Re: [PATCH v5] rust: Return Option from page_align and ensure no usize overflow

[Brendan Shephard <bshephar@bne-home.net>]

On Mon, Dec 01, 2025 at 10:15:43AM +0000, Alice Ryhl wrote:
> >  /// Round up the given number to the next multiple of [`PAGE_SIZE`].
> >  ///
> > -/// It is incorrect to pass an address where the next multiple of [`PAGE_SIZE`] doesn't fit in a
> > -/// [`usize`].
> > -pub const fn page_align(addr: usize) -> usize {
> > -    // Parentheses around `PAGE_SIZE - 1` to avoid triggering overflow sanitizers in the wrong
> > -    // cases.
> > -    (addr + (PAGE_SIZE - 1)) & PAGE_MASK
> > +/// Returns a page aligned [`usize`] in cases where the value can be aligned. Otherwise, returns [`None`]
> > +/// if the aligned size will overflow a [`usize`].
> 
> The first line of doc-comments is shown on the module docs. I think it'd
> be nice to shorten the first line.
> 
> /// Rounds up to the next multiple of [`PAGE_SIZE`].
> ///
> /// Returns `None` on integer overflow.
> 
> People reading the module docs will get what they need from "Rounds up
> to the next multiple of PAGE_SIZE.", and if they want to know details
> such as overflow behavior they can read the page specific to this
> method.
> 
> Alice
> 
> 

Seems reasonable, v6 sent with this adjustment:
https://lore.kernel.org/rust-for-linux/aS6y5blasMX0KcD7@fedora/T/#u

Thanks!

Brendan