linux-kernel - Re: [PATCH v2 02/10] sysfs: introduce callback attribute_group::bin

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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>,
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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