Message-ID: <0dd770142c4757e1f94da6077345cc328de91fba.camel@redhat.com>
Date: Tue, 26 Aug 2025 17:01:34 -0400
From: Lyude Paul <lyude@...hat.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, 	acourbot@...dia.com, jgg@...pe.ca,
 robin.murphy@....com, 	daniel.almeida@...labora.com
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/5] Rust infrastructure for sg_table and scatterlist

For the whole series:

Reviewed-by: Lyude Paul <lyude@...hat.com>

Thanks for the wonderful work Danilo and Abdiel!

On Mon, 2025-08-25 at 15:24 +0200, Danilo Krummrich wrote:
> This patch series provides abstractions for struct sg_table and struct
> scatterlist.
> 
> Abdiel and me agreed for me to take over his previous iterations on this topic.
> I decided to send my patches as a new series rather than as a subsequent version
> of Abdiel's previous iterations, since the changes I made turned out to be much
> closer to a full rewrite.
> 
> The most notable differences in design are:
> 
>   - SGTable utilizes BorrowedPage, AsPageIter and VmallocPageIter from my patch
>     series in [1].
> 
>   -  SGTable is a transparent wrapper over either struct Owned<P> (where P is
>      the provider of the backing pages) or struct Borrowed, which by itself is a
>      transparent wrapper over Opaque<bindings::sg_table>, i.e. either
>      SGTable<Owned<P>> or just SGTable (which is equivalent to
>      SGTable<Borrowed>.
> 
>      - `SGTable<Owned<P>>`: Represents a table whose resources are fully managed
>        by Rust. It takes ownership of a page provider `P`, allocates the
>        underlying `struct sg_table`, maps it for DMA, and handles all cleanup
>        automatically upon drop. The DMA mapping's lifetime is tied to the
>        associated device using `Devres`, ensuring it is correctly unmapped
>        before the device is unbound.
> 
>      - `SGTable<Borrowed>` (or just `SGTable`): A zero-cost representation of an
>        externally managed `struct sg_table`. It is created from a raw pointer
>        using `SGTable::from_raw()` and provides a lifetime-bound reference
>        (`&'a SGTable`) for operations like iteration.
> 
>      - As a consequence, a borrowed SG table can be created with
>        SGTable::from_raw(), which returns a &'a SGTable, just like similar
>        existing abstractions.
> 
>        An owned SGTable is created with SGTable::new(), which returns an
>        impl PinInit<SGTable<Owned<P>>, Error>, such that it can be initialized
>        directly within existing private data memory allocations while providing
>        the required pin guarantees.
> 
>   - SGTable<Owned<P>> uses an inner type Devres<DmaMapSgt> to ensure that the
>     DMA mapping can't out-live device unbind.
> 
>   - SGTable<Owned<P>> uses pin-init for initialization.
> 
> This patch series depends on [1] (branch containing the patches in [2]). A
> branch containing this series (including dependencies) can be found in [3];
> Abdiel's latest series can be found in [4].
> 
> [1] https://lore.kernel.org/rust-for-linux/20250820145434.94745-1-dakr@kernel.org/
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=page-iter
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=scatterlist
> [4] https://lore.kernel.org/lkml/20250718103359.1026240-1-abdiel.janulgue@gmail.com/
> 
> Changes in v3:
>   - Beautify max_segment assignment code.
>   - Rename DmaMapSg to DmaMappedSg and improve documentation.
>   - Rename SGTable::as_iter() into SGTable::iter() and remove IntoIterator impl.
>   - Consider struct sg_table::nents in SGTable::iter() and SGTableIter<'_>.
> 
> Changes in v2:
>   - Switch to an enum impl for DmaDirection utilizing compile time boundary
>     checks.
>   - Add missing Send/ Sync impls.
>   - Rename as_ref() to from_raw().
>   - Add a bunch of inline annotations.
>   - Add a patch to introduce a typedef for dma_addr_t.
>   - Let dma_len() return ResourceSize.
>   - Add addional invariant to DmaMapSgt.
>   - In RawSGTable::new(), pass pages as mutable slice reference.
>   - Avoid casts when deriving max_segment in Owned::new().
> 
> Danilo Krummrich (5):
>   rust: dma: implement DataDirection
>   rust: dma: add type alias for bindings::dma_addr_t
>   rust: scatterlist: Add abstraction for sg_table
>   samples: rust: dma: add sample code for SGTable
>   MAINTAINERS: rust: dma: add scatterlist files
> 
>  MAINTAINERS                     |   4 +-
>  drivers/gpu/nova-core/falcon.rs |   4 +-
>  rust/bindings/bindings_helper.h |   1 +
>  rust/helpers/helpers.c          |   1 +
>  rust/helpers/scatterlist.c      |  24 ++
>  rust/kernel/dma.rs              |  86 +++++-
>  rust/kernel/lib.rs              |   1 +
>  rust/kernel/scatterlist.rs      | 483 ++++++++++++++++++++++++++++++++
>  samples/rust/rust_dma.rs        |  35 ++-
>  9 files changed, 623 insertions(+), 16 deletions(-)
>  create mode 100644 rust/helpers/scatterlist.c
>  create mode 100644 rust/kernel/scatterlist.rs
> 
> 
> base-commit: 27941214d368f3c17ed26a72662fc453bcc81b9d

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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