linux-kernel - Re: [PATCH 1/4] rust: alloc: implement `Borrow` and `BorrowMut` for `Vec`

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Message-Id: <DABND24P80ZZ.NLCKU3AYPN4X@nvidia.com>
Date: Mon, 02 Jun 2025 10:13:22 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Benno Lossin" <lossin@...nel.org>, "Danilo Krummrich"
 <dakr@...nel.org>, "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>, "Andreas Hindborg" <a.hindborg@...nel.org>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>
Cc: <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] rust: alloc: implement `Borrow` and `BorrowMut` for
 `Vec`

Hi Benno,

On Mon Jun 2, 2025 at 1:11 AM JST, Benno Lossin wrote:
> On Sun Jun 1, 2025 at 5:00 AM CEST, Alexandre Courbot wrote:
>> Implement these two common traits, which allow generic types to store
>> either an owned value or a reference to it.
>
> I don't understand the second part of the sentence.

I want to say that Borrow allows you to do something like:

    struct Foo<B: Borrow<u32>>(B);

    // `foo1` owns its value...
    let foo1 = Foo(0x12);

    let i = 0x24;
    // ... but `foo2` just borrows it, subject to the lifetime of `i`.
    let foo2 = Foo(&i);

And the implementations in this series also let you do:

    // `foo3`'s value is owned, but heap-allocated
    let foo3 = Arc::new(KBox::new(0x56, GFP_KERNEL)?);

    let j = Arc::new(0x78, GFP_KERNEL)?;
    // `foo4`'s value is shared and its lifetime runtime-managed.
    let foo4 = Foo(j.clone());