linux-kernel - Re: [PATCH 1/6] sysfs: attribute_group: allow registration of const attribute

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Message-ID: <3d4c063e-e56d-466c-a3a7-58566bf1da3c@t-8ch.de>
Date: Sat, 28 Jun 2025 10:19:07 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org, 
	Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH 1/6] sysfs: attribute_group: allow registration of const
 attribute

Hi Greg,

On 2025-01-17 08:01:00+0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 16, 2025 at 06:32:27PM +0100, 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 0f2fcd244523f050c5286f19d4fe1846506f9214..f5e25bed777a6a6e717f10973f1abcd12111f5c5 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'm all for the idea, BUT, let's finish up doing this one:
> 
> >  	union {
> >  		struct bin_attribute		**bin_attrs;
> >  		const struct bin_attribute	*const *bin_attrs_new;
> 
> first please.
> 
> That way we can see just how "easy" the switch from _new to not-new goes :)

I'd like to resend these preparatory patches so they go into v6.17-rc1
and I can work on the follow-up changes.
In my opinion the switch from _new will work nicely. There have been no
new users of _new in -next at all.

Any objections?


Thomas