netdev - Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

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Message-Id: <20250118.170224.1577745251770787347.fujita.tomonori@gmail.com>
Date: Sat, 18 Jan 2025 17:02:24 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: miguel.ojeda.sandonis@...il.com
Cc: fujita.tomonori@...il.com, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

On Fri, 17 Jan 2025 19:59:15 +0100
Miguel Ojeda <miguel.ojeda.sandonis@...il.com> wrote:

> On Thu, Jan 16, 2025 at 5:42 AM FUJITA Tomonori
> <fujita.tomonori@...il.com> wrote:
>>
>> +/// `delta` must be 0 or greater and no more than `u32::MAX / 2` microseconds.
>> +/// If a value outside the range is given, the function will sleep
>> +/// for `u32::MAX / 2` microseconds (= ~2147 seconds or ~36 minutes) at least.
> 
> I would emphasize with something like:
> 
>     `delta` must be within [0, `u32::MAX / 2`] microseconds;
> otherwise, it is erroneous behavior. That is, it is considered a bug
> to call this function with an out-of-range value, in which case the
> function will sleep for at least the maximum value in the range and
> may warn in the future.

Thanks, I'll use the above instead.

> In addition, I would add a new paragraph how the behavior differs
> w.r.t. the C `fsleep()`, i.e. IIRC from the past discussions,
> `fsleep()` would do an infinite sleep instead. So I think it is
> important to highlight that.

/// The above behavior differs from the kernel's [`fsleep`], which could sleep
/// infinitely (for [`MAX_JIFFY_OFFSET`] jiffies).

Looks ok?

>> +    // The argument of fsleep is an unsigned long, 32-bit on 32-bit architectures.
>> +    // Considering that fsleep rounds up the duration to the nearest millisecond,
>> +    // set the maximum value to u32::MAX / 2 microseconds.
> 
> Nit: please use Markdown code spans in normal comments (no need for
> intra-doc links there).

Understood.

>> +    let duration = if delta > MAX_DURATION || delta.is_negative() {
>> +        // TODO: add WARN_ONCE() when it's supported.
> 
> Ditto (also "Add").

Oops, I'll fix.

> By the way, can this be written differently maybe? e.g. using a range
> since it is `const`?

A range can be used for a custom type?

> You can probably reuse `delta` as the new bindings name, since we
> don't need the old one after this step.

Do you mean something like the following?

const MAX_DELTA: Delta = Delta::from_micros(i32::MAX as i64);

let delta = if delta > MAX_DELTA || delta.is_negative() {
    // TODO: Add WARN_ONCE() when it's supported.
    MAX_DELTA
} else {
    delta
};