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Date:   Sat, 28 Jan 2023 12:14:29 +0100
Message-Id: <CQ3S2Z84SGAA.36ZVP0G4DF5VP@vincent>
To:     "Wedson Almeida Filho" <wedsonaf@gmail.com>,
        <rust-for-linux@vger.kernel.org>
Cc:     "Miguel Ojeda" <ojeda@kernel.org>,
        "Alex Gaynor" <alex.gaynor@gmail.com>,
        "Boqun Feng" <boqun.feng@gmail.com>, "Gary Guo" <gary@garyguo.net>,
        =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/5] rust: types: implement `ForeignOwnable` for the
 unit type
From:   "Vincenzo Palazzo" <vincenzopalazzodev@gmail.com>
References: <20230119174036.64046-1-wedsonaf@gmail.com>
 <20230119174036.64046-4-wedsonaf@gmail.com>
In-Reply-To: <20230119174036.64046-4-wedsonaf@gmail.com>
Precedence: bulk

On Thu Jan 19, 2023 at 6:40 PM CET, Wedson Almeida Filho 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>

> ---
>  rust/kernel/types.rs | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index e037c262f23e..8f80cffbff59 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -85,6 +85,19 @@ impl<T: 'static> ForeignOwnable for Box<T> {
>      }
>  }
> =20
> +impl ForeignOwnable for () {
> +    type Borrowed<'a> =3D ();
> +
> +    fn into_foreign(self) -> *const core::ffi::c_void {
> +        // We use 1 to be different from a null pointer.
> +        1usize as _
> +    }
> +
> +    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 f=
rom running.
> --=20
> 2.34.1