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

["Thomas Weißschuh" <linux@weissschuh.net>]

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@weissschuh.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.

> How about "_const"?

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

> > +	};
> >  	union {
> >  		const struct bin_attribute	*const *bin_attrs;
> >  		const struct bin_attribute	*const *bin_attrs_new;
> 
> There is no bin_attrs_new anymore.  Finally.  sorry about that...

Thanks! No worries.


Thomas