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

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Message-ID: <f575978b-7103-48b9-8125-a38fb6425f5c@quicinc.com>
Date: Thu, 6 Feb 2025 23:34:27 +0800
From: Zijun Hu <quic_zijuhu@...cinc.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Danilo Krummrich <dakr@...nel.org>, Lyude Paul <lyude@...hat.com>
CC: Alexander Lobakin <aleksander.lobakin@...el.com>,
        Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Liam Girdwood
	<lgirdwood@...il.com>, Lukas Wunner <lukas@...ner.de>,
        Mark Brown
	<broonie@...nel.org>,
        Maíra Canal <mairacanal@...eup.net>,
        Robin Murphy <robin.murphy@....com>,
        Simona Vetter <simona.vetter@...ll.ch>, <linux-usb@...r.kernel.org>,
        <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] driver core: add a faux bus for use when a simple
 device/bus is needed

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;
> +}