[PATCH v15 0/4] rust: replace kernel::str::CStr w/ core::ffi::CStr

[PATCH v15 0/4] rust: replace kernel::str::CStr w/ core::ffi::CStr

[Tamir Duberstein]

This picks up from Michal Rostecki's work[0]. Per Michal's guidance I
have omitted Co-authored tags, as the end result is quite different.

This series is intended to be taken through rust-next. The final patch
in the series requires some other subsystems' `Acked-by`s:
- rust/kernel/device.rs: driver-core. Already acked by gregkh.
- rust/kernel/firmware.rs: driver-core. Danilo, could you take a look?
- rust/kernel/seq_file.rs: vfs, I think? missing MAINTAINERS entry.
  Christian Brauner <brauner@kernel.org>, perhaps?
- rust/kernel/sync/*: no clear owner, probably doesn't need any.

This series depends on steps 2a[1] and 2b[2] which both depend on step
1[3].

Link: https://lore.kernel.org/rust-for-linux/20240819153656.28807-2-vadorovsky@protonmail.com/t/#u [0]
Link: https://lore.kernel.org/all/20250709-core-cstr-fanout-1-v1-0-64308e7203fc@gmail.com/ [1]
Link: https://lore.kernel.org/all/20250709-core-cstr-fanout-1-v1-0-fd793b3e58a2@gmail.com/ [2]
Link: https://lore.kernel.org/all/20250704-core-cstr-prepare-v1-0-a91524037783@gmail.com/ [3]
Closes: https://github.com/Rust-for-Linux/linux/issues/1075

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
Changes in v15:
- Seal `CStrExt`. (Benno Lossin)
- Add patch to remove trailing commas from
  samples/rust/rust_driver_platform.rs.
- Link to v14: https://lore.kernel.org/r/20250710-cstr-core-v14-0-ca7e0ca82c82@gmail.com

Changes in v14:
- Break the change into multiple series.
- Move `CStr` reexport to `kernel::ffi`. (Alice Ryhl)
- `pub use core::fmt::{....}` in `kernel/fmt.rs`. (Benno Lossin)
- Avoid unnecessary binding to `first_lit` in `fmt!`. (Benno Lossin)
- Add comment to `identifier`-extracting loop. (Benno Lossin)
- Change `quote_spanned!` formatting. (Benno Lossin)
- Link to v13: https://lore.kernel.org/r/20250701-cstr-core-v13-0-29f7d3eb97a6@gmail.com

Changes in v13:
- Rebase on v6.16-rc4.
- Link to v12: https://lore.kernel.org/r/20250619-cstr-core-v12-0-80c9c7b45900@gmail.com

Changes in v12:
- Introduce `kernel::fmt::Display` to allow implementations on foreign
  types.
- Tidy up doc comment on `str_to_cstr`. (Alice Ryhl).
- Link to v11: https://lore.kernel.org/r/20250530-cstr-core-v11-0-cd9c0cbcb902@gmail.com

Changes in v11:
- Use `quote_spanned!` to avoid `use<'a, T>` and generally reduce manual
  token construction.
- Add a commit to simplify `quote_spanned!`.
- Drop first commit in favor of
  https://lore.kernel.org/rust-for-linux/20240906164448.2268368-1-paddymills@proton.me/.
  (Miguel Ojeda)
- Correctly handle expressions such as `pr_info!("{a}", a = a = a)`.
  (Benno Lossin)
- Avoid dealing with `}}` escapes, which is not needed. (Benno Lossin)
- Revert some unnecessary changes. (Benno Lossin)
- Rename `c_str_avoid_literals!` to `str_to_cstr!`. (Benno Lossin &
  Alice Ryhl).
- Link to v10: https://lore.kernel.org/r/20250524-cstr-core-v10-0-6412a94d9d75@gmail.com

Changes in v10:
- Rebase on cbeaa41dfe26b72639141e87183cb23e00d4b0dd.
- Implement Alice's suggestion to use a proc macro to work around orphan
  rules otherwise preventing `core::ffi::CStr` to be directly printed
  with `{}`.
- Link to v9: https://lore.kernel.org/r/20250317-cstr-core-v9-0-51d6cc522f62@gmail.com

Changes in v9:
- Rebase on rust-next.
- Restore `impl Display for BStr` which exists upstream[1].
- Link: https://doc.rust-lang.org/nightly/std/bstr/struct.ByteStr.html#impl-Display-for-ByteStr [1]
- Link to v8: https://lore.kernel.org/r/20250203-cstr-core-v8-0-cb3f26e78686@gmail.com

Changes in v8:
- Move `{from,as}_char_ptr` back to `CStrExt`. This reduces the diff
  some.
- Restore `from_bytes_with_nul_unchecked_mut`, `to_cstring`.
- Link to v7: https://lore.kernel.org/r/20250202-cstr-core-v7-0-da1802520438@gmail.com

Changes in v7:
- Rebased on mainline.
- Restore functionality added in commit a321f3ad0a5d ("rust: str: add
  {make,to}_{upper,lower}case() to CString").
- Used `diff.algorithm patience` to improve diff readability.
- Link to v6: https://lore.kernel.org/r/20250202-cstr-core-v6-0-8469cd6d29fd@gmail.com

Changes in v6:
- Split the work into several commits for ease of review.
- Restore `{from,as}_char_ptr` to allow building on ARM (see commit
  message).
- Add `CStrExt` to `kernel::prelude`. (Alice Ryhl)
- Remove `CStrExt::from_bytes_with_nul_unchecked_mut` and restore
  `DerefMut for CString`. (Alice Ryhl)
- Rename and hide `kernel::c_str!` to encourage use of C-String
  literals.
- Drop implementation and invocation changes in kunit.rs. (Trevor Gross)
- Drop docs on `Display` impl. (Trevor Gross)
- Rewrite docs in the style of the standard library.
- Restore the `test_cstr_debug` unit tests to demonstrate that the
  implementation has changed.

Changes in v5:
- Keep the `test_cstr_display*` unit tests.

Changes in v4:
- Provide the `CStrExt` trait with `display()` method, which returns a
   `CStrDisplay` wrapper with `Display` implementation. This addresses
   the lack of `Display` implementation for `core::ffi::CStr`.
- Provide `from_bytes_with_nul_unchecked_mut()` method in `CStrExt`,
   which might be useful and is going to prevent manual, unsafe casts.
- Fix a typo (s/preffered/prefered/).

Changes in v3:
- Fix the commit message.
- Remove redundant braces in `use`, when only one item is imported.

Changes in v2:
- Do not remove `c_str` macro. While it's preferred to use C-string
   literals, there are two cases where `c_str` is helpful:
   - When working with macros, which already return a Rust string literal
     (e.g. `stringify!`).
   - When building macros, where we want to take a Rust string literal as an
     argument (for caller's convenience), but still use it as a C-string
     internally.
- Use Rust literals as arguments in macros (`new_mutex`, `new_condvar`,
   `new_mutex`). Use the `c_str` macro to convert these literals to C-string
   literals.
- Use `c_str` in kunit.rs for converting the output of `stringify!` to a
   `CStr`.
- Remove `DerefMut` implementation for `CString`.

