Re: [PATCH v5 21/38] rust: ptr: add const_align_up() and enable inline_const feature

[John Hubbard]

On 3/4/26 3:18 AM, Gary Guo wrote:
> On Wed Mar 4, 2026 at 3:47 AM GMT, John Hubbard wrote:
...
> The implementation doesn't address any of my original comment and all my points
> still apply.
> 

OK, so that implies that you want to return an Option, I believe,
like this?

commit b41512390999f85bcb2a3809c68f392e936b09ab
Author: John Hubbard <jhubbard@xxxxxxxxxx>
Date:   Thu Feb 19 14:44:02 2026 -0800

    rust: ptr: add const_align_up()
    
    Add const_align_up<ALIGN>() to kernel::ptr as the const-compatible
    equivalent of Alignable::align_up(). This uses inline_const to validate
    the alignment at compile time with a clear error message.
    
    Suggested-by: Danilo Krummrich <dakr@xxxxxxxxxx>
    Suggested-by: Gary Guo <gary@xxxxxxxxxxx>
    Suggested-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
    Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>

diff --git a/rust/kernel/ptr.rs b/rust/kernel/ptr.rs
index 5b6a382637fe..7e86429a9cb5 100644
--- a/rust/kernel/ptr.rs
+++ b/rust/kernel/ptr.rs
@@ -225,3 +225,29 @@ fn align_up(self, alignment: Alignment) -> Option<Self> {
 }
 
 impl_alignable_uint!(u8, u16, u32, u64, usize);
+
+/// Aligns `value` up to `ALIGN` at compile time.
+///
+/// This is the const-compatible equivalent of [`Alignable::align_up`].
+/// `ALIGN` must be a power of two (enforced at compile time).
+///
+/// Returns [`None`] on overflow.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::ptr::const_align_up;
+/// use kernel::sizes::SZ_4K;
+///
+/// assert_eq!(const_align_up::<16>(0x4f), Some(0x50));
+/// assert_eq!(const_align_up::<16>(0x40), Some(0x40));
+/// assert_eq!(const_align_up::<SZ_4K>(1), Some(SZ_4K));
+/// ```
+#[inline(always)]
+pub const fn const_align_up<const ALIGN: usize>(value: usize) -> Option<usize> {
+    const { assert!(ALIGN.is_power_of_two(), "ALIGN must be a power of two") };
+    match value.checked_add(ALIGN - 1) {
+        Some(v) => Some(v & !(ALIGN - 1)),
+        None => None,
+    }
+}


thanks,
-- 
John Hubbard