Index: share/man/man9/Makefile
===================================================================
--- share/man/man9/Makefile
+++ share/man/man9/Makefile
@@ -971,6 +971,7 @@
 MLINKS+=dev_clone.9 drain_dev_clone_events.9
 MLINKS+=dev_refthread.9 devvn_refthread.9 \
 	dev_refthread.9 dev_relthread.9
+MLINKS+=devctl_notify.9 devctl_notifyf.9
 MLINKS+=devfs_set_cdevpriv.9 devfs_clear_cdevpriv.9 \
 	devfs_set_cdevpriv.9 devfs_get_cdevpriv.9
 MLINKS+=device_add_child.9 device_add_child_ordered.9
Index: share/man/man9/devctl_notify.9
===================================================================
--- share/man/man9/devctl_notify.9
+++ share/man/man9/devctl_notify.9
@@ -23,16 +23,19 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 22, 2020
+.Dd March 9, 2022
 .Dt DEVCTL_NOTIFY 9
 .Os
 .Sh NAME
-.Nm devctl_notify
+.Nm devctl_notify ,
+.Nm devctl_notifyf
 .Nd Send a message, via devctl, to userland
 .Sh SYNOPSIS
 .In sys/devctl.h
 .Ft void
 .Fn devctl_notify "const char *system" "const char *subsystem" "const char *type" "const char *data"
+.Ft void
+.Fn devctl_notifyf "const char *system" "const char *subsystem" "const char *type" "const char *datafmt" "..."
 .Sh DESCRIPTION
 Send a notification to user land via
 .Xr devctl 4 .
@@ -66,11 +69,22 @@
 discover itself and sending all the data userland will want to use to
 decide what to do with the message.
 .Pp
+The
+.Fn devctl_notifyf
+function is identical to
+.Fn devctl_notify ,
+except it takes a format string to populate
+.Fa data
+and formats it as
+.Xr printf 9
+would print it.
+.Pp
 The current total message length limit is just under 1kb.
 Senders should try to remain well below this limit.
 .Sh SEE ALSO
 .Xr devctl 4 ,
-.Xr devd 8
+.Xr devd 8 ,
+.Xr printf 9
 .Sh AUTHORS
 This manual page was written by
 .An M. Warner Losh
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;