linux-kernel - Re: [PATCH net-next v3 4/8] rust: time: Implement addition of Ktime and Delta

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Message-ID: <CANiq72kWH8dGfnzB-wKk93NJY+k3vFSz-Z+bkPCdoehqEzFojA@mail.gmail.com>
Date: Thu, 17 Oct 2024 20:58:48 +0200
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, netdev@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, andrew@...n.ch, hkallweit1@...il.com, 
	tmgross@...ch.edu, ojeda@...nel.org, alex.gaynor@...il.com, gary@...yguo.net, 
	bjorn3_gh@...tonmail.com, benno.lossin@...ton.me, a.hindborg@...sung.com, 
	aliceryhl@...gle.com, anna-maria@...utronix.de, frederic@...nel.org, 
	tglx@...utronix.de, arnd@...db.de, jstultz@...gle.com, sboyd@...nel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/8] rust: time: Implement addition of Ktime
 and Delta

On Thu, Oct 17, 2024 at 7:03 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> but one thing I'm not sure is since it looks like saturating to
> KTIME_SEC_MAX is the current C choice, if we want to do the same, should
> we use the name `add_safe()` instead of `saturating_add()`? FWIW, it
> seems harmless to saturate at KTIME_MAX to me. So personally, I like

Wait -- `ktime_add_safe()` calls `ktime_set(KTIME_SEC_MAX, 0)` which
goes into the conditional that returns `KTIME_MAX`, not `KTIME_SEC_MAX
* NSEC_PER_SEC` (which is what I guess you were saying).

So I am confused -- it doesn't saturate to `KTIME_SEC_MAX` (scaled)
anyway. Which is confusing in itself.

In fact, it means that `ktime_add_safe()` allows you to get any value
whatsoever as long as you don't overflow, but `ktime_set` does not
allow you to -- unless you use enough nanoseconds to get you there
(i.e. over a second in nanoseconds).

Cheers,
Miguel