virtio: store owner from modules with register_virtio_driver()

Modules registering driver with register_virtio_driver() might forget to
set .owner field.  i2c-virtio.c for example has it missing.  The field
is used by some other kernel parts for reference counting
(try_module_get()), so it is expected that drivers will set it.

Solve the problem by moving this task away from the drivers to the core
virtio code, just like we did for platform_driver in
commit 9447057e ("platform_device: use a macro instead of
platform_driver_register").

Fixes: 3cfc8838 ("i2c: virtio: add a virtio i2c frontend driver")
Cc: "Jie Deng" <jie.deng@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Message-Id: <20240331-module-owner-virtio-v2-1-98f04bfaf46a@linaro.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Documentation/driver-api/virtio/writing_virtio_drivers.rst

@@ -97,7 +97,6 @@ like this::
 
 	static struct virtio_driver virtio_dummy_driver = {
 		.driver.name =  KBUILD_MODNAME,
-		.driver.owner = THIS_MODULE,
 		.id_table =     id_table,
 		.probe =        virtio_dummy_probe,
 		.remove =       virtio_dummy_remove,

drivers/virtio/virtio.c

@@ -362,14 +362,16 @@ static const struct bus_type virtio_bus = {
 	.remove = virtio_dev_remove,
 };
 
-int register_virtio_driver(struct virtio_driver *driver)
+int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
 {
 	/* Catch this early. */
 	BUG_ON(driver->feature_table_size && !driver->feature_table);
 	driver->driver.bus = &virtio_bus;
+	driver->driver.owner = owner;
+
 	return driver_register(&driver->driver);
 }
-EXPORT_SYMBOL_GPL(register_virtio_driver);
+EXPORT_SYMBOL_GPL(__register_virtio_driver);
 
 void unregister_virtio_driver(struct virtio_driver *driver)
 {

include/linux/virtio.h

@@ -170,7 +170,7 @@ size_t virtio_max_dma_size(const struct virtio_device *vdev);
 
 /**
  * struct virtio_driver - operations for a virtio I/O driver
- * @driver: underlying device driver (populate name and owner).
+ * @driver: underlying device driver (populate name).
  * @id_table: the ids serviced by this driver.
  * @feature_table: an array of feature numbers supported by this driver.
  * @feature_table_size: number of entries in the feature table array.
@@ -208,7 +208,10 @@ static inline struct virtio_driver *drv_to_virtio(struct device_driver *drv)
 	return container_of(drv, struct virtio_driver, driver);
 }
 
-int register_virtio_driver(struct virtio_driver *drv);
+/* use a macro to avoid include chaining to get THIS_MODULE */
+#define register_virtio_driver(drv) \
+	__register_virtio_driver(drv, THIS_MODULE)
+int __register_virtio_driver(struct virtio_driver *drv, struct module *owner);
 void unregister_virtio_driver(struct virtio_driver *drv);
 
 /* module_virtio_driver() - Helper macro for drivers that don't do