Re: [PATCH v3] rust: adding UniqueRefCounted and UniqueRef types

[Andreas Hindborg <a.hindborg@kernel.org>]

"Oliver Mangold" <oliver.mangold@pm.me> writes:

> From: Oliver Mangold <oliver.mangold@pm.me>
> Date: Fri, 21 Feb 2025 08:36:46 +0100
> Subject: [PATCH] rust: adding UniqueRefCounted and UniqueRef types
>
> Add `UniqueRef` as a variant of `ARef` that is guaranteed to be unique.
> This is useful when mutable access to the underlying type is required
> and we can guarantee uniqueness, and when APIs that would normally take
> an `ARef` require uniqueness.
>
> Signed-off-by: Oliver Mangold <oliver.mangold@pm.me>


This part:


    This should address all issues that have been raised with v2:

    - Added a default implementation for unique_to_shared() which does a simple
      rewrap of the underlying object.
    - Added a SimpleUniqueRefCounted trait which requires only to implement
      is_unique() as Benoît asked for. Maybe the feature is not worth
      the extra code, though. For me keeping it or removing would be both fine.
    - Removed the unsound conversion from &T to UniqueRef, as spotted by Benoît.
    - Relaxed the requirements for Send and Sync, to be identical to the ones
      for Box. See comment below.
    - Added Examples for both UniqueRefCounted and SimpleUniqueRefCounted
      as asked for by Boqun Feng.
      For me they compile and run without errors as KUnits.
    - Changed the commit message like suggested by Andreas.

    @Benoît: I think you are right about Send and Sync.
    What gave me a bit of a headache is if Send really does not require
    the underlying object to be Sync, as the refcount itself -
    which is part of the object - might be touched concurrently in a case
    like with tag_to_req(), but I think one would not implement
    something like that without having a synchronized refcount.

    Best regards,

    Oliver


Goes immedieatly after the cut like so:


    From: Oliver Mangold <oliver.mangold@pm.me>
    Date: Fri, 21 Feb 2025 08:36:46 +0100
    Subject: [PATCH] rust: adding UniqueRefCounted and UniqueRef types

    Add `UniqueRef` as a variant of `ARef` that is guaranteed to be unique.
    This is useful when mutable access to the underlying type is required
    and we can guarantee uniqueness, and when APIs that would normally take
    an `ARef` require uniqueness.

    Signed-off-by: Oliver Mangold <oliver.mangold@pm.me>
    ---


    This should address all issues that have been raised with v2:

    - Added a default implementation for unique_to_shared() which does a simple
      rewrap of the underlying object.
    - Added a SimpleUniqueRefCounted trait which requires only to implement
      is_unique() as Benoît asked for. Maybe the feature is not worth
      the extra code, though. For me keeping it or removing would be both fine.
    - Removed the unsound conversion from &T to UniqueRef, as spotted by Benoît.
    - Relaxed the requirements for Send and Sync, to be identical to the ones
      for Box. See comment below.
    - Added Examples for both UniqueRefCounted and SimpleUniqueRefCounted
      as asked for by Boqun Feng.
      For me they compile and run without errors as KUnits.
    - Changed the commit message like suggested by Andreas.

    @Benoît: I think you are right about Send and Sync.
    What gave me a bit of a headache is if Send really does not require
    the underlying object to be Sync, as the refcount itself -
    which is part of the object - might be touched concurrently in a case
    like with tag_to_req(), but I think one would not implement
    something like that without having a synchronized refcount.

    Best regards,

    Oliver

    ---

    rust/kernel/types.rs | 315 +++++++++++++++++++++++++++++++++++++++++++
    1 file changed, 315 insertions(+)


Again, I'll recommend the use of b4 [1].

Best regards,
Andreas Hindborg


[1] https://b4.docs.kernel.org/en/latest/contributor/prep.html