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

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Message-ID: <20250122170537.1a92051c.gary@garyguo.net>
Date: Wed, 22 Jan 2025 17:05:37 +0000
From: Gary Guo <gary@...yguo.net>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: miguel.ojeda.sandonis@...il.com, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, netdev@...r.kernel.org, andrew@...n.ch,
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Subject: Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

On Sat, 18 Jan 2025 17:02:24 +0900 (JST)
FUJITA Tomonori <fujita.tomonori@...il.com> wrote:

> 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?

Yes, you can say `!(Delta::ZERO..MAX_DURATION).contains(&delta)`.
(You'll need to add `Delta::ZERO`).

The `start..end` syntax is a fancy way of constructing a
`core::ops::Range` which has `contains` as long as `PartialOrd` is
implemented.

> 
> > 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
> };