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

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Message-Id: <DC9VNDN0HLMX.PRFLKH5J3SCU@nvidia.com>
Date: Sat, 23 Aug 2025 23:29:37 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>
Cc: <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>, <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

On Sat Aug 23, 2025 at 11:20 PM JST, Danilo Krummrich wrote:
> On Sat Aug 23, 2025 at 4:16 PM CEST, Alexandre Courbot wrote:
>> On Sat Aug 23, 2025 at 10:57 PM JST, Danilo Krummrich wrote:
>>> On Sat Aug 23, 2025 at 3:47 PM CEST, Alexandre Courbot wrote:
>>>> 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.
>>>
>>> I'd argue that it's still kind of a typestate. You can derive &SGTable (i.e.
>>> &SGTable<Borrowed>) from SGTabe<Owned>. So, technically there is an
>>> uni-directional transition I guess.
>>
>> That's technically correct, but is also not the intent of the design, at
>> least compared to something like Unmapped <-> Mapped. Not a big problem
>> if you prefer to keep the current naming though.
>
> I don't mind to name / call it differently, any suggestion?

Simply using "generic parameter" would lift the possiblity for
misinterpretation IMHO.