linux-kernel - Re: [PATCH v3 05/13] rust: init: add initialization macros

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Date:   Thu, 30 Mar 2023 16:21:37 +0200
From:   Alice Ryhl <alice@...l.io>
To:     y86-dev@...tonmail.com
Cc:     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 05/13] rust: init: add initialization macros

On 3/30/23 00:33, y86-dev@...tonmail.com wrote:
> From: Benno Lossin <y86-dev@...tonmail.com>
> 
> Add the following initializer macros:
> - `#[pin_data]` to annotate structurally pinned fields of structs,
>    needed for `pin_init!` and `try_pin_init!` to select the correct
>    initializer of fields.
> - `pin_init!` create a pin-initializer for a struct with the
>    `Infallible` error type.
> - `try_pin_init!` create a pin-initializer for a struct with a custom
>    error type (`kernel::error::Error` is the default).
> - `init!` create an in-place-initializer for a struct with the
>    `Infallible` error type.
> - `try_init!` create an in-place-initializer for a struct with a custom
>    error type (`kernel::error::Error` is the default).
> 
> Also add their needed internal helper traits and structs.
> 
> 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>

> +/// ```rust
> +/// # #![allow(clippy::disallowed_names, clippy::new_ret_no_self)]
> +/// # use kernel::{init, pin_init, prelude::*, init::*};
> +/// # use core::pin::Pin;
> +/// # #[pin_data]
> +/// # struct Foo {
> +/// #     a: usize,
> +/// #     b: Bar,
> +/// # }
> +/// # #[pin_data]
> +/// # struct Bar {
> +/// #     x: u32,
> +/// # }
> +///
> +/// impl Foo {
> +///     fn new() -> impl PinInit<Self> {

I would remove the empty line above `impl Foo` so that the example 
doesn't start with an empty line when rendered.

> +/// # Syntax
> +///
> +/// As already mentioned in the examples above, inside of `pin_init!` a `struct` initializer with
> +/// the following modifications is expected:
> +/// - Fields that you want to initialize in-place have to use `<-` instead of `:`.
> +/// - In front of the initializer you can write `&this in` to have access to a [`NonNull<Self>`]
> +///   pointer named `this` inside of the initializer.
> +///
> +/// For instance:
> +///
> +/// ```rust
> +/// # use kernel::pin_init;
> +/// # use macros::pin_data;
> +/// # use core::{ptr::addr_of_mut, marker::PhantomPinned};
> +/// #[pin_data]
> +/// struct Buf {
> +///     ptr: *mut u8,

I'd add a comment on the `ptr` field saying "points at `buf`".

> +/// impl BigBuf {
> +///     fn new() -> impl PinInit<Self, Error> {
> +///         try_pin_init!(Self {
> +///             big: {
> +///                 let zero = Box::try_new_zeroed()?;
> +///                 unsafe { zero.assume_init() }
> +///             },

Is there a reason for not using `Box::init(kernel::init::zeroed())?` here?