Index: sys/kern/sys_eventfd.c
===================================================================
--- sys/kern/sys_eventfd.c
+++ sys/kern/sys_eventfd.c
@@ -154,6 +154,21 @@
 	free(efd, M_EVENTFD);
 }
 
+void
+eventfd_signal_mask(struct eventfd_ctx *efd, unsigned int mask __unused)
+{
+	mtx_lock(&efd->efd_lock);
+
+	if (efd->efd_count < UINT64_MAX)
+		efd->efd_count++;
+
+	KNOTE_LOCKED(&efd->efd_sel.si_note, 0);
+	selwakeup(&efd->efd_sel);
+	wakeup(&efd->efd_count);
+
+	mtx_unlock(&efd->efd_lock);
+}
+
 static int
 eventfd_close(struct file *fp, struct thread *td)
 {
Index: sys/sys/eventfd.h
===================================================================
--- sys/sys/eventfd.h
+++ sys/sys/eventfd.h
@@ -44,6 +44,7 @@
     int flags);
 struct eventfd_ctx *eventfd_get(struct file *fp);
 void eventfd_put(struct eventfd_ctx *efd);
+void eventfd_signal_mask(struct eventfd_ctx *efd, unsigned int mask);
 
 #else