linux-kernel - Re: [PATCH v5 05/18] rust: str: introduce `kstrtobool` function

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Message-ID: <aJ7oY9pxlrnfAv8s@google.com>
Date: Fri, 15 Aug 2025 07:57:23 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Jens Axboe <axboe@...nel.dk>, 
	Breno Leitao <leitao@...ian.org>, linux-block@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 05/18] rust: str: introduce `kstrtobool` function

On Fri, Aug 15, 2025 at 09:30:40AM +0200, Andreas Hindborg wrote:
> Add a Rust wrapper for the kernel's `kstrtobool` function that converts
> common user inputs into boolean values.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/kernel/str.rs | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index d8326f7bc9c1..5611f7846dc0 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -4,6 +4,7 @@
>  
>  use crate::{
>      alloc::{flags::*, AllocError, KVec},
> +    error::Result,
>      fmt::{self, Write},
>      prelude::*,
>  };
> @@ -920,6 +921,63 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
>      }
>  }
>  
> +/// Convert common user inputs into boolean values using the kernel's `kstrtobool` function.
> +///
> +/// This routine returns `Ok(bool)` if the first character is one of 'YyTt1NnFf0', or
> +/// \[oO\]\[NnFf\] for "on" and "off". Otherwise it will return `Err(EINVAL)`.
> +///
> +/// # Examples
> +///
> +/// ```
> +/// # use kernel::{c_str, str::kstrtobool};
> +///
> +/// // Lowercase
> +/// assert_eq!(kstrtobool(c_str!("true")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("tr")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("t")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("twrong")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("false")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("f")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("yes")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("no")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("on")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("off")), Ok(false));
> +///
> +/// // Camel case
> +/// assert_eq!(kstrtobool(c_str!("True")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("False")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("Yes")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("No")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("On")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("Off")), Ok(false));
> +///
> +/// // All caps
> +/// assert_eq!(kstrtobool(c_str!("TRUE")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("FALSE")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("YES")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("NO")), Ok(false));
> +/// assert_eq!(kstrtobool(c_str!("ON")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("OFF")), Ok(false));
> +///
> +/// // Numeric
> +/// assert_eq!(kstrtobool(c_str!("1")), Ok(true));
> +/// assert_eq!(kstrtobool(c_str!("0")), Ok(false));
> +///
> +/// // Invalid input
> +/// assert_eq!(kstrtobool(c_str!("invalid")), Err(EINVAL));
> +/// assert_eq!(kstrtobool(c_str!("2")), Err(EINVAL));
> +/// ```
> +pub fn kstrtobool(string: &CStr) -> Result<bool> {
> +    let mut result: bool = false;
> +
> +    // SAFETY: `string` is a valid null-terminated C string, and `result` is a valid
> +    // pointer to a bool that we own.
> +    let ret =
> +        unsafe { bindings::kstrtobool(string.as_char_ptr(), core::ptr::from_mut(&mut result)) };

Using ptr::from_mut here seesm excessive IMO. I think that function
makes sense when it replaces an explicit `as` cast, but now when it can
be done by a coercion. This is perfectly readable:

let ret = unsafe { bindings::kstrtobool(string.as_char_ptr(), &mut result) };

Or if you insist, you could directly create a raw pointer:

let ret = unsafe { bindings::kstrtobool(string.as_char_ptr(), &raw mut result) };

Alice