---
Tamir Duberstein (4):
      rust: macros: reduce collections in `quote!` macro
      samples: rust: platform: remove trailing commas
      rust: support formatting of foreign types
      rust: replace `CStr` with `core::ffi::CStr`

 rust/ffi.rs                          |   2 +
 rust/kernel/device.rs                |   1 +
 rust/kernel/error.rs                 |   2 +
 rust/kernel/firmware.rs              |   9 +-
 rust/kernel/fmt.rs                   |  87 +++++++-
 rust/kernel/prelude.rs               |   7 +-
 rust/kernel/seq_file.rs              |   2 +-
 rust/kernel/str.rs                   | 395 ++++++++---------------------------
 rust/kernel/sync/condvar.rs          |   2 +-
 rust/kernel/sync/lock.rs             |   2 +-
 rust/kernel/sync/lock/global.rs      |   2 +-
 rust/macros/fmt.rs                   |  94 +++++++++
 rust/macros/lib.rs                   |  19 ++
 rust/macros/quote.rs                 | 111 +++++-----
 samples/rust/rust_driver_platform.rs |   4 +-
 15 files changed, 367 insertions(+), 372 deletions(-)
---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20250201-cstr-core-d4b9b69120cf
prerequisite-message-id: 20250813-core-cstr-fanout-1-v3-0-545c14bc44ff@gmail.com
prerequisite-patch-id: 0ccc3545ff9bf22a67b79a944705cef2fb9c2bbf
prerequisite-patch-id: b1866166714606d5c11a4d7506abe4c2f86dac8d
prerequisite-patch-id: b575ae9ef33020b691c8c5a17bd1985676519e14
prerequisite-patch-id: 8fee5e2daf0749362331dad4fc63d907a01b14e9
prerequisite-patch-id: 366ef1f93fb40b1d039768f2041ff79995e7e228
prerequisite-patch-id: 1d350291f9292f910081856d8f7d5e4d9545cfd1
prerequisite-patch-id: 9a6a60bd2b209126de64c16a77a3a1d229dd898c
prerequisite-patch-id: 08ae5855768ec3b4c68272b86d2a0e0667c9aa47
prerequisite-patch-id: 801be981c2346617fa9412498930b68dc784693b
prerequisite-patch-id: f0dbf0a55a27fe8e199e242d1f79ea800d1ddb66
prerequisite-patch-id: c0b4abb4d44f7e63d002d0bfe5239296930c183e
prerequisite-message-id: 20250813-core-cstr-fanout-1-v3-0-a15eca059c51@gmail.com
prerequisite-patch-id: 6711f2a2f25c12784057aa725a9482feef6bb6f0
prerequisite-patch-id: 3b5144133c0e239e0a258c9aa4da0df2dd464e66
prerequisite-patch-id: 589a352ba7f7c9aefefd84dfd3b6b20e290b0d14
prerequisite-patch-id: 2a4b0b9170e25637b9eba0e516863bdcdb4149a8
prerequisite-patch-id: 3d89601bba1fb01d190b0ba415b28ad9cbf1e209
prerequisite-patch-id: 10923aebf24011b727f60496c0f9e0ad57e0a967
prerequisite-patch-id: 9a7e8ba460358985147efd347658be31fbc78ba2
prerequisite-patch-id: f79b8755f3d75effc581d09eafe5725043516aad
prerequisite-patch-id: d598958c2d64dcb56a5cd64b088594be51b1d752

Best regards,
--  
Tamir Duberstein <tamird@gmail.com>

[PATCH v15 1/4] rust: macros: reduce collections in `quote!` macro

[Tamir Duberstein]

Remove a handful of unncessary intermediate vectors and token streams;
mainly the top-level stream can be directly extended with the notable
exception of groups.

Remove an unnecessary `#[allow(dead_code)]` added in commit dbd5058ba60c
("rust: make pin-init its own crate").

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 rust/macros/quote.rs | 104 ++++++++++++++++++++++++---------------------------
 1 file changed, 49 insertions(+), 55 deletions(-)

diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs
index 92cacc4067c9..acc140c18653 100644
--- a/rust/macros/quote.rs
+++ b/rust/macros/quote.rs
@@ -2,7 +2,6 @@
 
 use proc_macro::{TokenStream, TokenTree};
 
-#[allow(dead_code)]
 pub(crate) trait ToTokens {
     fn to_tokens(&self, tokens: &mut TokenStream);
 }
@@ -47,121 +46,116 @@ fn to_tokens(&self, tokens: &mut TokenStream) {
 /// `quote` crate but provides only just enough functionality needed by the current `macros` crate.
 macro_rules! quote_spanned {
     ($span:expr => $($tt:tt)*) => {{
-        let mut tokens: ::std::vec::Vec<::proc_macro::TokenTree>;
-        #[allow(clippy::vec_init_then_push)]
+        let mut tokens = ::proc_macro::TokenStream::new();
         {
-            tokens = ::std::vec::Vec::new();
             let span = $span;
             quote_spanned!(@proc tokens span $($tt)*);
         }
-        ::proc_macro::TokenStream::from_iter(tokens)
+        tokens
     }};
     (@proc $v:ident $span:ident) => {};
     (@proc $v:ident $span:ident #$id:ident $($tt:tt)*) => {
-        let mut ts = ::proc_macro::TokenStream::new();
-        $crate::quote::ToTokens::to_tokens(&$id, &mut ts);
-        $v.extend(ts);
+        $crate::quote::ToTokens::to_tokens(&$id, &mut $v);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident #(#$id:ident)* $($tt:tt)*) => {
         for token in $id {
-            let mut ts = ::proc_macro::TokenStream::new();
-            $crate::quote::ToTokens::to_tokens(&token, &mut ts);
-            $v.extend(ts);
+            $crate::quote::ToTokens::to_tokens(&token, &mut $v);
         }
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident ( $($inner:tt)* ) $($tt:tt)*) => {
         #[allow(unused_mut)]
-        let mut tokens = ::std::vec::Vec::<::proc_macro::TokenTree>::new();
+        let mut tokens = ::proc_macro::TokenStream::new();
         quote_spanned!(@proc tokens $span $($inner)*);
-        $v.push(::proc_macro::TokenTree::Group(::proc_macro::Group::new(
+        $v.extend([::proc_macro::TokenTree::Group(::proc_macro::Group::new(
             ::proc_macro::Delimiter::Parenthesis,
-            ::proc_macro::TokenStream::from_iter(tokens)
-        )));
+            tokens,
+        ))]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident [ $($inner:tt)* ] $($tt:tt)*) => {
-        let mut tokens = ::std::vec::Vec::new();
+        let mut tokens = ::proc_macro::TokenStream::new();
         quote_spanned!(@proc tokens $span $($inner)*);
-        $v.push(::proc_macro::TokenTree::Group(::proc_macro::Group::new(
+        $v.extend([::proc_macro::TokenTree::Group(::proc_macro::Group::new(
             ::proc_macro::Delimiter::Bracket,
-            ::proc_macro::TokenStream::from_iter(tokens)
-        )));
+            tokens,
+        ))]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident { $($inner:tt)* } $($tt:tt)*) => {
-        let mut tokens = ::std::vec::Vec::new();
+        let mut tokens = ::proc_macro::TokenStream::new();
         quote_spanned!(@proc tokens $span $($inner)*);
-        $v.push(::proc_macro::TokenTree::Group(::proc_macro::Group::new(
+        $v.extend([::proc_macro::TokenTree::Group(::proc_macro::Group::new(
             ::proc_macro::Delimiter::Brace,
-            ::proc_macro::TokenStream::from_iter(tokens)
-        )));
+            tokens,
+        ))]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident :: $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new(':', ::proc_macro::Spacing::Joint)
-        ));
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new(':', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::Spacing::Joint, ::proc_macro::Spacing::Alone].map(|spacing| {
+            ::proc_macro::TokenTree::Punct(::proc_macro::Punct::new(':', spacing))
+        }));
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident : $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new(':', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new(':', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident , $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new(',', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new(',', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident @ $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new('@', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('@', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident ! $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new('!', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('!', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident ; $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new(';', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new(';', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident + $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new('+', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('+', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident = $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new('=', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('=', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident # $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Punct(
-                ::proc_macro::Punct::new('#', ::proc_macro::Spacing::Alone)
-        ));
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('#', ::proc_macro::Spacing::Alone),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident _ $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Ident(::proc_macro::Ident::new("_", $span)));
+        $v.extend([::proc_macro::TokenTree::Ident(
+            ::proc_macro::Ident::new("_", $span),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
     (@proc $v:ident $span:ident $id:ident $($tt:tt)*) => {
-        $v.push(::proc_macro::TokenTree::Ident(::proc_macro::Ident::new(stringify!($id), $span)));
+        $v.extend([::proc_macro::TokenTree::Ident(
+            ::proc_macro::Ident::new(stringify!($id), $span),
+        )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
 }

