* Move the driver_t::refs field to kobj_t to replace kobj_t::instances.

* Back out a couple of workarounds for the confusion between
  kobj_t::instances and driver_t::refs.

sys/kern/subr_bus.c

@@ -162,7 +162,10 @@ devclass_add_driver(devclass_t dc, driver_t *driver)
     bzero(dl, sizeof *dl);
 
     /*
-     * Compile the driver's methods.
+     * Compile the driver's methods. Also increase the reference count
+     * so that the class doesn't get freed when the last instance
+     * goes. This means we can safely use static methods and avoids a
+     * double-free in devclass_delete_driver.
      */
     kobj_class_compile((kobj_class_t) driver);
 
@@ -986,7 +989,6 @@ device_set_driver(device_t dev, driver_t *driver)
 	    return ENOMEM;
 	}
 	bzero(dev->softc, driver->size);
-	driver->refs++;
     } else
 	kobj_init((kobj_t) dev, &null_class);
     return 0;
@@ -1843,11 +1845,6 @@ bus_generic_driver_added(device_t dev, driver_t *driver)
 {
     device_t child;
 
-    /*
-     * Make sure the class has a valid ops table.
-     */
-    kobj_class_compile((kobj_class_t) driver);
-
     DEVICE_IDENTIFY(driver, dev);
     for (child = TAILQ_FIRST(&dev->children);
 	 child; child = TAILQ_NEXT(child, link))

sys/kern/subr_kobj.c

@@ -174,7 +174,7 @@ kobj_init(kobj_t obj, kobj_class_t cls)
 		kobj_class_compile(cls);
 
 	obj->ops = cls->ops;
-	cls->instances++;
+	cls->refs++;
 }
 
 void
@@ -187,8 +187,8 @@ kobj_delete(kobj_t obj, struct malloc_type *mtype)
 	 * after its last instance is deleted. As an optimisation, we
 	 * should defer this for a short while to avoid thrashing.
 	 */
-	cls->instances--;
-	if (!cls->instances)
+	cls->refs--;
+	if (!cls->refs)
 		kobj_class_free(cls);
 
 	obj->ops = 0;

sys/sys/bus.h

@@ -65,7 +65,6 @@ typedef int (*devop_t)(void);
 struct driver {
     KOBJ_CLASS_FIELDS;
     void		*priv;		/* driver private data */
-    int			refs;		/* # devclasses containing driver */
 };
 
 typedef enum device_state {

sys/sys/kobj.h

@@ -55,7 +55,7 @@ struct kobj_method {
 	const char	*name;		/* class name */		\
 	kobj_method_t	*methods;	/* method table */		\
 	size_t		size;		/* object size */		\
-	u_int		instances;	/* instance count */		\
+	u_int		refs;		/* reference count */		\
 	kobj_ops_t	ops		/* compiled method table */
 
 struct kobj_class {