Re: [PATCH v2] rust: page: add Rust version of PAGE_ALIGN

[John Hubbard <jhubbard@nvidia.com>]

On 10/16/24 4:34 AM, Alice Ryhl wrote:
> This is a useful for helper for working with indices into buffers that
> consist of several pages. I forgot to include it when I added PAGE_SIZE
> and PAGE_MASK for the same purpose in commit fc6e66f4696b ("rust: add
> abstraction for `struct page`").
> 
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> Changes in v2:
> - Make the function const.
> - Address integer overflow in docs.
> - Link to v1: https://lore.kernel.org/r/20241015-page-align-v1-1-68fbd8b6d10c@google.com
> ---
>   rust/kernel/page.rs | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 208a006d587c..9ef01929e7d0 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs
> @@ -20,6 +20,15 @@
>   /// A bitmask that gives the page containing a given address.
>   pub const PAGE_MASK: usize = !(PAGE_SIZE - 1);
>   
> +/// 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 {
> +    // Brackets around PAGE_SIZE-1 to avoid triggering overflow sanitizers in the wrong cases.

Silly nit, but I did start looking for brackets that aren't there, so:

s/Brackets/parentheses/


> +    (addr + (PAGE_SIZE - 1)) & PAGE_MASK
> +}
> +
>   /// A pointer to a page that owns the page allocation.
>   ///
>   /// # Invariants
> 
> ---
> base-commit: 8d8f785ceb21b9a0de11e05b811cc52d6fa79318
> change-id: 20241015-page-align-7e5fa4c751be
> 
> Best regards,

thanks,
-- 
John Hubbard