linux-kernel - Re: [PATCH v11 3/5] rust: replace `CStr` with `core::ffi::CStr`

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Message-ID: <aD1k4rRK8Pt5Tkva@google.com>
Date: Mon, 2 Jun 2025 08:46:26 +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 3/5] rust: replace `CStr` with `core::ffi::CStr`

On Fri, May 30, 2025 at 08:27:44AM -0400, Tamir Duberstein wrote:
> `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.
> 
> C-String literals were added in Rust 1.77, while our MSRV is 1.78. Thus
> opportunistically replace instances of `kernel::c_str!` with C-String
> literals where other code changes were already necessary or where
> existing code triggered clippy lints; the rest will be done in a later
> commit.
> 
> Link: https://github.com/Rust-for-Linux/linux/commit/faa3cbcca03d0dec8f8e43f1d8d5c0860d98a23f [0]
> Signed-off-by: Tamir Duberstein <tamird@...il.com>

> diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
> index 2494c96e105f..582ab648b14c 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 _},
> +};

Did you not add CStrExt to the prelude?

> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -164,6 +164,8 @@ 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) })
>          }

Ditto here.

Alice