linux-kernel - Re: [PATCH v3 07/13] rust: init: add `PinnedDrop` trait and macros

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Date:   Thu, 30 Mar 2023 15:41:35 +0000
From:   Benno Lossin <y86-dev@...tonmail.com>
To:     Gary Guo <gary@...yguo.net>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        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
Subject: Re: [PATCH v3 07/13] rust: init: add `PinnedDrop` trait and macros

On 30.03.23 13:01, Gary Guo wrote:
> On Wed, 29 Mar 2023 22:33:24 +0000
> y86-dev@...tonmail.com wrote:
>
>> From: Benno Lossin <y86-dev@...tonmail.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@...yguo.net>
>> Signed-off-by: Gary Guo <gary@...yguo.net>
>> Signed-off-by: Benno Lossin <y86-dev@...tonmail.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`.
Not really a good reason, I associate `new()` with 'unburdened' creation
(i.e. a safe function). Will change this.

--
Cheers,
Benno

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