dns: fall back to writing resolv.conf when other methods are not available

After commits:

de0d623680d7 dns: don't fall back to other methods when resolvconf or netconfig fail
e573977b8084 dns: allow runtime selection of resolv.conf manager

the method used to write /etc/resolv.conf is specified by a
configuration parameter and NM doesn't try other methods if the chosen
one has not success.

Restore the fallback to the 'none' method if resolvconf or netconfig
executables are not available, so that when the value of 'rc-manager'
is misconfigured the system continues to work properly.

https://bugzilla.gnome.org/show_bug.cgi?id=749286

1 files changed, 46 insertions, 30 deletions

diff --git a/src/dns-manager/nm-dns-manager.c b/src/dns-manager/nm-dns-manager.c
index 5c6b6e684a..09e3a1d66c 100644
--- a/src/dns-manager/nm-dns-manager.c
+++ b/src/dns-manager/nm-dns-manager.c
@@ -113,6 +113,12 @@ enum {
 	LAST_SIGNAL
 };
 
+typedef enum {
+	SR_SUCCESS,
+	SR_NOTFOUND,
+	SR_ERROR
+} SpawnResult;
+
 static guint signals[LAST_SIGNAL] = { 0 };
 
 
@@ -303,7 +309,7 @@ write_to_netconfig (gint fd, const char *key, const char *value)
 	g_free (str);
 }
 
-static gboolean
+static SpawnResult
 dispatch_netconfig (char **searches,
                     char **nameservers,
                     const char *nis_domain,
@@ -317,7 +323,7 @@ dispatch_netconfig (char **searches,
 
 	pid = run_netconfig (error, &fd);
 	if (pid <= 0)
-		return FALSE;
+		return SR_NOTFOUND;
 
 	/* NM is writing already-merged DNS information to netconfig, so it
 	 * does not apply to a specific network interface.
@@ -355,16 +361,16 @@ dispatch_netconfig (char **searches,
 		g_set_error (error, NM_MANAGER_ERROR, NM_MANAGER_ERROR_FAILED,
 		             "Error waiting for netconfig to exit: %s",
 		             strerror (errsv));
-		return FALSE;
+		return SR_ERROR;
 	}
 	if (!WIFEXITED (status) || WEXITSTATUS (status) != EXIT_SUCCESS) {
 		g_set_error (error, NM_MANAGER_ERROR, NM_MANAGER_ERROR_FAILED,
 		             "Error calling netconfig: %s %d",
 		             WIFEXITED (status) ? "exited with status" : (WIFSIGNALED (status) ? "exited with signal" : "exited with unknown reason"),
 		             WIFEXITED (status) ? WEXITSTATUS (status) : (WIFSIGNALED (status) ? WTERMSIG (status) : status));
-		return FALSE;
+		return SR_ERROR;
 	}
-	return TRUE;
+	return SR_SUCCESS;
 }
 
 static gboolean
@@ -436,7 +442,7 @@ write_resolv_conf (FILE *f,
 	return retval;
 }
 
-static gboolean
+static SpawnResult
 dispatch_resolvconf (char **searches,
                      char **nameservers,
                      char **options,
@@ -452,7 +458,7 @@ dispatch_resolvconf (char **searches,
 		                     NM_MANAGER_ERROR,
 		                     NM_MANAGER_ERROR_FAILED,
 		                     RESOLVCONF_PATH " is not executable");
-		return FALSE;
+		return SR_NOTFOUND;
 	}
 
 	if (searches || nameservers) {
@@ -487,14 +493,14 @@ dispatch_resolvconf (char **searches,
 
 	g_free (cmd);
 
-	return retval;
+	return retval ? SR_SUCCESS : SR_ERROR;
 }
 
 #define MY_RESOLV_CONF NMRUNDIR "/resolv.conf"
 #define MY_RESOLV_CONF_TMP MY_RESOLV_CONF ".tmp"
 #define RESOLV_CONF_TMP "/etc/.resolv.conf.NetworkManager"
 
-static gboolean
+static SpawnResult
 update_resolv_conf (char **searches,
                     char **nameservers,
 					char **options,
@@ -519,7 +525,7 @@ update_resolv_conf (char **searches,
 		if (ours) {
 			nm_log_dbg (LOGD_DNS, "not updating " MY_RESOLV_CONF
 			            " since it points to " _PATH_RESCONF);
-			return FALSE;
+			return SR_ERROR;
 		}
 	}
 
@@ -530,7 +536,7 @@ update_resolv_conf (char **searches,
 		             "Could not open %s: %s\n",
 		             MY_RESOLV_CONF_TMP,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
 	ret = write_resolv_conf (f, searches, nameservers, options, error);
@@ -550,7 +556,7 @@ update_resolv_conf (char **searches,
 	}
 
 	if (!ret)
-		return FALSE;
+		return SR_ERROR;
 
 	if (rename (MY_RESOLV_CONF_TMP, MY_RESOLV_CONF) < 0) {
 		g_set_error (error,
@@ -559,11 +565,11 @@ update_resolv_conf (char **searches,
 		             "Could not replace %s: %s\n",
 		             MY_RESOLV_CONF,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
 	if (!install_etc)
-		return TRUE;
+		return SR_SUCCESS;
 
