dev: implement generic devices

generic devices don't have a type (char, block, etc) and are created
by bus drivers to represent the device until a suitable driver is found.

generic devices are registered by the bus driver. once a more suitable
driver is found, that driver will re-register the device under itself.

dev/driver.c

@@ -44,13 +44,10 @@ struct driver *driver_create(struct kext *self, const char *name)
 		return NULL;
 	}
 
-	memset(driver, 0x0, sizeof *driver);
-
-	driver->drv_owner = self;
-	strncpy(driver->drv_name, name, sizeof driver->drv_name - 1);
-	driver->drv_name[sizeof driver->drv_name - 1] = 0;
-
-	bitmap_set(driver->drv_minors, DEV_MINOR_INVALID);
+	if (driver_init(driver, self, name) != KERN_OK) {
+		vm_cache_free(&driver_cache, driver);
+		return NULL;
+	}
 
 	return driver;
 }
@@ -61,6 +58,30 @@ kern_status_t driver_destroy(struct driver *driver)
 		return KERN_BUSY;
 	}
 
+	kern_status_t status = driver_deinit(driver);
+	if (status != KERN_OK) {
+		return status;
+	}
+
+	vm_cache_free(&driver_cache, driver);
+	return KERN_OK;
+}
+
+kern_status_t driver_init(struct driver *driver, struct kext *self, const char *name)
+{
+	memset(driver, 0x0, sizeof *driver);
+
+	driver->drv_owner = self;
+	strncpy(driver->drv_name, name, sizeof driver->drv_name - 1);
+	driver->drv_name[sizeof driver->drv_name - 1] = 0;
+
+	bitmap_set(driver->drv_minors, DEV_MINOR_INVALID);
+	return KERN_OK;
+}
+
+kern_status_t driver_deinit(struct driver *driver)
+{
+	/* TODO */
 	return KERN_UNIMPLEMENTED;
 }
 
@@ -91,7 +112,7 @@ kern_status_t driver_register(struct driver *driver)
 	put_driver(&drivers, driver);
 
 	spin_unlock_irqrestore(&drivers_lock, flags);
-	return KERN_UNIMPLEMENTED;
+	return KERN_OK;
 }
 
 kern_status_t driver_unregister(struct driver *driver)
@@ -147,3 +168,9 @@ kern_status_t driver_add_device(struct driver *driver, struct device *dev)
 
 	return KERN_OK;
 }
+
+kern_status_t driver_remove_device(struct driver *driver, struct device *dev)
+{
+	btree_delete(&driver->drv_children, &dev->dev_driverent);
+	return KERN_OK;
+}