From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from todd.t-8ch.de (todd.t-8ch.de [159.69.126.157]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 010C95CDF1; Tue, 4 Feb 2025 10:44:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=159.69.126.157 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738665886; cv=none; b=N2imcNEDu2rXrub0Wc13an7XROuyd42gLLTsKH/ejwN8I6rPD5uC9nibg0+ZOLpUwou5bLtdfqMG1xzmw7gpvnPtq0mMiLzuK2+P3OX6Htt/+r3NntGwcZ207UN8F8fR3WdNzrWv0uIIBp1ChzzYjByuOn7lENDuqQSCSBJT7Wc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738665886; c=relaxed/simple; bh=0i+/QpodIh9z8Ty+0nLpk/UyqlVHoGX8Wr8NdBoMgjg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dMfQonteWyppzGA/XlLB//Gw2wXs5gMKU1UjdcUcoOuUQln0FbmzWFNSt6GVsDlNxbfO6Q/06VYTaC8zxDrt03t0S7Hr0PKvVIVD0VOPeB6sWQcBAgNY9ETWjTmsBiytbdszxSzvvlD/KAb5DD6wg1rWl3mJqBSFAkE32X7TqbA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=weissschuh.net; spf=pass smtp.mailfrom=weissschuh.net; dkim=pass (1024-bit key) header.d=weissschuh.net header.i=@weissschuh.net header.b=S5xUWRQX; arc=none smtp.client-ip=159.69.126.157 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=weissschuh.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=weissschuh.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=weissschuh.net header.i=@weissschuh.net header.b="S5xUWRQX" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=weissschuh.net; s=mail; t=1738665881; bh=0i+/QpodIh9z8Ty+0nLpk/UyqlVHoGX8Wr8NdBoMgjg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=S5xUWRQXN71lENpIrHVtnAvrNCS4VqMu5RWX9xffByEjCxIoI7SHHHb9ayZYwcQPL bVBt1+DINDqOhR1miaQs9sWEMGI6OJ6eqJA5BIWz6Fv8tgudBBYDYL+LPtkjImZCay sIA6/QDGC+e3quoDTIqMliqQf5/eszvcaW8NDPrA= Date: Tue, 4 Feb 2025 11:44:41 +0100 From: Thomas =?utf-8?Q?Wei=C3=9Fschuh?= To: Greg Kroah-Hartman Cc: "Rafael J. Wysocki" , Danilo Krummrich , Lyude Paul , Alexander Lobakin , Andy Shevchenko , Bjorn Helgaas , Jonathan Cameron , Liam Girdwood , Lukas Wunner , Mark Brown , =?utf-8?B?TWHDrXJh?= Canal , Robin Murphy , Simona Vetter , Zijun Hu , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, rust-for-linux@vger.kernel.org Subject: Re: [PATCH 1/3] driver core: add a faux bus for use when a simple device/bus is needed Message-ID: <21fb6681-c214-4841-9cc6-45da3f965066@t-8ch.de> References: <2025020324-thermal-quilt-1bae@gregkh> <2025020326-backer-vendetta-7094@gregkh> <127f992b-1c53-49e1-8939-65b1d086fac5@t-8ch.de> <2025020430-polyester-unwind-5f9e@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2025020430-polyester-unwind-5f9e@gregkh> On 2025-02-04 11:20:43+0100, Greg Kroah-Hartman wrote: > On Tue, Feb 04, 2025 at 11:08:11AM +0100, Thomas Weißschuh wrote: > > On 2025-02-03 15:25:17+0100, Greg Kroah-Hartman wrote: > > > +static void faux_remove(struct device *dev) > > > +{ > > > + struct faux_object *faux_obj = to_faux_object(dev); > > > + struct faux_device *faux_dev = &faux_obj->faux_dev; > > > + const struct faux_driver_ops *faux_ops = faux_obj->faux_ops; > > > + > > > + if (faux_ops && faux_ops->remove) > > > + faux_ops->remove(faux_dev); > > > +} > > > + > > > +static const struct bus_type faux_bus_type = { > > > + .name = "faux_bus", > > > > Is the _bus suffix intentional? > > It was intentional. > > > Other busses don't have it. > > True. Naming is hard. I guess /sys/bus/faux/ makes sense, I will go > rename it. > > But for the "root" device, does /sys/devices/faux_bus/ make sense, or > should it be /sys/devices/faux/ as well? I'm now leaning toward the > latter... I'm leaning slightly towards the former. But my naming skills are beyond limited. > > > + .match = faux_match, > > > + .probe = faux_probe, > > > + .remove = faux_remove, > > > +}; > > > + > > > +static void faux_device_release(struct device *dev) > > > +{ > > > + struct faux_object *faux_obj = to_faux_object(dev); > > > + struct device_driver *drv = &faux_obj->driver; > > > + > > > + /* > > > + * Now that the device is going away, it has been unbound from the > > > + * driver we created for it, so it is safe to unregister the driver from > > > + * the system. > > > + */ > > > + driver_unregister(drv); > > > + > > > + kfree(faux_obj); > > > +} > > > + > > > +/** > > > + * __faux_device_create - create and register a faux device and driver > > > + * @name: name of the device and driver we are adding > > > + * @faux_ops: struct faux_driver_ops that the new device will call back into, can be NULL > > > + * @owner: module owner of the device/driver > > > + * > > > + * Create a new faux device and driver, both with the same name, and register > > > + * them in the driver core properly. The probe() callback of @faux_ops will be > > > + * called with the new device that is created for the caller to do something > > > + * with. > > > + */ > > > +struct faux_device *__faux_device_create(const char *name, > > > + struct faux_driver_ops *faux_ops, > > > > const > > > > > + struct module *owner) > > > > What about attributes? > > What in-kernel user of this wants an attribute for such a device? It was mostly a guess. However drivers/video/fbdev/gbefb.c seems to be an example. > And again, if we find one, we can make a faux_device_create_groups() > call that takes a pointer to an attribute group structure if it's really > needed. Fair enough. > > > +{ > > > + struct device_driver *drv; > > > + struct device *dev; > > > + struct faux_object *faux_obj; > > > + struct faux_device *faux_dev; > > > + int ret; > > > + > > > + faux_obj = kzalloc(sizeof(*faux_obj) + strlen(name) + 1, GFP_KERNEL); > > > + if (!faux_obj) > > > + return NULL; > > > + > > > + /* Save off the name of the object into local memory */ > > > + strcpy(faux_obj->name, name); > > > + > > > + /* Initialize the driver portion and register it with the driver core */ > > > + faux_obj->faux_ops = faux_ops; > > > + drv = &faux_obj->driver; > > > + > > > + drv->owner = owner; > > > + drv->name = faux_obj->name; > > > > Assuming most names are constant, this would be better with kstrdup_const(). > > Which is also used by dev_set_name() under the hood. > > I've now removed the additional driver, but note that this is just a > pointer assignment, which is fine to do here as the lifespan of > faux_obj->name outlived the driver structure's lifespan. It outlives it because there is extra space allocated for it in faux_obj. With kstrdup_const() that space would not be needed. In the end it shouldn't really matter one way or another. Thomas