Wayland: logging

The core libwayland libraries should not handle logging, only passing
the error messages to subscribed functions.
An application linked to libwayland-server or libwayland-client
will be able to set own functions (one per library) to handle error
messages.

Change in this series: make the wl_log return int, because
of compatibility with printf. It will return the number of bytes logged.

src/wayland-util.c

@@ -24,6 +24,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>
+#include <stdarg.h>
 
 #include "wayland-util.h"
 #include "wayland-private.h"
@@ -270,3 +271,20 @@ wl_map_for_each(struct wl_map *map, wl_iterator_func_t func, void *data)
 	for_each_helper(&map->client_entries, func, data);
 	for_each_helper(&map->server_entries, func, data);
 }
+
+static void
+wl_log_noop_handler(const char *fmt, va_list arg)
+{
+}
+
+wl_log_func_t wl_log_handler = wl_log_noop_handler;
+
+void
+wl_log(const char *fmt, ...)
+{
+	va_list argp;
+
+	va_start(argp, fmt);
+	wl_log_handler(fmt, argp);
+	va_end(argp);
+}