-- 
2.50.1

[PATCH v15 2/4] samples: rust: platform: remove trailing commas

[Tamir Duberstein]

This prepares for the next commit in which we introduce a custom
formatting macro; that macro doesn't handle these spurious commas, so
just remove them.

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 samples/rust/rust_driver_platform.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/samples/rust/rust_driver_platform.rs b/samples/rust/rust_driver_platform.rs
index 69ed55b7b0fa..ad08df0d73f0 100644
--- a/samples/rust/rust_driver_platform.rs
+++ b/samples/rust/rust_driver_platform.rs
@@ -146,7 +146,7 @@ fn properties_parse(dev: &device::Device) -> Result {
 
         let name = c_str!("test,u32-optional-prop");
         let prop = fwnode.property_read::<u32>(name).or(0x12);
-        dev_info!(dev, "'{name}'='{prop:#x}' (default = 0x12)\n",);
+        dev_info!(dev, "'{name}'='{prop:#x}' (default = 0x12)\n");
 
         // A missing required property will print an error. Discard the error to
         // prevent properties_parse from failing in that case.
@@ -161,7 +161,7 @@ fn properties_parse(dev: &device::Device) -> Result {
         let prop: [i16; 4] = fwnode.property_read(name).required_by(dev)?;
         dev_info!(dev, "'{name}'='{prop:?}'\n");
         let len = fwnode.property_count_elem::<u16>(name)?;
-        dev_info!(dev, "'{name}' length is {len}\n",);
+        dev_info!(dev, "'{name}' length is {len}\n");
 
         let name = c_str!("test,i16-array");
         let prop: KVec<i16> = fwnode.property_read_array_vec(name, 4)?.required_by(dev)?;

-- 
2.50.1

[PATCH v15 3/4] rust: support formatting of foreign types

[Tamir Duberstein]

Introduce a `fmt!` macro which wraps all arguments in
`kernel::fmt::Adapter` and a `kernel::fmt::Display` trait. This enables
formatting of foreign types (like `core::ffi::CStr`) that do not
implement `core::fmt::Display` due to concerns around lossy conversions
which do not apply in the kernel.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Custom.20formatting/with/516476467
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 rust/kernel/fmt.rs     | 87 +++++++++++++++++++++++++++++++++++++++++++++-
 rust/kernel/prelude.rs |  3 +-
 rust/macros/fmt.rs     | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/macros/lib.rs     | 19 ++++++++++
 rust/macros/quote.rs   |  7 ++++
 5 files changed, 207 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/fmt.rs b/rust/kernel/fmt.rs
index 0306e8388968..84d634201d90 100644
--- a/rust/kernel/fmt.rs
+++ b/rust/kernel/fmt.rs
@@ -4,4 +4,89 @@
 //!
 //! This module is intended to be used in place of `core::fmt` in kernel code.
 
-pub use core::fmt::{Arguments, Debug, Display, Error, Formatter, Result, Write};
+pub use core::fmt::{Arguments, Debug, Error, Formatter, Result, Write};
+
+/// Internal adapter used to route allow implementations of formatting traits for foreign types.
+///
+/// It is inserted automatically by the [`fmt!`] macro and is not meant to be used directly.
+///
+/// [`fmt!`]: crate::prelude::fmt!
+#[doc(hidden)]
+pub struct Adapter<T>(pub T);
+
+macro_rules! impl_fmt_adapter_forward {
+    ($($trait:ident),* $(,)?) => {
+        $(
+            impl<T: $trait> $trait for Adapter<T> {
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    let Self(t) = self;
+                    $trait::fmt(t, f)
+                }
+            }
+        )*
+    };
+}
+
+use core::fmt::{Binary, LowerExp, LowerHex, Octal, Pointer, UpperExp, UpperHex};
+impl_fmt_adapter_forward!(Debug, LowerHex, UpperHex, Octal, Binary, Pointer, LowerExp, UpperExp);
+
+/// A copy of [`core::fmt::Display`] that allows us to implement it for foreign types.
+///
+/// Types should implement this trait rather than [`core::fmt::Display`]. Together with the
+/// [`Adapter`] type and [`fmt!`] macro, it allows for formatting foreign types (e.g. types from
+/// core) which do not implement [`core::fmt::Display`] directly.
+///
+/// [`fmt!`]: crate::prelude::fmt!
+pub trait Display {
+    /// Same as [`core::fmt::Display::fmt`].
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result;
+}
+
+impl<T: ?Sized + Display> Display for &T {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        Display::fmt(*self, f)
+    }
+}
+
+impl<T: ?Sized + Display> core::fmt::Display for Adapter<&T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        let Self(t) = self;
+        Display::fmt(t, f)
+    }
+}
+
+macro_rules! impl_display_forward {
+    ($(
+        $( { $($generics:tt)* } )? $ty:ty $( { where $($where:tt)* } )?
+    ),* $(,)?) => {
+        $(
+            impl$($($generics)*)? Display for $ty $(where $($where)*)? {
+                fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+                    core::fmt::Display::fmt(self, f)
+                }
+            }
+        )*
+    };
+}
+
+impl_display_forward!(
+    bool,
+    char,
+    core::panic::PanicInfo<'_>,
+    Arguments<'_>,
+    i128,
+    i16,
+    i32,
+    i64,
+    i8,
+    isize,
+    str,
+    u128,
+    u16,
+    u32,
+    u64,
+    u8,
+    usize,
+    {<T: ?Sized>} crate::sync::Arc<T> {where crate::sync::Arc<T>: core::fmt::Display},
+    {<T: ?Sized>} crate::sync::UniqueArc<T> {where crate::sync::UniqueArc<T>: core::fmt::Display},
+);
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 25fe97aafd02..f009f198f593 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -22,7 +22,7 @@
 pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec, Vec};
 
