linux-kernel - Re: [PATCH v2 3/5] rust: scatterlist: Add type-state abstraction for sg

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Message-Id: <DC9UR87GP16E.2K9E9SSTHEBRB@nvidia.com>
Date: Sat, 23 Aug 2025 22:47:37 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>, <akpm@...ux-foundation.org>,
 <ojeda@...nel.org>, <alex.gaynor@...il.com>, <boqun.feng@...il.com>,
 <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>, <lossin@...nel.org>,
 <a.hindborg@...nel.org>, <aliceryhl@...gle.com>, <tmgross@...ch.edu>,
 <abdiel.janulgue@...il.com>, <jgg@...pe.ca>, <lyude@...hat.com>,
 <robin.murphy@....com>, <daniel.almeida@...labora.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] rust: scatterlist: Add type-state abstraction
 for sg_table

Oops, forgot to mention a couple more things:

On Thu Aug 21, 2025 at 1:52 AM JST, Danilo Krummrich wrote:
> Add a safe Rust abstraction for the kernel's scatter-gather list
> facilities (`struct scatterlist` and `struct sg_table`).
>
> This commit introduces `SGTable<T>`, a wrapper that uses a type-state
> pattern to provide compile-time guarantees about ownership and lifetime.

Is this actually a typestate? From my understanding, the typestate
pattern implies transitions from one state to the other (such as
Unmapped -> Mapped), but in this version there are no such transitions
(the previous ones had, though). We are just using a generic parameter,
so mentioning typestate sounds a bit misleading to me.

Another random thought, in the owned case, do we want to provide an
accessor to the provider of the backing pages? Or do we expect the
caller to take dispositions to keep such a reference if they need to
access the backing buffer post-mapping?