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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.
*/

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