 #[doc(no_inline)]
-pub use macros::{export, kunit_tests, module, vtable};
+pub use macros::{export, fmt, kunit_tests, module, vtable};
 
 pub use pin_init::{init, pin_data, pin_init, pinned_drop, InPlaceWrite, Init, PinInit, Zeroable};
 
@@ -33,7 +33,6 @@
 pub use super::dbg;
 pub use super::{dev_alert, dev_crit, dev_dbg, dev_emerg, dev_err, dev_info, dev_notice, dev_warn};
 pub use super::{pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
-pub use core::format_args as fmt;
 
 pub use super::{try_init, try_pin_init};
 
diff --git a/rust/macros/fmt.rs b/rust/macros/fmt.rs
new file mode 100644
index 000000000000..2f4b9f6e2211
--- /dev/null
+++ b/rust/macros/fmt.rs
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro::{Ident, TokenStream, TokenTree};
+use std::collections::BTreeSet;
+
+/// Please see [`crate::fmt`] for documentation.
+pub(crate) fn fmt(input: TokenStream) -> TokenStream {
+    let mut input = input.into_iter();
+
+    let first_opt = input.next();
+    let first_owned_str;
+    let mut names = BTreeSet::new();
+    let first_span = {
+        let Some((mut first_str, first_span)) = (match first_opt.as_ref() {
+            Some(TokenTree::Literal(first_lit)) => {
+                first_owned_str = first_lit.to_string();
+                Some(first_owned_str.as_str()).and_then(|first| {
+                    let first = first.strip_prefix('"')?;
+                    let first = first.strip_suffix('"')?;
+                    Some((first, first_lit.span()))
+                })
+            }
+            _ => None,
+        }) else {
+            return first_opt.into_iter().chain(input).collect();
+        };
+
+        // Parse `identifier`s from the format string.
+        //
+        // See https://doc.rust-lang.org/std/fmt/index.html#syntax.
+        while let Some((_, rest)) = first_str.split_once('{') {
+            first_str = rest;
+            if let Some(rest) = first_str.strip_prefix('{') {
+                first_str = rest;
+                continue;
+            }
+            if let Some((name, rest)) = first_str.split_once('}') {
+                first_str = rest;
+                let name = name.split_once(':').map_or(name, |(name, _)| name);
+                if !name.is_empty() && !name.chars().all(|c| c.is_ascii_digit()) {
+                    names.insert(name);
+                }
+            }
+        }
+        first_span
+    };
+
+    let adapter = quote_spanned!(first_span => ::kernel::fmt::Adapter);
+
+    let mut args = TokenStream::from_iter(first_opt);
+    {
+        let mut flush = |args: &mut TokenStream, current: &mut TokenStream| {
+            let current = std::mem::take(current);
+            if !current.is_empty() {
+                let (lhs, rhs) = (|| {
+                    let mut current = current.into_iter();
+                    let mut acc = TokenStream::new();
+                    while let Some(tt) = current.next() {
+                        // Split on `=` only once to handle cases like `a = b = c`.
+                        if matches!(&tt, TokenTree::Punct(p) if p.as_char() == '=') {
+                            names.remove(acc.to_string().as_str());
+                            // Include the `=` itself to keep the handling below uniform.
+                            acc.extend([tt]);
+                            return (Some(acc), current.collect::<TokenStream>());
+                        }
+                        acc.extend([tt]);
+                    }
+                    (None, acc)
+                })();
+                args.extend(quote_spanned!(first_span => #lhs #adapter(&#rhs)));
+            }
+        };
+
+        let mut current = TokenStream::new();
+        for tt in input {
+            match &tt {
+                TokenTree::Punct(p) if p.as_char() == ',' => {
+                    flush(&mut args, &mut current);
+                    &mut args
+                }
+                _ => &mut current,
+            }
+            .extend([tt]);
+        }
+        flush(&mut args, &mut current);
+    }
+
+    for name in names {
+        let name = Ident::new(name, first_span);
+        args.extend(quote_spanned!(first_span => , #name = #adapter(&#name)));
+    }
+
+    quote_spanned!(first_span => ::core::format_args!(#args))
+}
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index fa847cf3a9b5..793f712dbf7c 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -15,6 +15,7 @@
 mod quote;
 mod concat_idents;
 mod export;
+mod fmt;
 mod helpers;
 mod kunit;
 mod module;
@@ -201,6 +202,24 @@ pub fn export(attr: TokenStream, ts: TokenStream) -> TokenStream {
     export::export(attr, ts)
 }
 
+/// Like [`core::format_args!`], but automatically wraps arguments in [`kernel::fmt::Adapter`].
+///
+/// This macro allows generating `fmt::Arguments` while ensuring that each argument is wrapped with
+/// `::kernel::fmt::Adapter`, which customizes formatting behavior for kernel logging.
+///
+/// Named arguments used in the format string (e.g. `{foo}`) are detected and resolved from local
+/// bindings. All positional and named arguments are automatically wrapped.
+///
+/// This macro is an implementation detail of other kernel logging macros like [`pr_info!`] and
+/// should not typically be used directly.
+///
+/// [`kernel::fmt::Adapter`]: ../kernel/fmt/struct.Adapter.html
+/// [`pr_info!`]: ../kernel/macro.pr_info.html
+#[proc_macro]
+pub fn fmt(input: TokenStream) -> TokenStream {
+    fmt::fmt(input)
+}
+
 /// Concatenate two identifiers.
 ///
 /// This is useful in macros that need to declare or reference items with names
diff --git a/rust/macros/quote.rs b/rust/macros/quote.rs
index acc140c18653..ddfc21577539 100644
--- a/rust/macros/quote.rs
+++ b/rust/macros/quote.rs
@@ -48,6 +48,7 @@ macro_rules! quote_spanned {
     ($span:expr => $($tt:tt)*) => {{
         let mut tokens = ::proc_macro::TokenStream::new();
         {
+            #[allow(unused_variables)]
             let span = $span;
             quote_spanned!(@proc tokens span $($tt)*);
         }
@@ -146,6 +147,12 @@ macro_rules! quote_spanned {
         )]);
         quote_spanned!(@proc $v $span $($tt)*);
     };
+    (@proc $v:ident $span:ident & $($tt:tt)*) => {
+        $v.extend([::proc_macro::TokenTree::Punct(
+            ::proc_macro::Punct::new('&', ::proc_macro::Spacing::Alone),
+        )]);
+        quote_spanned!(@proc $v $span $($tt)*);
+    };
     (@proc $v:ident $span:ident _ $($tt:tt)*) => {
         $v.extend([::proc_macro::TokenTree::Ident(
             ::proc_macro::Ident::new("_", $span),

