Date:   Mon, 30 Jan 2023 18:41:51 +0000
From:   Gary Guo <gary@garyguo.net>
To:     Wedson Almeida Filho <wedsonaf@gmail.com>
Cc:     rust-for-linux@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        =?UTF-8?B?QmrDtnJu?= Roy Baron <bjorn3_gh@protonmail.com>,
        linux-kernel@vger.kernel.org,
        Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Subject: Re: [PATCH v2 4/5] rust: types: implement `ForeignOwnable` for the
 unit type
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In-Reply-To: <20230130064404.744600-4-wedsonaf@gmail.com>
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        <20230130064404.744600-4-wedsonaf@gmail.com>
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On Mon, 30 Jan 2023 03:44:03 -0300
Wedson Almeida Filho <wedsonaf@gmail.com> wrote:

> This allows us to use the unit type `()` when we have no object whose
> ownership must be managed but one implementing the `ForeignOwnable`
> trait is needed.
> 
> Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
> Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
> v1 -> v2: use `NonNull::dangling` to generate pointer
> 
>  rust/kernel/types.rs | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 411655eca3e9..9d0fdbc55843 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -85,6 +85,18 @@ impl<T: 'static> ForeignOwnable for Box<T> {
>      }
>  }
>  
> +impl ForeignOwnable for () {
> +    type Borrowed<'a> = ();
> +
> +    fn into_foreign(self) -> *const core::ffi::c_void {
> +        core::ptr::NonNull::dangling().as_ptr()
> +    }
> +
> +    unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
> +
> +    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
> +}
> +
>  /// Runs a cleanup function/closure when dropped.
>  ///
>  /// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.