Re: [PATCH v4 1/2] rust: add `Alignment` type

["Alexandre Courbot" <acourbot@nvidia.com>]

On Mon Sep 8, 2025 at 9:02 PM JST, Danilo Krummrich wrote:
> On 8/21/25 2:42 PM, Alexandre Courbot wrote:
>> +    /// Validates that `align` is a power of two at build-time, and returns an [`Alignment`] of the
>> +    /// same value.
>> +    ///
>> +    /// A build error is triggered if `align` cannot be asserted to be a power of two.
>> +    ///
>> +    /// # Examples
>> +    ///
>> +    /// ```
>> +    /// use kernel::ptr::Alignment;
>> +    ///
>> +    /// let v = Alignment::new(16);
>> +    /// assert_eq!(v.as_usize(), 16);
>> +    /// ```
>> +    #[inline(always)]
>> +    pub const fn new(align: usize) -> Self {
>> +        build_assert!(align.is_power_of_two());
>> +
>> +        // INVARIANT: `align` is a power of two.
>> +        // SAFETY: `align` is a power of two, and thus non-zero.
>> +        Self(unsafe { NonZero::new_unchecked(align) })
>> +    }
>
> For DmaMask::new() we used a const generic instead, which makes it more obvious
> to the caller that the argument must be known at compile time. So, I'd prefer
> this here as well.

Ah, being consistent is good, and I think I prefer the const generic as
well. Let's do the same thing here.