-- 
2.50.1

[PATCH v15 4/4] rust: replace `CStr` with `core::ffi::CStr`

[Tamir Duberstein]

`kernel::ffi::CStr` was introduced in commit d126d2380131 ("rust: str:
add `CStr` type") in November 2022 as an upstreaming of earlier work
that was done in May 2021[0]. That earlier work, having predated the
inclusion of `CStr` in `core`, largely duplicated the implementation of
`std::ffi::CStr`.

`std::ffi::CStr` was moved to `core::ffi::CStr` in Rust 1.64 in
September 2022. Hence replace `kernel::str::CStr` with `core::ffi::CStr`
to reduce our custom code footprint, and retain needed custom
functionality through an extension trait.

Add `CStr` to `ffi` and the kernel prelude.

Link: https://github.com/Rust-for-Linux/linux/commit/faa3cbcca03d0dec8f8e43f1d8d5c0860d98a23f [0]
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
 rust/ffi.rs                     |   2 +
 rust/kernel/device.rs           |   1 +
 rust/kernel/error.rs            |   2 +
 rust/kernel/firmware.rs         |   9 +-
 rust/kernel/prelude.rs          |   4 +-
 rust/kernel/seq_file.rs         |   2 +-
 rust/kernel/str.rs              | 395 +++++++++-------------------------------
 rust/kernel/sync/condvar.rs     |   2 +-
 rust/kernel/sync/lock.rs        |   2 +-
 rust/kernel/sync/lock/global.rs |   2 +-
 10 files changed, 109 insertions(+), 312 deletions(-)

diff --git a/rust/ffi.rs b/rust/ffi.rs
index d60aad792af4..f961e9728f59 100644
--- a/rust/ffi.rs
+++ b/rust/ffi.rs
@@ -46,3 +46,5 @@ macro_rules! alias {
 }
 
 pub use core::ffi::c_void;
+
+pub use core::ffi::CStr;
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 65306e77d97d..449776474044 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -12,6 +12,7 @@
 
 #[cfg(CONFIG_PRINTK)]
 use crate::c_str;
+use crate::str::CStrExt as _;
 
 pub mod property;
 
diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index a41de293dcd1..266947c59322 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -165,6 +165,8 @@ pub fn name(&self) -> Option<&'static CStr> {
         if ptr.is_null() {
             None
         } else {
+            use crate::str::CStrExt as _;
+
             // SAFETY: The string returned by `errname` is static and `NUL`-terminated.
             Some(unsafe { CStr::from_char_ptr(ptr) })
         }
diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index 94e6bb88b903..376e7e77453f 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -4,7 +4,14 @@
 //!
 //! C header: [`include/linux/firmware.h`](srctree/include/linux/firmware.h)
 
-use crate::{bindings, device::Device, error::Error, error::Result, ffi, str::CStr};
+use crate::{
+    bindings,
+    device::Device,
+    error::Error,
+    error::Result,
+    ffi,
+    str::{CStr, CStrExt as _},
+};
 use core::ptr::NonNull;
 
 /// # Invariants
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index f009f198f593..3f286f90cd07 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -16,7 +16,7 @@
 
 pub use ::ffi::{
     c_char, c_int, c_long, c_longlong, c_schar, c_short, c_uchar, c_uint, c_ulong, c_ulonglong,
-    c_ushort, c_void,
+    c_ushort, c_void, CStr,
 };
 
 pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec, Vec};
@@ -40,7 +40,7 @@
 
 pub use super::error::{code::*, Error, Result};
 
-pub use super::{str::CStr, ThisModule};
+pub use super::{str::CStrExt as _, ThisModule};
 
 pub use super::init::InPlaceInit;
 
diff --git a/rust/kernel/seq_file.rs b/rust/kernel/seq_file.rs
index 59fbfc2473f8..855e533813a6 100644
--- a/rust/kernel/seq_file.rs
+++ b/rust/kernel/seq_file.rs
@@ -4,7 +4,7 @@
 //!
 //! C header: [`include/linux/seq_file.h`](srctree/include/linux/seq_file.h)
 
-use crate::{bindings, c_str, fmt, types::NotThreadSafe, types::Opaque};
+use crate::{bindings, c_str, fmt, str::CStrExt as _, types::NotThreadSafe, types::Opaque};
 
 /// A utility for generating the contents of a seq file.
 #[repr(transparent)]
diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 6c892550c0ba..624386cb07be 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -4,10 +4,12 @@
 
 use crate::alloc::{flags::*, AllocError, KVec};
 use crate::fmt::{self, Write};
-use core::ops::{self, Deref, DerefMut, Index};
+use core::ops::{Deref, DerefMut, Index};
 
 use crate::prelude::*;
 
+pub use crate::prelude::CStr;
+
 /// Byte string without UTF-8 validity guarantee.
 #[repr(transparent)]
 pub struct BStr([u8]);
@@ -181,58 +183,17 @@ macro_rules! b_str {
 // - error[E0379]: functions in trait impls cannot be declared const
 #[inline]
 pub const fn as_char_ptr_in_const_context(c_str: &CStr) -> *const c_char {
-    c_str.0.as_ptr()
+    c_str.as_ptr().cast()
 }
 
-/// Possible errors when using conversion functions in [`CStr`].
-#[derive(Debug, Clone, Copy)]
-pub enum CStrConvertError {
-    /// Supplied bytes contain an interior `NUL`.
-    InteriorNul,
-
-    /// Supplied bytes are not terminated by `NUL`.
-    NotNulTerminated,
-}
+mod private {
+    pub trait Sealed {}
 
-impl From<CStrConvertError> for Error {
-    #[inline]
-    fn from(_: CStrConvertError) -> Error {
-        EINVAL
-    }
+    impl Sealed for super::CStr {}
 }
 
