[SCSI] sysfs: make group is_valid return a mode_t

We have a problem in scsi_transport_spi in that we need to customise
not only the visibility of the attributes, but also their mode.  Fix
this by making the is_visible() callback return a mode, with 0
indicating is not visible.

Also add a sysfs_update_group() API to allow us to change either the
visibility or mode of the files at any time on the fly.

Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 03378e3..add3c5a 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -32,7 +32,7 @@
 
 struct attribute_group {
 	const char		*name;
-	int			(*is_visible)(struct kobject *,
+	mode_t			(*is_visible)(struct kobject *,
 					      struct attribute *, int);
 	struct attribute	**attrs;
 };
@@ -105,6 +105,8 @@
 
 int __must_check sysfs_create_group(struct kobject *kobj,
 				    const struct attribute_group *grp);
+int sysfs_update_group(struct kobject *kobj,
+		       const struct attribute_group *grp);
 void sysfs_remove_group(struct kobject *kobj,
 			const struct attribute_group *grp);
 int sysfs_add_file_to_group(struct kobject *kobj,