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Date:   Thu, 30 Mar 2023 15:36:29 +0000
To:     Alice Ryhl <alice@ryhl.io>
From:   Benno Lossin <y86-dev@protonmail.com>
Cc:     rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@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>
Subject: Re: [PATCH v3 04/13] rust: add pin-init API core
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On 30.03.23 15:33, Alice Ryhl wrote:
> On 3/30/23 00:33, y86-dev@protonmail.com wrote:
>> From: Benno Lossin <y86-dev@protonmail.com>
>>
>> This API is used to facilitate safe pinned initialization of structs. It
>> replaces cumbersome `unsafe` manual initialization with elegant safe mac=
ro
>> invocations.
>>
>> Due to the size of this change it has been split into six commits:
>> 1. This commit introducing the basic public interface: traits and
>>      functions to represent and create initializers.
>> 2. Adds the `#[pin_data]`, `pin_init!`, `try_pin_init!`, `init!` and
>>      `try_init!` macros along with their internal types.
>> 3. Adds the `InPlaceInit` trait that allows using an initializer to crea=
te
>>      an object inside of a `Box<T>` and other smart pointers.
>> 4. Adds the `PinnedDrop` trait and adds macro support for it in
>>      the `#[pin_data]` macro.
>> 5. Adds the `stack_pin_init!` macro allowing to pin-initialize a struct =
on
>>      the stack.
>> 6. Adds the `Zeroable` trait and `init::zeroed` function to initialize
>>      types that have `0x00` in all bytes as a valid bit pattern.
>>
>> 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>
>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
>
>> +//! Aside from pinned initialization, this API also supports in-place c=
onstruction without pinning,
>> +//! the marcos/types/functions are generally named like the pinned vari=
ants without the `pin`
>> +//! prefix.
>
> Typo: Should be "macros".
>
>> +type Invariant<T> =3D PhantomData<fn(*mut T) -> *mut T>;
>
> I think it would make sense to include a link to the nomicon on the
> documentation for the Invariant type.
>
> E.g. this link: https://doc.rust-lang.org/nomicon/subtyping.html

Sure that is a good idea.

>> +// This is the module-internal type implementing `PinInit` and `Init`. =
It is unsafe to create this
>> +// type, since the closure needs to fulfill the same safety requirement=
 as the
>> +// `__pinned_init`/`__init` functions.
>> +struct InitClosure<F, T: ?Sized, E>(F, Invariant<(E, T)>);
>
> Documentation for a type should use /// rather than //.
>
> I think it would help to call out explicitly in the documentation on
> this type that it is an implementation detail of the
> pin_init_from_closure and init_from_closure methods.

Yeah, I will also move this into `__internal.rs` and add the comment.

--
Cheers,
Benno