-/// A string that is guaranteed to have exactly one `NUL` byte, which is at the
-/// end.
-///
-/// Used for interoperability with kernel APIs that take C strings.
-#[repr(transparent)]
-pub struct CStr([u8]);
-
-impl CStr {
-    /// Returns the length of this string excluding `NUL`.
-    #[inline]
-    pub const fn len(&self) -> usize {
-        self.len_with_nul() - 1
-    }
-
-    /// Returns the length of this string with `NUL`.
-    #[inline]
-    pub const fn len_with_nul(&self) -> usize {
-        if self.0.is_empty() {
-            // SAFETY: This is one of the invariant of `CStr`.
-            // We add a `unreachable_unchecked` here to hint the optimizer that
-            // the value returned from this function is non-zero.
-            unsafe { core::hint::unreachable_unchecked() };
-        }
-        self.0.len()
-    }
-
-    /// Returns `true` if the string only includes `NUL`.
-    #[inline]
-    pub const fn is_empty(&self) -> bool {
-        self.len() == 0
-    }
-
+/// Extensions to [`CStr`].
+pub trait CStrExt: private::Sealed {
     /// Wraps a raw C string pointer.
     ///
     /// # Safety
@@ -240,54 +201,9 @@ pub const fn is_empty(&self) -> bool {
     /// `ptr` must be a valid pointer to a `NUL`-terminated C string, and it must
     /// last at least `'a`. When `CStr` is alive, the memory pointed by `ptr`
     /// must not be mutated.
-    #[inline]
-    pub unsafe fn from_char_ptr<'a>(ptr: *const c_char) -> &'a Self {
-        // SAFETY: The safety precondition guarantees `ptr` is a valid pointer
-        // to a `NUL`-terminated C string.
-        let len = unsafe { bindings::strlen(ptr) } + 1;
-        // SAFETY: Lifetime guaranteed by the safety precondition.
-        let bytes = unsafe { core::slice::from_raw_parts(ptr.cast(), len) };
-        // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
-        // As we have added 1 to `len`, the last byte is known to be `NUL`.
-        unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
-    }
-
-    /// Creates a [`CStr`] from a `[u8]`.
-    ///
-    /// The provided slice must be `NUL`-terminated, does not contain any
-    /// interior `NUL` bytes.
-    pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError> {
-        if bytes.is_empty() {
-            return Err(CStrConvertError::NotNulTerminated);
-        }
-        if bytes[bytes.len() - 1] != 0 {
-            return Err(CStrConvertError::NotNulTerminated);
-        }
-        let mut i = 0;
-        // `i + 1 < bytes.len()` allows LLVM to optimize away bounds checking,
-        // while it couldn't optimize away bounds checks for `i < bytes.len() - 1`.
-        while i + 1 < bytes.len() {
-            if bytes[i] == 0 {
-                return Err(CStrConvertError::InteriorNul);
-            }
-            i += 1;
-        }
-        // SAFETY: We just checked that all properties hold.
-        Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
-    }
-
-    /// Creates a [`CStr`] from a `[u8]` without performing any additional
-    /// checks.
-    ///
-    /// # Safety
-    ///
-    /// `bytes` *must* end with a `NUL` byte, and should only have a single
-    /// `NUL` byte (or the string will be truncated).
-    #[inline]
-    pub const unsafe fn from_bytes_with_nul_unchecked(bytes: &[u8]) -> &CStr {
-        // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
-        unsafe { core::mem::transmute(bytes) }
-    }
+    // This function exists to paper over the fact that `CStr::from_ptr` takes a `*const
+    // core::ffi::c_char` rather than a `*const crate::ffi::c_char`.
+    unsafe fn from_char_ptr<'a>(ptr: *const c_char) -> &'a Self;
 
     /// Creates a mutable [`CStr`] from a `[u8]` without performing any
     /// additional checks.
@@ -296,99 +212,16 @@ pub const fn from_bytes_with_nul(bytes: &[u8]) -> Result<&Self, CStrConvertError
     ///
     /// `bytes` *must* end with a `NUL` byte, and should only have a single
     /// `NUL` byte (or the string will be truncated).
-    #[inline]
-    pub unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut CStr {
-        // SAFETY: Properties of `bytes` guaranteed by the safety precondition.
-        unsafe { &mut *(core::ptr::from_mut(bytes) as *mut CStr) }
-    }
+    unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut Self;
 
     /// Returns a C pointer to the string.
-    ///
-    /// Using this function in a const context is deprecated in favor of
-    /// [`as_char_ptr_in_const_context`] in preparation for replacing `CStr` with `core::ffi::CStr`
-    /// which does not have this method.
-    #[inline]
-    pub const fn as_char_ptr(&self) -> *const c_char {
-        as_char_ptr_in_const_context(self)
-    }
-
-    /// Convert the string to a byte slice without the trailing `NUL` byte.
-    #[inline]
-    pub fn to_bytes(&self) -> &[u8] {
-        &self.0[..self.len()]
-    }
-
-    /// Convert the string to a byte slice without the trailing `NUL` byte.
-    ///
-    /// This function is deprecated in favor of [`Self::to_bytes`] in preparation for replacing
-    /// `CStr` with `core::ffi::CStr` which does not have this method.
-    #[inline]
-    pub fn as_bytes(&self) -> &[u8] {
-        self.to_bytes()
-    }
-
-    /// Convert the string to a byte slice containing the trailing `NUL` byte.
-    #[inline]
-    pub const fn to_bytes_with_nul(&self) -> &[u8] {
-        &self.0
-    }
-
-    /// Convert the string to a byte slice containing the trailing `NUL` byte.
-    ///
-    /// This function is deprecated in favor of [`Self::to_bytes_with_nul`] in preparation for
-    /// replacing `CStr` with `core::ffi::CStr` which does not have this method.
-    #[inline]
-    pub const fn as_bytes_with_nul(&self) -> &[u8] {
-        self.to_bytes_with_nul()
-    }
-
-    /// Yields a [`&str`] slice if the [`CStr`] contains valid UTF-8.
-    ///
-    /// If the contents of the [`CStr`] are valid UTF-8 data, this
-    /// function will return the corresponding [`&str`] slice. Otherwise,
-    /// it will return an error with details of where UTF-8 validation failed.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// # use kernel::str::CStr;
-    /// let cstr = CStr::from_bytes_with_nul(b"foo\0")?;
-    /// assert_eq!(cstr.to_str(), Ok("foo"));
-    /// # Ok::<(), kernel::error::Error>(())
-    /// ```
-    #[inline]
-    pub fn to_str(&self) -> Result<&str, core::str::Utf8Error> {
-        core::str::from_utf8(self.as_bytes())
-    }
-
-    /// Unsafely convert this [`CStr`] into a [`&str`], without checking for
-    /// valid UTF-8.
-    ///
-    /// # Safety
-    ///
-    /// The contents must be valid UTF-8.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// # use kernel::c_str;
-    /// # use kernel::str::CStr;
-    /// let bar = c_str!("ツ");
-    /// // SAFETY: String literals are guaranteed to be valid UTF-8
-    /// // by the Rust compiler.
-    /// assert_eq!(unsafe { bar.as_str_unchecked() }, "ツ");
-    /// ```
-    #[inline]
-    pub unsafe fn as_str_unchecked(&self) -> &str {
-        // SAFETY: TODO.
-        unsafe { core::str::from_utf8_unchecked(self.as_bytes()) }
-    }
+    // This function exists to paper over the fact that `CStr::as_ptr` returns a `*const
+    // core::ffi::c_char` rather than a `*const crate::ffi::c_char`.
+    fn as_char_ptr(&self) -> *const c_char;
 
