linux-kernel - Re: [PATCH] rust: page: add Rust version of PAGE

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Message-ID: <Zw61edSZrAb8pH1X@boqun-archlinux>
Date: Tue, 15 Oct 2024 11:33:29 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>, linux-mm@...ck.org,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: page: add Rust version of PAGE_ALIGN

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@...gle.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@...gle.com>
>