 	/* Don't overwrite a symbolic link unless it points to MY_RESOLV_CONF. */
 	if (lstat (_PATH_RESCONF, &st) != -1) {
@@ -575,17 +581,17 @@ update_resolv_conf (char **searches,
 
 				g_free (path);
 				if (not_ours)
-					return TRUE;
+					return SR_SUCCESS;
 			} else {
 				if (errno != ENOENT)
-					return TRUE;
+					return SR_SUCCESS;
 				g_set_error (error,
 				             NM_MANAGER_ERROR,
 				             NM_MANAGER_ERROR_FAILED,
 				             "Could not stat %s: %s\n",
 				             _PATH_RESCONF,
 				             g_strerror (errno));
-				return FALSE;
+				return SR_ERROR;
 			}
 		}
 	} else if (errno != ENOENT) {
@@ -595,7 +601,7 @@ update_resolv_conf (char **searches,
 		             "Could not lstat %s: %s\n",
 		             _PATH_RESCONF,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
 	if (unlink (RESOLV_CONF_TMP) == -1 && errno != ENOENT) {
@@ -605,7 +611,7 @@ update_resolv_conf (char **searches,
 		             "Could not unlink %s: %s\n",
 		             RESOLV_CONF_TMP,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
 	if (symlink (MY_RESOLV_CONF, RESOLV_CONF_TMP) == -1) {
@@ -616,7 +622,7 @@ update_resolv_conf (char **searches,
 		             RESOLV_CONF_TMP,
 		             MY_RESOLV_CONF,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
 	if (rename (RESOLV_CONF_TMP, _PATH_RESCONF) == -1) {
@@ -627,10 +633,10 @@ update_resolv_conf (char **searches,
 		             RESOLV_CONF_TMP,
 		             _PATH_RESCONF,
 		             g_strerror (errno));
-		return FALSE;
+		return SR_ERROR;
 	}
 
-	return TRUE;
+	return SR_SUCCESS;
 }
 
 static void
@@ -722,7 +728,9 @@ update_dns (NMDnsManager *self,
 	char **nameservers = NULL;
 	char **nis_servers = NULL;
 	int num, i, len;
-	gboolean success = FALSE, caching = FALSE, update = TRUE;
+	gboolean caching = FALSE, update = TRUE;
+	gboolean resolv_conf_updated = FALSE;
+	SpawnResult result = SR_ERROR;
 
 	g_return_val_if_fail (!error || !*error, FALSE);
 
@@ -881,27 +889,35 @@ update_dns (NMDnsManager *self,
 	if (update) {
 		switch (priv->rc_manager) {
 		case NM_DNS_MANAGER_RESOLV_CONF_MAN_NONE:
-			success = update_resolv_conf (searches, nameservers, options, error, TRUE);
+			result = update_resolv_conf (searches, nameservers, options, error, TRUE);
+			resolv_conf_updated = TRUE;
 			break;
 		case NM_DNS_MANAGER_RESOLV_CONF_MAN_RESOLVCONF:
-			success = dispatch_resolvconf (searches, nameservers, options, error);
+			result = dispatch_resolvconf (searches, nameservers, options, error);
 			break;
 		case NM_DNS_MANAGER_RESOLV_CONF_MAN_NETCONFIG:
-			success = dispatch_netconfig (searches, nameservers, nis_domain,
-			                              nis_servers, error);
+			result = dispatch_netconfig (searches, nameservers, nis_domain,
+			                             nis_servers, error);
 			break;
 		default:
 			g_assert_not_reached ();
 		}
+
+		if (result == SR_NOTFOUND) {
+			nm_log_dbg (LOGD_DNS, "program not available, writing to resolv.conf");
+			g_clear_error (error);
+			result = update_resolv_conf (searches, nameservers, options, error, TRUE);
+			resolv_conf_updated = TRUE;
+		}
 	}
 
 	/* Unless we've already done it, update private resolv.conf in NMRUNDIR
 	   ignoring any errors */
-	if (!(update && priv->rc_manager == NM_DNS_MANAGER_RESOLV_CONF_MAN_NONE))
+	if (!resolv_conf_updated)
 		update_resolv_conf (searches, nameservers, options, NULL, FALSE);
 
 	/* signal that resolv.conf was changed */
-	if (update && success)
+	if (update && result == SR_SUCCESS)
 		g_signal_emit (self, signals[CONFIG_CHANGED], 0);
 
 	if (searches)
@@ -913,7 +929,7 @@ update_dns (NMDnsManager *self,
 	if (nis_servers)
 		g_strfreev (nis_servers);
 
-	return !update || success;
+	return !update || result == SR_SUCCESS;
 }
 
 static void