sysfs: attribute_group: enable const variants of is_visible()

When constifying instances of struct attribute, for consistency the
corresponding .is_visible() callback should be adapted, too.
Introduce a temporary transition mechanism until all callbacks are
converted.

Signed-off-by: Thomas Weißschuh <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

fs/sysfs/group.c

···
 	if (grp->attrs && grp->attrs[0] && grp->is_visible)
 		return grp->is_visible(kobj, grp->attrs[0], 0);
 
+	if (grp->attrs && grp->attrs[0] && grp->is_visible_const)
+		return grp->is_visible_const(kobj, grp->attrs[0], 0);
+
 	if (grp->bin_attrs && grp->bin_attrs[0] && grp->is_bin_visible)
 		return grp->is_bin_visible(kobj, grp->bin_attrs[0], 0);
 
···
 			 */
 			if (update)
 				kernfs_remove_by_name(parent, (*attr)->name);
-			if (grp->is_visible) {
-				mode = grp->is_visible(kobj, *attr, i);
+			if (grp->is_visible || grp->is_visible_const) {
+				if (grp->is_visible)
+					mode = grp->is_visible(kobj, *attr, i);
+				else
+					mode = grp->is_visible_const(kobj, *attr, i);
 				mode &= ~SYSFS_GROUP_INVISIBLE;
 				if (!mode)
 					continue;

include/linux/sysfs.h

···
  */
 struct attribute_group {
 	const char		*name;
-	umode_t			(*is_visible)(struct kobject *,
-					      struct attribute *, int);
+	__SYSFS_FUNCTION_ALTERNATIVE(
+		umode_t			(*is_visible)(struct kobject *,
+						      struct attribute *, int);
+		umode_t			(*is_visible_const)(struct kobject *,
+							    const struct attribute *, int);
+	);
 	umode_t			(*is_bin_visible)(struct kobject *,
 						  const struct bin_attribute *, int);
 	size_t			(*bin_size)(struct kobject *,