linux-kernel - Re: [PATCH v3 1/7] sysfs: attribute_group: allow registration of const attribute

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Message-ID: <2025081953-canteen-criteria-c604@gregkh>
Date: Tue, 19 Aug 2025 16:10:42 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] sysfs: attribute_group: allow registration of
 const attribute

On Tue, Aug 19, 2025 at 03:59:04PM +0200, Thomas Weißschuh wrote:
> On 2025-08-19 13:22:55+0200, Greg Kroah-Hartman wrote:
> > On Mon, Aug 11, 2025 at 11:14:27AM +0200, Thomas Weißschuh wrote:
> > > To be able to constify instances of struct attribute it has to be
> > > possible to add them to struct attribute_group.
> > > The current type of the attrs member however is not compatible with that.
> > > Introduce a union that allows registration of both const and non-const
> > > attributes to enable a piecewise transition.
> > > As both union member types are compatible no logic needs to be adapted.
> > > 
> > > Technically it is now possible register a const struct
> > > attribute and receive it as mutable pointer in the callbacks.
> > > This is a soundness issue.
> > > But this same soundness issue already exists today in
> > > sysfs_create_file().
> > > Also the struct definition and callback implementation are always
> > > closely linked and are meant to be moved to const in lockstep.
> > > 
> > > Similar to commit 906c508afdca ("sysfs: attribute_group: allow registration of const bin_attribute")
> > > 
> > > Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> > > ---
> > >  include/linux/sysfs.h | 5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
> > > index f418aae4f1134f8126783d9e8eb575ba4278e927..a47092e837d9eb014894d1f7e49f0fd0f9a2e350 100644
> > > --- a/include/linux/sysfs.h
> > > +++ b/include/linux/sysfs.h
> > > @@ -105,7 +105,10 @@ struct attribute_group {
> > >  	size_t			(*bin_size)(struct kobject *,
> > >  					    const struct bin_attribute *,
> > >  					    int);
> > > -	struct attribute	**attrs;
> > > +	union {
> > > +		struct attribute	**attrs;
> > > +		const struct attribute	*const *attrs_new;
> > 
> > I know you will drop the "_new" prefix after a while, but "new" is
> > relative, and not very descriptive.
> 
> That is somewhat intentional to express that it is a transitional thing.

Fair, but given the huge quantity here, it's going to take a long time,
so "new" is going to be rough to push through for 6+ months.

> > How about "_const"?
> 
> At some point the regular variant will be const too, so "_const" would
> be a bit weird.

Yes, that's when you "switch it back", right?  You would have to do that
for _new as well.

thanks,

greg k-h