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

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

On Fri, Nov 28, 2025 at 03:12:13AM +0100, Miguel Ojeda wrote:
> On Fri, Nov 28, 2025 at 1:29 AM Alexandre Courbot <acourbot@nvidia.com> wrote:
> >
> > Ah, indeed. In that case, can we make the if arms symmetric:
> >
> >     if let Some(sum) = addr.checked_add(PAGE_SIZE - 1) {
> >         Some(sum & PAGE_MASK);
> >     } else {
> >         None
> >     }
> 
> Early return style makes the happy path less indented and is more
> consistent with the C side. However, here the happy case would be the
> indented case, so `let else` would be better:
> 
>     let Some(sum) = addr.checked_add(PAGE_SIZE - 1) else {
>         return None;
>     };
> 
>     Some(sum & PAGE_MASK)
> 
> Cheers,
> Miguel
> 

A wildcard entrant to this conversation. We could do a match instead if
you all might prefer that?

match addr.checked_add(PAGE_SIZE - 1) {
  Some(v) => Some(v & PAGE_MASK),
  None => None,
}

Something about that match syntax doesn't appeal to me though. I think I
prefer Miguel's suggestion here where we flip the happy and sad paths.
Make the sad path the early return and happy path the default. But I do
see at least a couple of `match` examples here, so it's probably worth a
mention to see what you think about it as an alternative?