console: Support a format string for stderr output

Add a console_printf_select_stderr() function so that it is not
necessary for the caller to process the format string.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

common/console.c

@@ -359,6 +359,24 @@ void console_puts_select_stderr(bool serial_only, const char *s)
 		console_puts_select(stderr, serial_only, s);
 }
 
+int console_printf_select_stderr(bool serial_only, const char *fmt, ...)
+{
+	char buf[CONFIG_SYS_PBSIZE];
+	va_list args;
+	int ret;
+
+	va_start(args, fmt);
+
+	/* For this to work, buf must be larger than anything we ever want to
+	 * print.
+	 */
+	ret = vscnprintf(buf, sizeof(buf), fmt, args);
+	va_end(args);
+	console_puts_select_stderr(serial_only, buf);
+
+	return ret;
+}
+
 static void console_puts(int file, const char *s)
 {
 	int i;

include/console.h

@@ -169,6 +169,21 @@ int console_announce_r(void);
  */
 void console_puts_select_stderr(bool serial_only, const char *s);
 
+/**
+ * console_printf_select_stderr() - Output a formatted string to selected devs
+ *
+ * This writes to stderr only. It is useful for outputting errors. Note that it
+ * uses its own buffer, separate from the print buffer, to allow printing
+ * messages within console/stdio code
+ *
+ * @serial_only: true to output only to serial, false to output to everything
+ *	else
+ * @fmt: Printf format string, followed by format arguments
+ * Return: number of characters written
+ */
+int console_printf_select_stderr(bool serial_only, const char *fmt, ...)
+		__attribute__ ((format (__printf__, 2, 3)));
+
 /**
  * console_clear() - Clear the console
  *