linux-kernel - Re: [PATCH v11 4/5] rust: replace `kernel::c

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Message-ID: <aD1knOuEFxv6VQy1@google.com>
Date: Mon, 2 Jun 2025 08:45:16 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Michal Rostecki <vadorovsky@...tonmail.com>, Miguel Ojeda <ojeda@...nel.org>, 
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Subject: Re: [PATCH v11 4/5] rust: replace `kernel::c_str!` with C-Strings

On Fri, May 30, 2025 at 08:27:45AM -0400, Tamir Duberstein wrote:
> C-String literals were added in Rust 1.77. Replace instances of
> `kernel::c_str!` with C-String literals where possible and rename
> `kernel::c_str!` to `str_to_cstr!` to clarify its intended use.
> 
> Closes: https://github.com/Rust-for-Linux/linux/issues/1075
> Signed-off-by: Tamir Duberstein <tamird@...il.com>

> -/// Creates a new [`CStr`] from a string literal.
> +/// Creates a static C string wrapper at compile time.

A C string *wrapper*? What do you mean? I would drop the word "wrapper"
here.

> -/// The string literal should not contain any `NUL` bytes.
> +/// Rust supports C string literals since Rust 1.77, and they should be used instead of this macro
> +/// where possible. This macro exists to allow static *non-literal* C strings to be created at
> +/// compile time. This is most often used in other macros.
> +///
> +/// # Panics
> +///
> +/// This macro panics if the operand contains an interior `NUL` byte.
>  ///
>  /// # Examples
>  ///
>  /// ```
> -/// # use kernel::c_str;
> +/// # use kernel::str_to_cstr;
>  /// # use kernel::str::CStr;
> -/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
> +/// const MY_CSTR: &CStr = str_to_cstr!(concat!(file!(), ":", line!(), ": My CStr!"));
>  /// ```
>  #[macro_export]
> -macro_rules! c_str {
> +macro_rules! str_to_cstr {
> +    // NB: we could write `($str:lit) => compile_error!("use a C string literal instead");` here but
> +    // that would trigger when the literal is at the top of several macro expansions. That would be
> +    // too limiting to macro authors, so we rely on the name as a hint instead.
>      ($str:expr) => {{
>          const S: &str = concat!($str, "\0");
>          const C: &$crate::str::CStr = match $crate::str::CStr::from_bytes_with_nul(S.as_bytes()) {

Alice