add a default stderror log appender

src/lxc/log.c

@@ -38,12 +38,25 @@
 #define LXC_LOG_PREFIX_SIZE	32
 #define LXC_LOG_BUFFER_SIZE	512
 
-int lxc_log_fd = 2;
+int lxc_log_fd = -1;
 static char log_prefix[LXC_LOG_PREFIX_SIZE] = "lxc";
 
 lxc_log_define(lxc_log, lxc);
 
 /*---------------------------------------------------------------------------*/
+static int log_append_stderr(const struct lxc_log_appender *appender,
+			     struct lxc_log_event *event)
+{
+	if (event->priority < LXC_LOG_PRIORITY_ERROR)
+		return 0;
+
+	fprintf(stderr, "%s: ", log_prefix);
+	vfprintf(stderr, event->fmt, *event->vap);
+	fprintf(stderr, "\n");
+	return 0;
+}
+
+/*---------------------------------------------------------------------------*/
 static int log_append_logfile(const struct lxc_log_appender *appender,
 			      struct lxc_log_event *event)
 {
@@ -75,10 +88,16 @@ static int log_append_logfile(const struct lxc_log_appender *appender,
 	return write(lxc_log_fd, buffer, n + 1);
 }
 
+static struct lxc_log_appender log_appender_stderr = {
+	.name		= "stderr",
+	.append		= log_append_stderr,
+	.next		= NULL,
+};
+
 static struct lxc_log_appender log_appender_logfile = {
 	.name		= "logfile",
 	.append		= log_append_logfile,
-	.next		= NULL,
+	.next		= &log_appender_stderr,
 };
 
 static struct lxc_log_category log_root = {