linux-kernel - Re: [PATCH v3 04/13] rust: add pin-init API core

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Message-ID: <878rfe493r.fsf@metaspace.dk>
Date:   Thu, 30 Mar 2023 16:16:31 +0200
From:   Andreas Hindborg <nmi@...aspace.dk>
To:     Alice Ryhl <alice@...l.io>
Cc:     y86-dev@...tonmail.com, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        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>
Subject: Re: [PATCH v3 04/13] rust: add pin-init API core


Alice Ryhl <alice@...l.io> writes:

> On 3/30/23 00:33, y86-dev@...tonmail.com wrote:
>> From: Benno Lossin <y86-dev@...tonmail.com>
>> This API is used to facilitate safe pinned initialization of structs. It
>> replaces cumbersome `unsafe` manual initialization with elegant safe macro
>> 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 create
>>     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@...yguo.net>
>> Signed-off-by: Gary Guo <gary@...yguo.net>
>> Signed-off-by: Benno Lossin <y86-dev@...tonmail.com>
>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>
>> +//! Aside from pinned initialization, this API also supports in-place construction without pinning,
>> +//! the marcos/types/functions are generally named like the pinned variants without the `pin`
>> +//! prefix.
>
> Typo: Should be "macros".
>
>> +type Invariant<T> = 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

That would be nice. I think this also applies: https://doc.rust-lang.org/nomicon/phantom-data.html#table-of-phantomdata-patterns

>
>> +// 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.