group beyond this point. */
+	g_key_file_remove_group (keyfile, NM_CONFIG_KEYFILE_GROUP_CONFIG, NULL);
+
 	/* Override the current settings with the new ones */
 	groups = g_key_file_get_groups (kf, &ngroups);
 	if (!groups)
@@ -744,7 +795,7 @@ read_base_config (GKeyFile *keyfile,
 	/* Try a user-specified config file first */
 	if (cli_config_main_file) {
 		/* Bad user-specific config file path is a hard error */
-		if (read_config (keyfile, NULL, cli_config_main_file, error)) {
+		if (read_config (keyfile, TRUE, NULL, cli_config_main_file, error)) {
 			*out_config_main_file = g_strdup (cli_config_main_file);
 			return TRUE;
 		} else
@@ -759,7 +810,7 @@ read_base_config (GKeyFile *keyfile,
 	 */
 
 	/* Try deprecated nm-system-settings.conf first */
-	if (read_config (keyfile, NULL, DEFAULT_CONFIG_MAIN_FILE_OLD, &my_error)) {
+	if (read_config (keyfile, TRUE, NULL, DEFAULT_CONFIG_MAIN_FILE_OLD, &my_error)) {
 		*out_config_main_file = g_strdup (DEFAULT_CONFIG_MAIN_FILE_OLD);
 		return TRUE;
 	}
@@ -772,7 +823,7 @@ read_base_config (GKeyFile *keyfile,
 	g_clear_error (&my_error);
 
 	/* Try the standard config file location next */
-	if (read_config (keyfile, NULL, DEFAULT_CONFIG_MAIN_FILE, &my_error)) {
+	if (read_config (keyfile, TRUE, NULL, DEFAULT_CONFIG_MAIN_FILE, &my_error)) {
 		*out_config_main_file = g_strdup (DEFAULT_CONFIG_MAIN_FILE);
 		return TRUE;
 	}
@@ -878,7 +929,7 @@ read_entire_config (const NMConfigCmdLineOptions *cli,
 			continue;
 		}
 
-		if (!read_config (keyfile, system_config_dir, filename, error)) {
+		if (!read_config (keyfile, FALSE, system_config_dir, filename, error)) {
 			g_key_file_free (keyfile);
 			return NULL;
 		}
@@ -894,7 +945,7 @@ read_entire_config (const NMConfigCmdLineOptions *cli,
 	g_assert (o_config_main_file);
 
 	for (i = 0; i < confs->len; i++) {
-		if (!read_config (keyfile, config_dir, confs->pdata[i], error)) {
+		if (!read_config (keyfile, FALSE, config_dir, confs->pdata[i], error)) {
 			g_key_file_free (keyfile);
 			return NULL;
 		}
@@ -1067,6 +1118,9 @@ intern_config_read (const char *filename,
 		const char *group = groups[g];
 		gboolean is_intern, is_atomic;
 
+		if (!strcmp (group, NM_CONFIG_KEYFILE_GROUP_CONFIG))
+			continue;
+
 		keys = g_key_file_get_keys (keyfile, group, NULL, NULL);
 		if (!keys)
 			continue;