linux-kernel - Re: [PATCH v2 1/2] rust: add initial scatterlist bindings

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Message-ID: <0206a7fa-ce7f-46af-8f1d-f9dedbb0a3d8@gmail.com>
Date: Wed, 9 Jul 2025 14:59:03 +0300
From: Abdiel Janulgue <abdiel.janulgue@...il.com>
To: Alexandre Courbot <acourbot@...dia.com>, jgg@...pe.ca, lyude@...hat.com,
 dakr@...nel.org
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Valentin Obst <kernel@...entinobst.de>,
 open list <linux-kernel@...r.kernel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Robin Murphy <robin.murphy@....com>, airlied@...hat.com,
 rust-for-linux@...r.kernel.org,
 "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
 Petr Tesarik <petr@...arici.cz>, Andrew Morton <akpm@...ux-foundation.org>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 Sui Jingfeng <sui.jingfeng@...ux.dev>, Randy Dunlap <rdunlap@...radead.org>,
 Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v2 1/2] rust: add initial scatterlist bindings

Hi,

On 03/07/2025 10:03, Alexandre Courbot wrote:
> On Wed Jul 2, 2025 at 11:37 AM JST, Alexandre Courbot wrote:
>> Thoughts? If Abdiel is comfortable with this I can submit a v3 with this design
>> for review (putting myself as co-developer), on which Abdiel could then keep
>> iterating, as I suspect this would be easier to understand than this long email
>> :).
> 
> Figured I could just as well share the code with you and save both of us
> some time. ^_^;
> 
> The top commit of this branch contains the proposal discussed:
> 
> https://github.com/Gnurou/linux/tree/scatterlists
> 
> The sample code has been updated to add dummy examples for the 3
> use-cases discussed (reference to an existing `sg_table`, refcounted
> reference, and owned data).
> 
> There are still things missing, including the typestate on `SGEntry`, as
> it wasn't necessary to demonstrate the basic idea.
> 
> Note also that if we decide to only support DMA-mapped SG-entries, we
> can remove a bunch of code, including the one that maps a `SGTable` if
> the backing type implements `BorrowMut`.
> 
> For your consideration. :) Please feel free to take and use anything you
> find useful.

Sorry for the delay, just came back from a week vacation.

Regarding your question regarding why I dropped type-state, I thought 
the general consensus here is to drop this approach:

https://lore.kernel.org/lkml/DAC20AXGABW2.X147X4JPMRBS@nvidia.com/

I think I might have misunderstood after re-reading it now. What you 
probably meant was to have no intermediate state from initialized to 
mapped to create the sg_table?

Anyways, thanks for the code above I'll look into this in detail and 
pick bits to integrate into v3 :)

/Abdiel