[PATCH 5/6] configfs: Allow the registration of const struct configfs_attribute

The attribute structure defined in driver code never need to be
modified. Allow them to be marked as const.

As there are many drivers which use these attributes, prepare for a
phased transition by using a union of const and non-const attributes.

After all drivers have been migrated to the const variant, the non-const
one can be replaced by the const one and the transition machinery will
be removed again.

Signed-off-by: Thomas Weißschuh <[email protected]>
---
 fs/configfs/dir.c        | 4 ++--
 include/linux/configfs.h | 5 ++++-
 rust/kernel/configfs.rs  | 8 ++++++--
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 9a5c2bc4065d..c2152288517c 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -632,8 +632,8 @@ static int populate_attrs(struct config_item *item)
 
 	ops = t->ct_group_ops;
 
-	if (t->ct_attrs) {
-		for (i = 0; (attr = t->ct_attrs[i]) != NULL; i++) {
+	if (t->ct_attrs_const) {
+		for (i = 0; (attr = t->ct_attrs_const[i]) != NULL; i++) {
 			if (ops && ops->is_visible && !ops->is_visible(item, attr, i))
 				continue;
 
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index eff2fb22ab70..5bead9173ec1 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -66,7 +66,10 @@ struct config_item_type {
 	struct module				*ct_owner;
 	const struct configfs_item_operations	*ct_item_ops;
 	const struct configfs_group_operations	*ct_group_ops;
-	struct configfs_attribute		**ct_attrs;
+	union {
+		struct configfs_attribute		**ct_attrs;
+		const struct configfs_attribute		*const *ct_attrs_const;
+	};
 	const struct configfs_bin_attribute	*const *ct_bin_attrs;
 };
 
diff --git a/rust/kernel/configfs.rs b/rust/kernel/configfs.rs
index f99a6e376fa3..2ef9cce693b9 100644
--- a/rust/kernel/configfs.rs
+++ b/rust/kernel/configfs.rs
@@ -756,7 +756,9 @@ pub const fn new_with_child_ctor<const N: usize, Child>(
                         ct_owner: owner.as_ptr(),
                         ct_group_ops: GroupOperationsVTable::<Data, Child>::vtable_ptr(),
                         ct_item_ops: ItemOperationsVTable::<$tpe, Data>::vtable_ptr(),
-                        ct_attrs: core::ptr::from_ref(attributes).cast_mut().cast(),
+                        __bindgen_anon_1: bindings::config_item_type__bindgen_ty_1 {
+                            ct_attrs_const: core::ptr::from_ref(attributes).cast(),
+                        },
                         ct_bin_attrs: core::ptr::null(),
                     }),
                     _p: PhantomData,
@@ -773,7 +775,9 @@ pub const fn new<const N: usize>(
                         ct_owner: owner.as_ptr(),
                         ct_group_ops: core::ptr::null(),
                         ct_item_ops: ItemOperationsVTable::<$tpe, Data>::vtable_ptr(),
-                        ct_attrs: core::ptr::from_ref(attributes).cast_mut().cast(),
+                        __bindgen_anon_1: bindings::config_item_type__bindgen_ty_1 {
+                            ct_attrs_const: core::ptr::from_ref(attributes).cast(),
+                        },
                         ct_bin_attrs: core::ptr::null(),
                     }),
                     _p: PhantomData,

-- 
2.55.0