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Date:   Thu, 30 Mar 2023 12:01:03 +0100
From:   Gary Guo <gary@garyguo.net>
To:     y86-dev@protonmail.com
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        =?UTF-8?B?QmrDtnJu?= Roy Baron <bjorn3_gh@protonmail.com>,
        Alice Ryhl <alice@ryhl.io>, rust-for-linux@vger.kernel.org,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
Subject: Re: [PATCH v3 07/13] rust: init: add `PinnedDrop` trait and macros
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On Wed, 29 Mar 2023 22:33:24 +0000
y86-dev@protonmail.com wrote:

> From: Benno Lossin <y86-dev@protonmail.com>
> 
> The `PinnedDrop` trait that facilitates destruction of pinned types.
> It has to be implemented via the `#[pinned_drop]` macro, since the
> `drop` function should not be called by normal code, only by other
> destructors. It also only works on structs that are annotated with
> `#[pin_data(PinnedDrop)]`.
> 
> Co-developed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Benno Lossin <y86-dev@protonmail.com>
> ---
>  rust/kernel/init.rs            | 111 ++++++++++++++
>  rust/kernel/init/__internal.rs |  15 ++
>  rust/kernel/init/macros.rs     | 263 +++++++++++++++++++++++++++++++++
>  rust/macros/lib.rs             |  49 ++++++
>  rust/macros/pinned_drop.rs     |  49 ++++++
>  5 files changed, 487 insertions(+)
>  create mode 100644 rust/macros/pinned_drop.rs
> 
> diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal.rs
> index 692942a008b3..4a3c7bf27a06 100644
> --- a/rust/kernel/init/__internal.rs
> +++ b/rust/kernel/init/__internal.rs
> @@ -132,3 +132,18 @@ impl<T: ?Sized> Drop for DropGuard<T> {
>          }
>      }
>  }
> +
> +/// Token used by `PinnedDrop` to prevent calling the function without creating this unsafely
> +/// created struct. This is needed, because the `drop` function is safe, but should not be called
> +/// manually.
> +pub struct OnlyCallFromDrop(());
> +
> +impl OnlyCallFromDrop {
> +    /// # Safety
> +    ///
> +    /// This function should only be called from the [`Drop::drop`] function and only be used to
> +    /// delegate the destruction to the pinned destructor [`PinnedDrop::drop`] of the same type.
> +    pub unsafe fn create() -> Self {

Although this is impl detail and the name doesn't really matter, but I
am wondering why this is called `create` instead of just `new`.

> +        Self(())
> +    }
> +}