linux-kernel - Re: [PATCH v3 13/13] rust: sync: add functions for initializing `UniqueArc<MaybeUninit<T>>`

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Message-ID: <87v8ih1329.fsf@metaspace.dk>
Date:   Fri, 31 Mar 2023 15:07:18 +0200
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     y86-dev@...tonmail.com
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Alice Ryhl <alice@...l.io>, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        Andreas Hindborg <a.hindborg@...sung.com>
Subject: Re: [PATCH v3 13/13] rust: sync: add functions for initializing
 `UniqueArc<MaybeUninit<T>>`


y86-dev@...tonmail.com writes:

> From: Benno Lossin <y86-dev@...tonmail.com>
>
> Add two functions `init_with` and `pin_init_with` to
> `UniqueArc<MaybeUninit<T>>` to initialize the memory of already allocated
> `UniqueArc`s. This is useful when you want to allocate memory check some
> condition inside of a context where allocation is forbidden and then
> conditionally initialize an object.
>
> Signed-off-by: Benno Lossin <y86-dev@...tonmail.com>
> ---

Reviewed-by: Andreas Hindborg <a.hindborg@...sung.com>

>  rust/kernel/sync/arc.rs | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 4ed6329a5e5f..64b0e9d67025 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -540,6 +540,30 @@ impl<T> UniqueArc<MaybeUninit<T>> {
>              inner: unsafe { Arc::from_inner(inner.cast()) },
>          }
>      }
> +
> +    /// Initialize `self` using the given initializer.
> +    pub fn init_with<E>(mut self, init: impl Init<T, E>) -> core::result::Result<UniqueArc<T>, E> {
> +        // SAFETY: The supplied pointer is valid for initialization.
> +        match unsafe { init.__init(self.as_mut_ptr()) } {
> +            // SAFETY: Initialization completed successfully.
> +            Ok(()) => Ok(unsafe { self.assume_init() }),
> +            Err(err) => Err(err),
> +        }
> +    }
> +
> +    /// Pin-initialize `self` using the given pin-initializer.
> +    pub fn pin_init_with<E>(
> +        mut self,
> +        init: impl PinInit<T, E>,
> +    ) -> core::result::Result<Pin<UniqueArc<T>>, E> {
> +        // SAFETY: The supplied pointer is valid for initialization and we will later pin the value
> +        // to ensure it does not move.
> +        match unsafe { init.__pinned_init(self.as_mut_ptr()) } {
> +            // SAFETY: Initialization completed successfully.
> +            Ok(()) => Ok(unsafe { self.assume_init() }.into()),
> +            Err(err) => Err(err),
> +        }
> +    }
>  }
>
>  impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {