Re: [PATCH v2] rust: time: add Delta::to_jiffies_timeout() for timeout conversion

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Sep 07, 2026 at 09:35:24PM +0900, FUJITA Tomonori wrote:
> diff --git a/rust/helpers/math.c b/rust/helpers/math.c
> new file mode 100644
> index 000000000000..e2ee29bcce0f
> --- /dev/null
> +++ b/rust/helpers/math.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/math64.h>
> +
> +__rust_helper u64 rust_helper_mul_u64_add_u64_div_u64(u64 a, u64 b, u64 c, u64 d)
> +{
> +	return mul_u64_add_u64_div_u64(a, b, c, d);
> +}

This looks like it's never an inline function, so I don't think a helper
is needed.

> diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
> index 6c0a5e8090d0..8e9c349b1df7 100644
> --- a/rust/kernel/time.rs
> +++ b/rust/kernel/time.rs
> @@ -39,6 +39,10 @@
>  /// The number of nanoseconds per second.
>  pub const NSEC_PER_SEC: i64 = bindings::NSEC_PER_SEC as i64;
>  
> +/// The C side `MAX_JIFFY_OFFSET`, i.e. `((LONG_MAX >> 1) - 1)`. It is the upper
> +/// bound the kernel uses for a jiffies span, not a wait-forever value.
> +const MAX_JIFFY_OFFSET: isize = (isize::MAX >> 1) - 1;

Should this be:

const MAX_JIFFY_OFFSET: Jiffies = (isize::MAX >> 1) - 1;

The Jiffies type alias is always the same as isize, but it may be more
clear for readers to use Jiffies for the constant.

> +        // `bindings::HZ` cannot be used here. bindgen keeps the first definition of a
> +        // macro and ignores a later `#undef`, so `HZ` resolves to `__USER_HZ`, i.e.
> +        // 100, from `include/uapi/asm-generic/param.h` instead of `CONFIG_HZ`.
> +        const HZ: u64 = bindings::CONFIG_HZ as u64;

Sounds very error-prone. Consider fixing this in rust/bindings/lib.rs
similar to `compat_ptr_ioctl` and then use bindings::HZ here. This will
reduce the chance of others using bindings::HZ and getting the wrong
value.

Alice