linux-kernel - Re: [PATCH net-next v2 2/6] rust: time: Introduce Delta type

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Message-Id: <20241009.230015.357430957218599542.fujita.tomonori@gmail.com>
Date: Wed, 09 Oct 2024 23:00:15 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: andrew@...n.ch
Cc: fujita.tomonori@...il.com, netdev@...r.kernel.org,
 rust-for-linux@...r.kernel.org, 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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/6] rust: time: Introduce Delta type

On Mon, 7 Oct 2024 15:33:13 +0200
Andrew Lunn <andrew@...n.ch> wrote:

>> I thought that from_secs(u16) gives long enough duration but
>> how about the following APIs?
>> 
>> pub fn from_nanos(nanos: u64)
>> pub fn from_micros(micros: u32)
>> pub fn from_millis(millis: u16) 
>> 
>> You can create the maximum via from_nanos. from_micros and from_millis
>> don't cause wrapping.
> 
> When i talked about transitive types, i was meaning that to_nanos(),
> to_micros(), to_millis() should have the same type as from_nanos(),
> to_micros(), and to_millis().
> 
> It is clear these APIs cause discard. millis is a lot less accurate
> than nanos. Which is fine, the names make that obvious. But what about
> the range? Are there values i can create using from_nanos() which i
> cannot then use to_millis() on because it overflows the u16? And i
> guess the overflow point is different to to_micros()? This API feels
> inconsistent to me. This is why i suggested u64 is used
> everywhere. And we avoid the range issues, by artificially clamping to
> something which can be represented in all forms, so we have a uniform
> behaviour.

I'll use u64 for all in v3; The range is to u64::MAX in nanoseconds
for all the from_* functions.