um: Add os_info() for pre-boot information messages

Add os_info() for printing out pre-boot information
level messages in stderr. The messages via os_info()
are suppressed by "quiet" kernel command line.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/os-Linux/util.c

@@ -13,6 +13,7 @@
 #include <wait.h>
 #include <sys/mman.h>
 #include <sys/utsname.h>
+#include <init.h>
 #include <os.h>
 
 void stack_protections(unsigned long address)
@@ -152,3 +153,27 @@ void um_early_printk(const char *s, unsigned int n)
 {
 	printf("%.*s", n, s);
 }
+
+static int quiet_info;
+
+static int __init quiet_cmd_param(char *str, int *add)
+{
+	quiet_info = 1;
+	return 0;
+}
+
+__uml_setup("quiet", quiet_cmd_param,
+"quiet\n"
+"    Turns off information messages during boot.\n\n");
+
+void os_info(const char *fmt, ...)
+{
+	va_list list;
+
+	if (quiet_info)
+		return;
+
+	va_start(list, fmt);
+	vfprintf(stderr, fmt, list);
+	va_end(list);
+}