Index: sys/kern/subr_bus.c
===================================================================
--- sys/kern/subr_bus.c
+++ sys/kern/subr_bus.c
@@ -675,11 +675,13 @@
 }
 
 /**
- * @brief Send a 'notification' to userland, using standard ways
+ * @brief Send a 'notification' to userland, using standard ways.  This version
+ * takes a format string and varargs, which fits a number of consumers' slightly
+ * less trivial needs.
  */
 void
-devctl_notify(const char *system, const char *subsystem, const char *type,
-    const char *data)
+devctl_notifyf(const char *system, const char *subsystem, const char *type,
+    const char *datafmt, ...)
 {
 	struct dev_event_info *dei;
 	struct sbuf sb;
@@ -695,15 +697,35 @@
 	sbuf_cat(&sb, subsystem);
 	sbuf_cat(&sb, " type=");
 	sbuf_cat(&sb, type);
-	if (data != NULL) {
+	if (datafmt != NULL && *datafmt != '\0') {
+		va_list ap;
+
+		va_start(ap, datafmt);
 		sbuf_putc(&sb, ' ');
-		sbuf_cat(&sb, data);
+		sbuf_vprintf(&sb, datafmt, ap);
+		va_end(ap);
 	}
 	sbuf_putc(&sb, '\n');
 	if (sbuf_finish(&sb) != 0)
 		devctl_free_dei(dei);	/* overflow -> drop it */
 	else
 		devctl_queue(dei);
+
+}
+
+/**
+ * @brief Send a 'notification' to userland, using standard ways
+ */
+void
+devctl_notify(const char *system, const char *subsystem, const char *type,
+    const char *data)
+{
+
+	if (data != NULL) {
+		devctl_notifyf(system, subsystem, type, "%s", data);
+	} else {
+		devctl_notifyf(system, subsystem, type, NULL);
+	}
 }
 
 /*
Index: sys/sys/devctl.h
===================================================================
--- sys/sys/devctl.h
+++ sys/sys/devctl.h
@@ -13,6 +13,8 @@
  * hook to send the message.
  */
 bool devctl_process_running(void);
+void devctl_notifyf(const char *__system, const char *__subsystem,
+    const char *__type, const char *__datafmt, ...) __printflike(4, 5);
 void devctl_notify(const char *__system, const char *__subsystem,
     const char *__type, const char *__data);
 struct sbuf;