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

[Boqun Feng <boqun.feng@gmail.com>]

On Tue, Oct 15, 2024 at 02:28:28PM +0000, 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`").
> 
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/page.rs | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 208a006d587c..90846e3fe829 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs
> @@ -20,6 +20,11 @@
>  /// A bitmask that gives the page containing a given address.
>  pub const PAGE_MASK: usize = !(PAGE_SIZE - 1);
>  
> +/// Round up the given number to a multiple of `PAGE_SIZE`.
> +pub fn page_align(addr: usize) -> usize {

Make it a `const` function? For example, there is a VMBUS_RING_SIZE()
macro in C that calculates a const number for a vmbus ringbuffer size,
so it will be useful.

> +    (addr + (PAGE_SIZE - 1)) & PAGE_MASK

I guess overflows are unexpected, i.e. the users should not pass a
`addr` that `> usize::MAX - PAGE_SIZE + 1`?

Regards,
Boqun

> +}
> +
>  /// A pointer to a page that owns the page allocation.
>  ///
>  /// # Invariants
> 
> ---
> base-commit: 8d8f785ceb21b9a0de11e05b811cc52d6fa79318
> change-id: 20241015-page-align-7e5fa4c751be
> 
> Best regards,
> -- 
> Alice Ryhl <aliceryhl@google.com>
>