netdev - Re: [PATCH net-next v3 1/3] rust: core abstractions for network PHY drivers

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Date: Fri, 13 Oct 2023 14:45:03 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: boqun.feng@...il.com
Cc: benno.lossin@...ton.me, fujita.tomonori@...il.com, tmgross@...ch.edu,
 netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, andrew@...n.ch,
 miguel.ojeda.sandonis@...il.com, greg@...ah.com
Subject: Re: [PATCH net-next v3 1/3] rust: core abstractions for network
 PHY drivers

On Thu, 12 Oct 2023 21:17:14 -0700
Boqun Feng <boqun.feng@...il.com> wrote:

> After re-read my email exchange with Tomo, I realised I need to explain
> this a little bit. The minimal requirement of a Rust binding is
> soundness: it means if one only uses safe APIs, one cannot introduce
> memory/type safety issue (i.e. cannot have an object in an invalid
> state), this is a tall task, because you can have zero assumption of the
> API users, you can only encode the usage requirement in the type system.
> 
> Of course the type system doesn't always work, hence we have unsafe API,
> but still the soundness of Rust bindings means using safe APIs +
> *correctly* using unsafe APIs cannot introduce memory/type safety
> issues.
> 
> Tomo, this is why we gave you a hard time here ;-) Unsafe Rust APIs must
> be very clear on the correct usage and safe Rust APIs must not assume
> how users would call it. Hope this help explain a little bit, we are not
> poking random things here, soundness is the team effort from everyone
> ;-)

Understood, so let me know if you still want to improve something in
v4 patchset :) I tried to addressed all the review comments.

btw, what's the purpose of using Rust in linux kernel? Creating sound
Rust abstractions? Making linux kernel more reliable, or something
else?  For me, making linux kernel more reliable is the whole
point. Thus I still can't understand the slogan that Rust abstractions
can't trust subsystems.

Rust abstractions always must check the validity of values that
subsysmtes give because subsysmtes might give an invalid value. Like
the enum state issue, if PHYLIB has a bug then give a random value, so
the abstraction have to prevent the invalid value in Rust with
validity checking. But with such critical bug, likely the system
cannot continue to run anyway. Preventing the invalid state in Rust
aren't useful much for system reliability.