Ensure that all changes to generated files happen atomically.

NEWS

@@ -3,6 +3,8 @@ shared-mime-info		Thomas Leonard <tal00r@ecs.soton.ac.uk>
 
 			Version 0.10 (03-Mar-2003)
 
+* Ensure that all changes to generated files happen atomically.
+
 * Change to half-text, half-binary format to make parsing the magic file
   much easier.
 

update-mime-database.c

@@ -433,11 +433,29 @@ static void write_out_glob(gpointer key, gpointer value, gpointer data)
 	fprintf(stream, "%s/%s:%s\n", type->media, type->subtype, pattern);
 }
 
+/* Renames pathname by removing the .new extension */
+static void atomic_update(const guchar *pathname)
+{
+	guchar *new_name;
+	int len;
+
+	len = strlen(pathname);
+
+	g_return_if_fail(strcmp(pathname + len - 4, ".new") == 0);
+
+	new_name = g_strndup(pathname, len - 4);
+
+	if (rename(pathname, new_name))
+		g_warning("Failed to rename %s as %s\n", pathname, new_name);
+
+	g_free(new_name);
+}
+
 static void write_out_type(gpointer key, gpointer value, gpointer data)
 {
 	Type *type = (Type *) value;
 	const char *mime_dir = (char *) data;
-	char *media, *filename, *new_name;
+	char *media, *filename;
 
 	media = g_strconcat(mime_dir, "/", type->media, NULL);
 	mkdir(media, 0755);
@@ -449,13 +467,9 @@ static void write_out_type(gpointer key, gpointer value, gpointer data)
 	if (save_xml_file(type->output, filename) != 0)
 		g_warning("Failed to write out '%s'\n", filename);
 
-	new_name = g_strndup(filename, strlen(filename) - 4);
-	if (rename(filename, new_name))
-		g_warning("Failed to rename %s as %s\n",
-				filename, new_name);
+	atomic_update(filename);
 
 	g_free(filename);
-	g_free(new_name);
 }
 
 static int get_priority(xmlNode *node)
@@ -968,27 +982,29 @@ int main(int argc, char **argv)
 	{
 		FILE *globs;
 		char *globs_path;
-		globs_path = g_strconcat(mime_dir, "/globs", NULL);
+		globs_path = g_strconcat(mime_dir, "/globs.new", NULL);
 		globs = fopen(globs_path, "wb");
 		if (!globs)
 			g_error("Failed to open '%s' for writing\n", globs_path);
-		g_free(globs_path);
 		fprintf(globs,
 			"# This file was automatically generated by the\n"
 			"# update-mime-database command. DO NOT EDIT!\n");
 		g_hash_table_foreach(globs_hash, write_out_glob, globs);
 		fclose(globs);
+
+		atomic_update(globs_path);
+		g_free(globs_path);
 	}
 
 	{
 		FILE *stream;
 		char *magic_path;
 		int i;
-		magic_path = g_strconcat(mime_dir, "/magic", NULL);
+		magic_path = g_strconcat(mime_dir, "/magic.new", NULL);
 		stream = fopen(magic_path, "wb");
 		if (!stream)
-			g_error("Failed to open '%s' for writing\n", magic_path);
-		g_free(magic_path);
+			g_error("Failed to open '%s' for writing\n",
+					magic_path);
 		fwrite("MIME-Magic\0\n", 1, 12, stream);
 
 		if (magic->len)
@@ -1000,6 +1016,9 @@ int main(int argc, char **argv)
 			write_magic(stream, node);
 		}
 		fclose(stream);
+
+		atomic_update(magic_path);
+		g_free(magic_path);
 	}
 
 	{