linux-kernel - [PATCH v2] rust: page: add Rust version of PAGE

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Message-ID: <20241016-page-align-v2-1-e0afe85fc4b4@google.com>
Date: Wed, 16 Oct 2024 11:34:25 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...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, 
	Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v2] rust: page: add Rust version of PAGE_ALIGN

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@...il.com>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.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.
+    (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,
-- 
Alice Ryhl <aliceryhl@...gle.com>