Re: [PATCH] uaccess: rust: add strncpy_from_user

[Miguel Ojeda]

On Thu, Apr 24, 2025 at 5:18 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
>
> +    if res < 0 {
> +        Err(Error::from_errno(res as i32))
> +    } else {
> +        #[cfg(CONFIG_RUST_OVERFLOW_CHECKS)]
> +        assert!(res <= len);
> +        Ok(res as usize)
> +    }

What about:

    if res < 0 {
        return Err(...);
    }

    overflow_assert!(res <= len);
    Ok(res as usize)

That follows a bit better what is usually done on the C side, in using
early returns (especially for error paths) and in avoiding local
`#ifdef`s.

Of course, we can leave this `overflow_assert!` to a different patch
later on with this code as an example use case, or a good first issue
etc. It also allows to document it etc. Happy to send it or create the
issue.

(I wrote that instead of `assert_overflow!` because it follows the
`{static,debug}_assert!` patterns, i.e. it changes more the "kind" of
assert rather than asserting a particular thing, like `_eq!` or
`_same_type!`).

Thanks!

Cheers,
Miguel