     /// Convert this [`CStr`] into a [`CString`] by allocating memory and
     /// copying over the string data.
-    pub fn to_cstring(&self) -> Result<CString, AllocError> {
-        CString::try_from(self)
-    }
+    fn to_cstring(&self) -> Result<CString, AllocError>;
 
     /// Converts this [`CStr`] to its ASCII lower case equivalent in-place.
     ///
@@ -399,11 +232,7 @@ pub fn to_cstring(&self) -> Result<CString, AllocError> {
     /// [`to_ascii_lowercase()`].
     ///
     /// [`to_ascii_lowercase()`]: #method.to_ascii_lowercase
-    pub fn make_ascii_lowercase(&mut self) {
-        // INVARIANT: This doesn't introduce or remove NUL bytes in the C
-        // string.
-        self.0.make_ascii_lowercase();
-    }
+    fn make_ascii_lowercase(&mut self);
 
     /// Converts this [`CStr`] to its ASCII upper case equivalent in-place.
     ///
@@ -414,11 +243,7 @@ pub fn make_ascii_lowercase(&mut self) {
     /// [`to_ascii_uppercase()`].
     ///
     /// [`to_ascii_uppercase()`]: #method.to_ascii_uppercase
-    pub fn make_ascii_uppercase(&mut self) {
-        // INVARIANT: This doesn't introduce or remove NUL bytes in the C
-        // string.
-        self.0.make_ascii_uppercase();
-    }
+    fn make_ascii_uppercase(&mut self);
 
     /// Returns a copy of this [`CString`] where each character is mapped to its
     /// ASCII lower case equivalent.
@@ -429,13 +254,7 @@ pub fn make_ascii_uppercase(&mut self) {
     /// To lowercase the value in-place, use [`make_ascii_lowercase`].
     ///
     /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
-    pub fn to_ascii_lowercase(&self) -> Result<CString, AllocError> {
-        let mut s = self.to_cstring()?;
-
-        s.make_ascii_lowercase();
-
-        Ok(s)
-    }
+    fn to_ascii_lowercase(&self) -> Result<CString, AllocError>;
 
     /// Returns a copy of this [`CString`] where each character is mapped to its
     /// ASCII upper case equivalent.
@@ -446,13 +265,7 @@ pub fn to_ascii_lowercase(&self) -> Result<CString, AllocError> {
     /// To uppercase the value in-place, use [`make_ascii_uppercase`].
     ///
     /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
-    pub fn to_ascii_uppercase(&self) -> Result<CString, AllocError> {
-        let mut s = self.to_cstring()?;
-
-        s.make_ascii_uppercase();
-
-        Ok(s)
-    }
+    fn to_ascii_uppercase(&self) -> Result<CString, AllocError>;
 }
 
 impl fmt::Display for CStr {
@@ -485,98 +298,75 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     }
 }
 
-impl fmt::Debug for CStr {
-    /// Formats printable ASCII characters with a double quote on either end, escaping the rest.
-    ///
-    /// ```
-    /// # use kernel::c_str;
-    /// # use kernel::prelude::fmt;
-    /// # use kernel::str::CStr;
-    /// # use kernel::str::CString;
-    /// let penguin = c_str!("🐧");
-    /// let s = CString::try_from_fmt(fmt!("{penguin:?}"))?;
-    /// assert_eq!(s.as_bytes_with_nul(), "\"\\xf0\\x9f\\x90\\xa7\"\0".as_bytes());
-    ///
-    /// // Embedded double quotes are escaped.
-    /// let ascii = c_str!("so \"cool\"");
-    /// let s = CString::try_from_fmt(fmt!("{ascii:?}"))?;
-    /// assert_eq!(s.as_bytes_with_nul(), "\"so \\\"cool\\\"\"\0".as_bytes());
-    /// # Ok::<(), kernel::error::Error>(())
-    /// ```
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str("\"")?;
-        for &c in self.as_bytes() {
-            match c {
-                // Printable characters.
-                b'\"' => f.write_str("\\\"")?,
-                0x20..=0x7e => f.write_char(c as char)?,
-                _ => write!(f, "\\x{c:02x}")?,
-            }
-        }
-        f.write_str("\"")
-    }
+/// Converts a mutable C string to a mutable byte slice.
+///
+/// # Safety
+///
+/// The caller must ensure that the slice ends in a NUL byte and contains no other NUL bytes before
+/// the borrow ends and the underlying [`CStr`] is used.
+unsafe fn to_bytes_mut(s: &mut CStr) -> &mut [u8] {
+    // SAFETY: the cast from `&CStr` to `&[u8]` is safe since `CStr` has the same layout as `&[u8]`
+    // (this is technically not guaranteed, but we rely on it here). The pointer dereference is
+    // safe since it comes from a mutable reference which is guaranteed to be valid for writes.
+    unsafe { &mut *(core::ptr::from_mut(s) as *mut [u8]) }
 }
 
-impl AsRef<BStr> for CStr {
+impl CStrExt for CStr {
     #[inline]
-    fn as_ref(&self) -> &BStr {
-        BStr::from_bytes(self.as_bytes())
+    unsafe fn from_char_ptr<'a>(ptr: *const c_char) -> &'a Self {
+        // SAFETY: The safety preconditions are the same as for `CStr::from_ptr`.
+        unsafe { CStr::from_ptr(ptr.cast()) }
     }
-}
 
-impl Deref for CStr {
-    type Target = BStr;
+    #[inline]
+    unsafe fn from_bytes_with_nul_unchecked_mut(bytes: &mut [u8]) -> &mut Self {
+        // SAFETY: the cast from `&[u8]` to `&CStr` is safe since the properties of `bytes` are
+        // guaranteed by the safety precondition and `CStr` has the same layout as `&[u8]` (this is
+        // technically not guaranteed, but we rely on it here). The pointer dereference is safe
+        // since it comes from a mutable reference which is guaranteed to be valid for writes.
+        unsafe { &mut *(core::ptr::from_mut(bytes) as *mut CStr) }
+    }
 
     #[inline]
-    fn deref(&self) -> &Self::Target {
-        self.as_ref()
+    fn as_char_ptr(&self) -> *const c_char {
+        self.as_ptr().cast()
+    }
+
+    fn to_cstring(&self) -> Result<CString, AllocError> {
+        CString::try_from(self)
     }
-}
 
