linux-kernel - Re: [PATCH v12 1/3] rust: str: add radix prefixed integer parsing functions

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Message-Id: <D9PSYQMCW74W.39JB3NDCWB2H3@kernel.org>
Date: Wed, 07 May 2025 10:58:08 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Andreas Hindborg" <a.hindborg@...nel.org>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <benno.lossin@...ton.me>, "Alice Ryhl" <aliceryhl@...gle.com>, "Masahiro
 Yamada" <masahiroy@...nel.org>, "Nathan Chancellor" <nathan@...nel.org>,
 "Luis Chamberlain" <mcgrof@...nel.org>, "Danilo Krummrich"
 <dakr@...nel.org>, "Nicolas Schier" <nicolas.schier@...ux.dev>
Cc: "Trevor Gross" <tmgross@...ch.edu>, "Adam Bratschi-Kaye"
 <ark.email@...il.com>, <rust-for-linux@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-kbuild@...r.kernel.org>, "Petr
 Pavlu" <petr.pavlu@...e.com>, "Sami Tolvanen" <samitolvanen@...gle.com>,
 "Daniel Gomez" <da.gomez@...sung.com>, "Simona Vetter"
 <simona.vetter@...ll.ch>, "Greg KH" <gregkh@...uxfoundation.org>, "Fiona
 Behrens" <me@...enk.dev>, "Daniel Almeida" <daniel.almeida@...labora.com>,
 <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v12 1/3] rust: str: add radix prefixed integer parsing
 functions

On Tue May 6, 2025 at 3:02 PM CEST, Andreas Hindborg wrote:
> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> index 878111cb77bc..174e70397305 100644
> --- a/rust/kernel/str.rs
> +++ b/rust/kernel/str.rs
> @@ -573,7 +573,6 @@ macro_rules! c_str {
>  }
>  
>  #[cfg(test)]
> -#[expect(clippy::items_after_test_module)]
>  mod tests {
>      use super::*;
>  
> @@ -946,3 +945,174 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
>  macro_rules! fmt {
>      ($($f:tt)*) => ( core::format_args!($($f)*) )
>  }
> +
> +/// Integer parsing functions for parsing signed and unsigned integers
> +/// potentially prefixed with `0x`, `0o`, or `0b`.
> +pub mod parse_int {

Why not make this its own file? It's 172 lines long already.

> +    pub trait ParseInt: private::FromStrRadix + TryFrom<u64> {
> +        /// Parse a string according to the description in [`Self`].
> +        fn from_str(src: &BStr) -> Result<Self> {
> +            match src.deref() {
> +                [b'-', rest @ ..] => {
> +                    let (radix, digits) = strip_radix(rest.as_ref());
> +                    // 2's complement values range from -2^(b-1) to 2^(b-1)-1.
> +                    // So if we want to parse negative numbers as positive and
> +                    // later multiply by -1, we have to parse into a larger
> +                    // integer. We choose `u64` as sufficiently large.
> +                    //
> +                    // NOTE: 128 bit integers are not available on all
> +                    // platforms, hence the choice of 64 bits.
> +                    let val = u64::from_str_radix(
> +                        core::str::from_utf8(digits).map_err(|_| EINVAL)?,
> +                        radix,
> +                    )
> +                    .map_err(|_| EINVAL)?;
> +
> +                    if val > Self::abs_min() {
> +                        return Err(EINVAL);
> +                    }
> +
> +                    if val == Self::abs_min() {
> +                        return Ok(Self::MIN);
> +                    }
> +
> +                    // SAFETY: We checked that `val` will fit in `Self` above.
> +                    let val: Self = unsafe { val.try_into().unwrap_unchecked() };
> +
> +                    Ok(val.complement())

You're allowing to parse `u32` with a leading `-`? I'd expect an error
in that case. Maybe `complement` should be named `negate` and return a
`Result`?

---
Cheers,
Benno

> +                }
> +                _ => {
> +                    let (radix, digits) = strip_radix(src);
> +                    Self::from_str_radix(digits, radix).map_err(|_| EINVAL)
> +                }
> +            }
> +        }
> +    }