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

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Message-ID: <CAH5fLgiEn27VMUfrXcidu0rUpM7MPZVCOjywa-vQBO7dOdQrRQ@mail.gmail.com>
Date: Wed, 22 Jan 2025 18:06:58 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, miguel.ojeda.sandonis@...il.com, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	netdev@...r.kernel.org, andrew@...n.ch, hkallweit1@...il.com, 
	tmgross@...ch.edu, ojeda@...nel.org, alex.gaynor@...il.com, 
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, a.hindborg@...sung.com, 
	anna-maria@...utronix.de, frederic@...nel.org, tglx@...utronix.de, 
	arnd@...db.de, jstultz@...gle.com, sboyd@...nel.org, mingo@...hat.com, 
	peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com
Subject: Re: [PATCH v8 4/7] rust: time: Add wrapper for fsleep function

On Wed, Jan 22, 2025 at 6:05 PM Gary Guo <gary@...yguo.net> wrote:
>
> 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`).

It would need to use ..= instead of .. to match the current check.

Alice