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Message-ID: <2024110726-hasty-obsolete-3780@gregkh>
Date: Thu, 7 Nov 2024 06:21:00 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Krzysztof Wilczyński <kw@...ux.com>
Cc: Thomas Weißschuh <linux@...ssschuh.net>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	Xinhui Pan <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
	Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
	Tudor Ambarus <tudor.ambarus@...aro.org>,
	Pratyush Yadav <pratyush@...nel.org>,
	Michael Walle <mwalle@...nel.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Richard Weinberger <richard@....at>,
	Vignesh Raghavendra <vigneshr@...com>,
	Naveen Krishna Chatradhi <naveenkrishna.chatradhi@....com>,
	Carlos Bilbao <carlos.bilbao.osdev@...il.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"David E. Box" <david.e.box@...ux.intel.com>,
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	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Richard Henderson <richard.henderson@...aro.org>,
	Matt Turner <mattst88@...il.com>,
	Frederic Barrat <fbarrat@...ux.ibm.com>,
	Andrew Donnellan <ajd@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>,
	Logan Gunthorpe <logang@...tatee.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-cxl@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
	linux-mtd@...ts.infradead.org, platform-driver-x86@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-usb@...r.kernel.org,
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Subject: Re: [PATCH v2 02/10] sysfs: introduce callback
 attribute_group::bin_size

On Thu, Nov 07, 2024 at 05:05:13AM +0900, Krzysztof Wilczyński wrote:
> Hello,
> 
> > Several drivers need to dynamically calculate the size of an binary
> > attribute. Currently this is done by assigning attr->size from the
> > is_bin_visible() callback.
> > 
> > This has drawbacks:
> > * It is not documented.
> > * A single attribute can be instantiated multiple times, overwriting the
> >   shared size field.
> > * It prevents the structure to be moved to read-only memory.
> > 
> > Introduce a new dedicated callback to calculate the size of the
> > attribute.
> 
> Would it be possible to have a helper that when run against a specific
> kobject reference, then it would refresh or re-run the size callbacks?
> 
> We have an use case where we resize BARs on demand via sysfs, and currently
> the only way to update the size of each resource sysfs object is to remove
> and added them again, which is a bit crude, and can also be unsafe.

How is it unsafe?

> Hence the question.
> 
> There exist the sysfs_update_groups(), but the BAR resource sysfs objects
> are currently, at least not yet, added to any attribute group.

then maybe they should be added to one :)

thanks,

greg k-h

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