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

[FUJITA Tomonori <tomo@flapping.org>]

On Tue, 8 Sep 2026 12:45:58 +0000
Alice Ryhl <aliceryhl@google.com> wrote:

> 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.

It's an inline function on x86; arch/x86/include/asm/div64.h.


>> 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.

Jiffies is crate::ffi::c_ulong, i.e. usize, not isize. And it will be
removed; replacing it with Delta<Jiffy> is what the series is for

https://lore.kernel.org/rust-for-linux/20260808062839.1159990-8-tomo@flapping.org/


>> +        // `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.

Good idea, thanks. I'll do that in v3: patch 1 fixes bindings::HZ in lib.rs,
and this patch then uses it.