linux-kernel - Re: [PATCH v4 08/15] rust: init/sync: add `InPlaceInit` trait to pin-initialize smart pointers

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Message-ID: <ZCdh8fwSGTjDW6vE@boqun-archlinux>
Date:   Fri, 31 Mar 2023 15:42:57 -0700
From:   Boqun Feng <boqun.feng@...il.com>
To:     y86-dev@...tonmail.com
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...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>,
        Alice Ryhl <aliceryhl@...gle.com>
Subject: Re: [PATCH v4 08/15] rust: init/sync: add `InPlaceInit` trait to
 pin-initialize smart pointers

On Fri, Mar 31, 2023 at 09:53:25PM +0000, y86-dev@...tonmail.com wrote:
[...]
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index eee7008e5e3e..24dc96603090 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -17,6 +17,7 @@
> 
>  use crate::{
>      bindings,
> +    init::{InPlaceInit, Init, PinInit},
>      types::{ForeignOwnable, Opaque},
>  };
>  use alloc::boxed::Box;
> @@ -163,6 +164,28 @@ impl<T> Arc<T> {
>          // `Arc` object.
>          Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
>      }
> +
> +    /// Use the given initializer to in-place initialize a `T`.
> +    ///
> +    /// If `T: !Unpin` it will not be able to move afterwards.
> +    #[inline]
> +    pub fn pin_init<E>(init: impl PinInit<T, E>) -> Result<Self>

`Result` became `core::result::Result` after patch #3, so you will need
to refer to `crate::error::Result` here. Alternatively you can change
patch #3 to use the full path i.e. `core::result::Result`. 

> +    where
> +        Error: From<E>,

In my env, looks like the compiler doesn't know which `Error` it
is after removing use of `crate::error::Result` in patch #3, you
probably need to deal with this as well.

Regards,
Boqun

> +    {
> +        UniqueArc::pin_init(init).map(|u| u.into())
> +    }
> +
> +    /// Use the given initializer to in-place initialize a `T`.
> +    ///
> +    /// This is equivalent to [`pin_init`], since an [`Arc`] is always pinned.
> +    #[inline]
> +    pub fn init<E>(init: impl Init<T, E>) -> Result<Self>
> +    where
> +        Error: From<E>,
> +    {
> +        UniqueArc::init(init).map(|u| u.into())
> +    }
>  }
> 
>  impl<T: ?Sized> Arc<T> {
> --
> 2.39.2
> 
>