linux-kernel - Re: [PATCH v3 5/7] samples/kobject: add is

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Message-ID: <d57603c6-d7cf-4d37-aaaa-6bad477075d6@t-8ch.de>
Date: Tue, 19 Aug 2025 16:00:29 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 5/7] samples/kobject: add is_visible() callback to
 attribute group

On 2025-08-19 13:24:04+0200, Greg Kroah-Hartman wrote:
> On Mon, Aug 11, 2025 at 11:14:31AM +0200, Thomas Weißschuh wrote:
> > There was no example for the is_visible() callback so far.
> > 
> > It will also become an example and test for the constification of
> > 'struct attribute' later.
> > 
> > Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> > ---
> >  samples/kobject/kset-example.c | 17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> > 
> > diff --git a/samples/kobject/kset-example.c b/samples/kobject/kset-example.c
> > index 579ce150217c6e613887e32a08206573543b3091..1aac595ed9498b30448485a60d9376cb5b5ea1d3 100644
> > --- a/samples/kobject/kset-example.c
> > +++ b/samples/kobject/kset-example.c
> > @@ -178,7 +178,22 @@ static struct attribute *foo_default_attrs[] = {
> >  	&bar_attribute.attr,
> >  	NULL,	/* need to NULL terminate the list of attributes */
> >  };
> > -ATTRIBUTE_GROUPS(foo_default);
> > +
> > +static umode_t foo_default_attrs_is_visible(struct kobject *kobj,
> > +					    struct attribute *attr,
> > +					    int n)
> > +{
> > +	/* Hide attributes with the same name as the kobject. */
> > +	if (strcmp(kobject_name(kobj), attr->name) == 0)
> > +		return 0;
> > +	return attr->mode;
> > +}
> > +
> > +static const struct attribute_group foo_default_group = {
> > +	.attrs		= foo_default_attrs,
> > +	.is_visible	= foo_default_attrs_is_visible,
> > +};
> > +__ATTRIBUTE_GROUPS(foo_default);
> 
> Wait, why?  Shouldn't ATTRIBUTE_GROUPS() still work here?  No one should
> have to call __ATTRIBUTE_GROUPS() in their code, that's just going to be
> too messy over time.

ATTRIBUTE_GROUPS() can not handle .is_visible().
There are already a few users throughout the tree.

Thomas