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

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Message-ID: <87zfc2e4gy.fsf@t14s.mail-host-address-is-not-set>
Date: Thu, 14 Aug 2025 09:40:13 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
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`

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> 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.

If we re-implement the entire function in rust, we can do the processing
on a `&str`. That way, we can skip the allocation to enforce null
termination. At least for this use case. I would rather do a utf8 check
than allocate and copy.


Best regards,
Andreas Hindborg