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

[Thomas Weißschuh]

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 <linux@xxxxxxxxxxxxxx>
---
 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