Re: [PATCH v2 1/5] driver core: add a faux bus for use when a simple device/bus is needed

[Zijun Hu]

On 2/4/2025 7:09 PM, Greg Kroah-Hartman wrote:
> +#define MAX_NAME_SIZE	256	/* Max size of a faux_device name */
> +
> +/*
> + * Internal wrapper structure so we can hold the memory
> + * for the driver and the name string of the faux device.
> + */
> +struct faux_object {
> +	struct faux_device faux_dev;
> +	const struct faux_driver_ops *faux_ops;
> +	char name[];

Remove name since it is not used actually ?

> +};+ */
> +void faux_device_destroy(struct faux_device *faux_dev)
> +{
> +	struct device *dev = &faux_dev->dev;
> +
> +	if (IS_ERR_OR_NULL(faux_dev))
> +		return;
> +

struct device *dev;

//faux_device_create() does not return ERR_PTR().
if (!faux_dev)
	return;

// avoid NULL pointer dereference in case of above error
dev = &faux_dev->dev;

> +	device_del(dev);
> +
> +	/* The final put_device() will clean up the driver we created for this device. */
> +	put_device(dev);

use device_unregister() instead of above 2 statements?

> +}
> +EXPORT_SYMBOL_GPL(faux_device_destroy);
> +
> +int __init faux_bus_init(void)
> +{
> +	int ret;
> +
> +	ret = device_register(&faux_bus_root);
> +	if (ret) {
> +		put_device(&faux_bus_root);

put_device() for static device may trigger below warning:

drivers/base/core.c:device_release():
WARN(1, KERN_ERR "Device '%s' does not have a release() function, it is
broken and must be fixed. See Documentation/core-api/kobject.rst.\n",
			dev_name(dev));
> +		return ret;
> +	}
> +
> +	ret = bus_register(&faux_bus_type);
> +	if (ret)
> +		goto error_bus;
> +


> +	ret = driver_register(&faux_driver);
> +	if (ret)
> +		goto error_driver;
> +
> +	return ret;
> +
> +error_driver:
> +	bus_unregister(&faux_bus_type);
> +
> +error_bus:
> +	device_unregister(&faux_bus_root);
> +	return ret;
> +}