Index: share/man/man9/module.9
===================================================================
--- share/man/man9/module.9
+++ share/man/man9/module.9
@@ -28,12 +28,18 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 12, 2018
+.Dd May 27, 2019
 .Dt MODULE 9
 .Os
 .Sh NAME
 .Nm module
 .Nd structure describing a kernel module
+.Sh SYNOPSIS
+.In sys/param.h
+.In sys/kernel.h
+.In sys/module.h
+.Ft int
+.Fn modevent_nop "module_t" "int" "void *"
 .Sh DESCRIPTION
 Each module in the kernel is described by a
 .Vt module_t
@@ -47,6 +53,11 @@
 .Xr DECLARE_MODULE 9
 macro
 registers the module with the system.
+.Xr DRIVER_MODULE 9
+is a convenience wrapper around
+.Fn DECLARE_MODULE
+for device drivers.
+Modules only need one.
 .Pp
 When the module is loaded, the event handler function is called with
 the
@@ -65,7 +76,7 @@
 .Fa what
 is set to
 .Dv MOD_UNLOAD .
-If the module returns non-zero to this, the unload will not happen.
+If the module returns non-zero to this, unload fails.
 .Pp
 The difference between
 .Dv MOD_QUIESCE
@@ -75,8 +86,9 @@
 .Dv MOD_QUIESCE
 if it is currently in use, whereas
 .Dv MOD_UNLOAD
-should only fail if it is impossible to unload the module, for instance
-because there are memory references to the module which cannot be revoked.
+should only fail if it is impossible to unload the module.
+For instance, because there are memory references to the module which cannot be
+revoked.
 .Pp
 When the system is shutting down,
 .Fa what
@@ -87,6 +99,11 @@
 .Er EOPNOTSUPP
 for unsupported and unrecognized values of
 .Fa what .
+.Pp
+.Fn modevent_nop
+is provided as a helper routine for simple modules.
+It does nothing and returns zero in response to all valid events.
+It returns EOPTNOTSUPP in response to invalid events.
 .Sh EXAMPLES
 .Bd -literal
 #include <sys/param.h>
Index: sys/kern/kern_module.c
===================================================================
--- sys/kern/kern_module.c
+++ sys/kern/kern_module.c
@@ -66,7 +66,7 @@
 static void module_shutdown(void *, int);
 
 static int
-modevent_nop(module_t mod, int what, void *arg)
+modevent_no_unload(module_t mod, int what, void *arg)
 {
 
 	switch(what) {
@@ -79,6 +79,26 @@
 	}
 }
 
+int
+modevent_nop(module_t mod __unused, int type, void *unused __unused)
+{
+	int error;
+
+	switch (type) {
+	case MOD_LOAD:
+	case MOD_QUIESCE:
+	case MOD_UNLOAD:
+	case MOD_SHUTDOWN:
+		error = 0;
+		break;
+	default:
+		error = EOPNOTSUPP;
+		break;
+	}
+
+	return (error);
+}
+
 static void
 module_init(void *arg)
 {
@@ -168,7 +188,7 @@
 	newmod->id = nextid++;
 	newmod->name = (char *)(newmod + 1);
 	strcpy(newmod->name, data->name);
-	newmod->handler = data->evhand ? data->evhand : modevent_nop;
+	newmod->handler = data->evhand ? data->evhand : modevent_no_unload;
 	newmod->arg = data->priv;
 	bzero(&newmod->data, sizeof(newmod->data));
 	TAILQ_INSERT_TAIL(&modules, newmod, link);
Index: sys/sys/module.h
===================================================================
--- sys/sys/module.h
+++ sys/sys/module.h
@@ -52,6 +52,13 @@
 typedef struct module *module_t;
 typedef int (*modeventhand_t)(module_t, int /* modeventtype_t */, void *);
 
+/*
+ * A module can use this to ignore all valid module events.  (In contrast, a
+ * NULL eventhandler prevents module unload with EBUSY, and returns EOPNOTSUPP
+ * for QUIESCE and SHUTDOWN.)
+ */
+int modevent_nop(module_t, int, void *);
+
 /*
  * Struct for registering modules statically via SYSINIT.
  */