rust: configfs: use core::ffi::CStr method names

Prepare for `core::ffi::CStr` taking the place of `kernel::str::CStr` by
avoid methods that only exist on the latter.

Also avoid `Deref<Target=BStr> for CStr` as that impl doesn't exist on
`core::ffi::CStr`.

Link: #1075
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Acked-by: Andreas Hindborg <a.hindborg@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: tamird

rust/kernel/configfs.rs

@@ -263,7 +263,7 @@ impl<Data> Group<Data> {
         try_pin_init!(Self {
             group <- pin_init::init_zeroed().chain(|v: &mut Opaque<bindings::config_group>| {
                 let place = v.get();
-                let name = name.as_bytes_with_nul().as_ptr();
+                let name = name.to_bytes_with_nul().as_ptr();
                 // SAFETY: It is safe to initialize a group once it has been zeroed.
                 unsafe {
                     bindings::config_group_init_type_name(place, name.cast(), item_type.as_ptr())
@@ -613,7 +613,7 @@ where
     pub const fn new(name: &'static CStr) -> Self {
         Self {
             attribute: Opaque::new(bindings::configfs_attribute {
-                ca_name: name.as_char_ptr(),
+                ca_name: crate::str::as_char_ptr_in_const_context(name),
                 ca_owner: core::ptr::null_mut(),
                 ca_mode: 0o660,
                 show: Some(Self::show),

samples/rust/rust_configfs.rs

@@ -94,7 +94,7 @@ impl configfs::AttributeOperations<0> for Configuration {
 
     fn show(container: &Configuration, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
         pr_info!("Show message\n");
-        let data = container.message;
+        let data = container.message.to_bytes();
         page[0..data.len()].copy_from_slice(data);
         Ok(data.len())
     }