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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <54924687-4634-4a41-9f0f-f052ac34e1bf@lunn.ch>
Date: Mon, 7 Oct 2024 15:33:13 +0200
From: Andrew Lunn <andrew@...n.ch>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: 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

> 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.

But i have little experience of dealing with time in the kernel. I
don't know what the real issues are here, what developers have been
getting wrong for the last 30 years etc.

	Andrew