linux-kernel - Re: [PATCH v4 11/15] rnull: enable configuration via `configfs`

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Message-ID: <CAH5fLgi+R=ZW2bFnZP2=231vV6JAHTZJ0UBYkdojG=HjBYR3MA@mail.gmail.com>
Date: Wed, 13 Aug 2025 20:05:02 +0200
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>, linux-block@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 11/15] rnull: enable configuration via `configfs`

On Wed, Aug 13, 2025 at 7:36 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> "Alice Ryhl" <aliceryhl@...gle.com> writes:
>
> > For your convenience, I already wrote a safe wrapper of kstrtobool for
> > an out-of-tree driver. You're welcome to copy-paste this:
> >
> > fn kstrtobool(kstr: &CStr) -> Result<bool> {
> >     let mut res = false;
> >     to_result(unsafe {
> > kernel::bindings::kstrtobool(kstr.as_char_ptr(), &mut res) })?;
> >     Ok(res)
> > }
>
> Thanks, I did one as well today, accepting `&str` instead. The examples
> highlight why it is not great:

Yeah, well, I think we should still use it for consistency.

>   /// 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::str::kstrtobool;
>   ///
>   /// // Lowercase
>   /// assert_eq!(kstrtobool("true"), Ok(true));
>   /// assert_eq!(kstrtobool("tr"), Ok(true));
>   /// assert_eq!(kstrtobool("t"), Ok(true));
>   /// assert_eq!(kstrtobool("twrong"), Ok(true)); // <-- 🤷
>   /// assert_eq!(kstrtobool("false"), Ok(false));
>   /// assert_eq!(kstrtobool("f"), Ok(false));
>   /// assert_eq!(kstrtobool("yes"), Ok(true));
>   /// assert_eq!(kstrtobool("no"), Ok(false));
>   /// assert_eq!(kstrtobool("on"), Ok(true));
>   /// assert_eq!(kstrtobool("off"), Ok(false));
>   ///
>   /// // Camel case
>   /// assert_eq!(kstrtobool("True"), Ok(true));
>   /// assert_eq!(kstrtobool("False"), Ok(false));
>   /// assert_eq!(kstrtobool("Yes"), Ok(true));
>   /// assert_eq!(kstrtobool("No"), Ok(false));
>   /// assert_eq!(kstrtobool("On"), Ok(true));
>   /// assert_eq!(kstrtobool("Off"), Ok(false));
>   ///
>   /// // All caps
>   /// assert_eq!(kstrtobool("TRUE"), Ok(true));
>   /// assert_eq!(kstrtobool("FALSE"), Ok(false));
>   /// assert_eq!(kstrtobool("YES"), Ok(true));
>   /// assert_eq!(kstrtobool("NO"), Ok(false));
>   /// assert_eq!(kstrtobool("ON"), Ok(true));
>   /// assert_eq!(kstrtobool("OFF"), Ok(false));
>   ///
>   /// // Numeric
>   /// assert_eq!(kstrtobool("1"), Ok(true));
>   /// assert_eq!(kstrtobool("0"), Ok(false));
>   ///
>   /// // Invalid input
>   /// assert_eq!(kstrtobool("invalid"), Err(EINVAL));
>   /// assert_eq!(kstrtobool("2"), Err(EINVAL));
>   /// ```
>   pub fn kstrtobool(input: &str) -> Result<bool> {
>       let mut result: bool = false;
>       let c_str = CString::try_from_fmt(fmt!("{input}"))?;
>
>       // SAFETY: `c_str` points to a valid null-terminated C string, and `result` is a valid
>       // pointer to a bool that we own.
>       let ret = unsafe { bindings::kstrtobool(c_str.as_char_ptr(), &mut result as *mut bool) };
>
>       kernel::error::to_result(ret).map(|_| result)
>   }
>
> Not sure if we should take `CStr` or `str`, what do you think?

Using CStr makes sense, since it avoids having the caller perform a
useless utf-8 check.

Alice