-impl Index<ops::RangeFrom<usize>> for CStr {
-    type Output = CStr;
+    fn make_ascii_lowercase(&mut self) {
+        // SAFETY: This doesn't introduce or remove NUL bytes in the C string.
+        unsafe { to_bytes_mut(self) }.make_ascii_lowercase();
+    }
 
-    #[inline]
-    fn index(&self, index: ops::RangeFrom<usize>) -> &Self::Output {
-        // Delegate bounds checking to slice.
-        // Assign to _ to mute clippy's unnecessary operation warning.
-        let _ = &self.as_bytes()[index.start..];
-        // SAFETY: We just checked the bounds.
-        unsafe { Self::from_bytes_with_nul_unchecked(&self.0[index.start..]) }
+    fn make_ascii_uppercase(&mut self) {
+        // SAFETY: This doesn't introduce or remove NUL bytes in the C string.
+        unsafe { to_bytes_mut(self) }.make_ascii_uppercase();
     }
-}
 
-impl Index<ops::RangeFull> for CStr {
-    type Output = CStr;
+    fn to_ascii_lowercase(&self) -> Result<CString, AllocError> {
+        let mut s = self.to_cstring()?;
 
-    #[inline]
-    fn index(&self, _index: ops::RangeFull) -> &Self::Output {
-        self
+        s.make_ascii_lowercase();
+
+        Ok(s)
     }
-}
 
-mod private {
-    use core::ops;
+    fn to_ascii_uppercase(&self) -> Result<CString, AllocError> {
+        let mut s = self.to_cstring()?;
 
-    // Marker trait for index types that can be forward to `BStr`.
-    pub trait CStrIndex {}
+        s.make_ascii_uppercase();
 
-    impl CStrIndex for usize {}
-    impl CStrIndex for ops::Range<usize> {}
-    impl CStrIndex for ops::RangeInclusive<usize> {}
-    impl CStrIndex for ops::RangeToInclusive<usize> {}
+        Ok(s)
+    }
 }
 
-impl<Idx> Index<Idx> for CStr
-where
-    Idx: private::CStrIndex,
-    BStr: Index<Idx>,
-{
-    type Output = <BStr as Index<Idx>>::Output;
-
+impl AsRef<BStr> for CStr {
     #[inline]
-    fn index(&self, index: Idx) -> &Self::Output {
-        &self.as_ref()[index]
+    fn as_ref(&self) -> &BStr {
+        BStr::from_bytes(self.to_bytes())
     }
 }
 
@@ -607,6 +397,13 @@ macro_rules! c_str {
 mod tests {
     use super::*;
 
+    impl From<core::ffi::FromBytesWithNulError> for Error {
+        #[inline]
+        fn from(_: core::ffi::FromBytesWithNulError) -> Error {
+            EINVAL
+        }
+    }
+
     macro_rules! format {
         ($($f:tt)*) => ({
             CString::try_from_fmt(fmt!($($f)*))?.to_str()?
@@ -629,40 +426,28 @@ macro_rules! format {
 
     #[test]
     fn test_cstr_to_str() -> Result {
-        let good_bytes = b"\xf0\x9f\xa6\x80\0";
-        let checked_cstr = CStr::from_bytes_with_nul(good_bytes)?;
-        let checked_str = checked_cstr.to_str()?;
+        let cstr = c"\xf0\x9f\xa6\x80";
+        let checked_str = cstr.to_str()?;
         assert_eq!(checked_str, "🦀");
         Ok(())
     }
 
     #[test]
     fn test_cstr_to_str_invalid_utf8() -> Result {
-        let bad_bytes = b"\xc3\x28\0";
-        let checked_cstr = CStr::from_bytes_with_nul(bad_bytes)?;
-        assert!(checked_cstr.to_str().is_err());
-        Ok(())
-    }
-
-    #[test]
-    fn test_cstr_as_str_unchecked() -> Result {
-        let good_bytes = b"\xf0\x9f\x90\xA7\0";
-        let checked_cstr = CStr::from_bytes_with_nul(good_bytes)?;
-        // SAFETY: The contents come from a string literal which contains valid UTF-8.
-        let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
-        assert_eq!(unchecked_str, "🐧");
+        let cstr = c"\xc3\x28";
+        assert!(cstr.to_str().is_err());
         Ok(())
     }
 
     #[test]
     fn test_cstr_display() -> Result {
-        let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0")?;
+        let hello_world = c"hello, world!";
         assert_eq!(format!("{hello_world}"), "hello, world!");
-        let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0")?;
+        let non_printables = c"\x01\x09\x0a";
         assert_eq!(format!("{non_printables}"), "\\x01\\x09\\x0a");
-        let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0")?;
+        let non_ascii = c"d\xe9j\xe0 vu";
         assert_eq!(format!("{non_ascii}"), "d\\xe9j\\xe0 vu");
-        let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0")?;
+        let good_bytes = c"\xf0\x9f\xa6\x80";
         assert_eq!(format!("{good_bytes}"), "\\xf0\\x9f\\xa6\\x80");
         Ok(())
     }
@@ -681,13 +466,13 @@ fn test_cstr_display_all_bytes() -> Result {
 
     #[test]
     fn test_cstr_debug() -> Result {
-        let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0")?;
+        let hello_world = c"hello, world!";
         assert_eq!(format!("{hello_world:?}"), "\"hello, world!\"");
-        let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0")?;
-        assert_eq!(format!("{non_printables:?}"), "\"\\x01\\x09\\x0a\"");
-        let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0")?;
+        let non_printables = c"\x01\x09\x0a";
+        assert_eq!(format!("{non_printables:?}"), "\"\\x01\\t\\n\"");
+        let non_ascii = c"d\xe9j\xe0 vu";
         assert_eq!(format!("{non_ascii:?}"), "\"d\\xe9j\\xe0 vu\"");
-        let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0")?;
+        let good_bytes = c"\xf0\x9f\xa6\x80";
         assert_eq!(format!("{good_bytes:?}"), "\"\\xf0\\x9f\\xa6\\x80\"");
         Ok(())
     }
diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index c6ec64295c9f..a24e25a690ee 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -8,7 +8,7 @@
 use super::{lock::Backend, lock::Guard, LockClassKey};
 use crate::{
     ffi::{c_int, c_long},
-    str::CStr,
+    str::{CStr, CStrExt as _},
     task::{
         MAX_SCHEDULE_TIMEOUT, TASK_FREEZABLE, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE,
     },
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 27202beef90c..5d7991e6d373 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -7,7 +7,7 @@
 
 use super::LockClassKey;
 use crate::{
-    str::CStr,
+    str::{CStr, CStrExt as _},
     types::{NotThreadSafe, Opaque, ScopeGuard},
 };
 use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index d65f94b5caf2..79d0ef7fda86 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -5,7 +5,7 @@
 //! Support for defining statics containing locks.
 
 use crate::{
-    str::CStr,
+    str::{CStr, CStrExt as _},
     sync::lock::{Backend, Guard, Lock},
     sync::{LockClassKey, LockedBy},
     types::Opaque,

-- 
2.50.1