vprintf: Add handler that mutes all output.

This adds a vprintf handler that can be used to suppress all outputs of
the libbsd.

libbsd.txt

@@ -265,6 +265,30 @@ their own implementation of the `rtems_bsd_get_allocator_domain_size()`
 function (for example in the module which calls `rtems_bsd_initialize()`) if
 different values are desired.  The default size is 8MiB for all domains.
 
+=== Redirecting or Disabling the Output ===
+
+A lot of system messages are printed to the stdout by default. If you want to
+redirect them you can overwrite the default print handler. That can even be done
+before the libbsd initialization to catch all messages. An example would look
+like follows:
+
+-------------------------------------------------------------------------------
+int my_vprintf_handler(int level, const char *fmt, va_list ap) {
+	/* Do something with the messages. */
+
+	return number_of_printed_chars;
+}
+
+...
+	/* In your initialization: */
+	rtems_bsd_vprintf_handler old;
+	old = rtems_bsd_set_vprintf_handler(my_vprintf_handler);
+...
+-------------------------------------------------------------------------------
+
+As a special case, you can set the `rtems_bsd_vprintf_handler_mute(...)`
+provided by libbsd to suppress all output.
+
 == Network Stack Features
 
 http://roy.marples.name/projects/dhcpcd/index[DHCPCD(8)]:: DHCP client

rtemsbsd/include/rtems/bsd/bsd.h

@@ -294,6 +294,15 @@ int rtems_bsd_vprintf(int level, const char *fmt, va_list ap);
  */
 int rtems_bsd_setlogpriority(const char* priority);
 
+/**
+ * @brief Set this vprintf handler to suppress all output.
+ *
+ * @retval Allways 0.
+ *
+ * @see rtems_bsd_vprintf() for the parameters.
+ */
+int rtems_bsd_vprintf_handler_mute(int level, const char *fmt, va_list ap);
+
 /** @} */
 
 #ifdef __cplusplus

rtemsbsd/rtems/rtems-kernel-vprintf.c

@@ -103,6 +103,16 @@ default_vprintf_handler(int level, const char *fmt, va_list ap)
 static int (*vprintf_handler)(int, const char *, va_list) =
     default_vprintf_handler;
 
+int
+rtems_bsd_vprintf_handler_mute(int level, const char *fmt, va_list ap)
+{
+	(void) level;
+	(void) fmt;
+	(void) ap;
+
+	return 0;
+}
+
 rtems_bsd_vprintf_handler
 rtems_bsd_set_vprintf_handler(rtems_bsd_vprintf_handler new_handler)
 {