linux-kernel - Re: [PATCH v6 06/18] rust: str: add `bytes_to

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Message-Id: <60D09FDF-D1EB-46A0-8F76-13F98BE9C518@collabora.com>
Date: Wed, 27 Aug 2025 10:46:18 -0300
From: Daniel Almeida <daniel.almeida@...labora.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>,
 Alice Ryhl <aliceryhl@...gle.com>,
 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 v6 06/18] rust: str: add `bytes_to_bool` helper function



> On 22 Aug 2025, at 09:14, Andreas Hindborg <a.hindborg@...nel.org> wrote:
> 
> Add a convenience function to convert byte slices to boolean values by
> wrapping them in a null-terminated C string and delegating to the
> existing `kstrtobool` function. Only considers the first two bytes of
> the input slice, following the kernel's boolean parsing semantics.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
> rust/kernel/str.rs | 35 +++++++++++++++++++++++++++++------
> 1 file changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index d070c0bd86c3..b185262b4851 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -921,6 +921,20 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
>     }
> }
> 
> +/// # Safety
> +///
> +/// - `string` must point to a null terminated string that is valid for read.
> +unsafe fn kstrtobool_raw(string: *const u8) -> Result<bool> {
> +    let mut result: bool = false;
> +
> +    // SAFETY:
> +    // - By function safety requirement, `string` is a valid null-terminated string.
> +    // - `result` is a valid `bool` that we own.
> +    let ret = unsafe { bindings::kstrtobool(string, &mut result) };
> +
> +    kernel::error::to_result(ret).map(|()| 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
> @@ -968,13 +982,22 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
> /// 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(), &mut result) };
> +    // SAFETY:
> +    // - The pointer returned by `CStr::as_char_ptr` is guaranteed to be
> +    //   null terminated.
> +    // - `string` is live and thus the string is valid for read.
> +    unsafe { kstrtobool_raw(string.as_char_ptr()) }
> +}
> 
> -    kernel::error::to_result(ret).map(|()| result)
> +/// Convert `&[u8]` to `bool` by deferring to [`kernel::str::kstrtobool`].
> +///
> +/// Only considers at most the first two bytes of `bytes`.
> +pub fn kstrtobool_bytes(bytes: &[u8]) -> Result<bool> {
> +    // `ktostrbool` only considers the first two bytes of the input.
> +    let stack_string = [*bytes.first().unwrap_or(&0), *bytes.get(1).unwrap_or(&0), 0];

Can’t this be CStr::from_bytes_with_nul() ?

This means that kstrtobool_raw could take a &CStr directly and thus not be unsafe IIUC?

> +    // SAFETY: `stack_string` is null terminated and it is live on the stack so
> +    // it is valid for read.
> +    unsafe { kstrtobool_raw(stack_string.as_ptr()) }
> }
> 
> /// An owned string that is guaranteed to have exactly one `NUL` byte, which is at the end.
> 
> -- 
> 2.47.2
> 
> 
>