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Message-ID: <20230816184324.41a91d73.gary@garyguo.net>
Date: Wed, 16 Aug 2023 18:43:24 +0100
From: Gary Guo <gary@...yguo.net>
To: Benno Lossin <benno.lossin@...ton.me>,
Asahi Lina <lina@...hilina.net>
Cc: Miguel Ojeda <ojeda@...nel.org>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Alice Ryhl <aliceryhl@...gle.com>,
Andreas Hindborg <nmi@...aspace.dk>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
patches@...ts.linux.dev,
Martin Rodriguez Reboredo <yakoyoku@...il.com>
Subject: Re: [PATCH v4 08/13] rust: init: Add functions to create array
initializers
On Mon, 14 Aug 2023 08:47:15 +0000
Benno Lossin <benno.lossin@...ton.me> wrote:
> Add two functions `pin_init_array_from_fn` and `init_array_from_fn` that
> take a function that generates initializers for `T` from usize, the added
> functions then return an initializer for `[T; N]` where every element is
> initialized by an element returned from the generator function.
>
> Suggested-by: Asahi Lina <lina@...hilina.net>
> Reviewed-by: Björn Roy Baron <bjorn3_gh@...tonmail.com>
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
> ---
> v3 -> v4:
> - changed example size from 1_000_000_000 to 1_000,
> - made functions unwind-safe by using a ScopeGuard,
> - added Reviewed-by from Martin.
>
> v2 -> v3:
> - changed doctest: instead of printing the array, assert the length,
> - added Reviewed-by's from Alice.
>
> v1 -> v2:
> - fix warnings and errors in doctests,
> - replace dropping loop with `drop_in_place` and `slice_from_raw_parts_mut`
> inside of `{pin_}init_array_from_fn` functions.
>
> rust/kernel/init.rs | 88 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 88 insertions(+)
>
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index 460f808ebf84..b54f32017d00 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -212,6 +212,7 @@
> use crate::{
> error::{self, Error},
> sync::UniqueArc,
> + types::ScopeGuard,
> };
> use alloc::boxed::Box;
> use core::{
> @@ -875,6 +876,93 @@ pub fn uninit<T, E>() -> impl Init<MaybeUninit<T>, E> {
> unsafe { init_from_closure(|_| Ok(())) }
> }
>
> +/// Initializes an array by initializing each element via the provided initializer.
> +///
> +/// # Examples
> +///
> +/// ```rust
> +/// use kernel::{error::Error, init::init_array_from_fn};
> +/// let array: Box<[usize; 1_000]>= Box::init::<Error>(init_array_from_fn(|i| i)).unwrap();
> +/// assert_eq!(array.len(), 1_000);
> +/// ```
> +pub fn init_array_from_fn<I, const N: usize, T, E>(
> + mut make_init: impl FnMut(usize) -> I,
> +) -> impl Init<[T; N], E>
> +where
> + I: Init<T, E>,
> +{
> + let init = move |slot: *mut [T; N]| {
> + let slot = slot.cast::<T>();
> + // Counts the number of initialized elements and when dropped drops that many elements from
> + // `slot`.
> + let mut init_count = ScopeGuard::new_with_data(0, |i| {
> + // We now free every element that has been initialized before:
> + // SAFETY: The loop initialized exactly the values from 0..i and since we
> + // return `Err` below, the caller will consider the memory at `slot` as
> + // uninitialized.
> + unsafe { ptr::drop_in_place(ptr::slice_from_raw_parts_mut(slot, i)) };
> + });
> + for i in 0..N {
> + let init = make_init(i);
> + // SAFETY: since 0 <= `i` < N, it is still in bounds of `[T; N]`.
> + let ptr = unsafe { slot.add(i) };
> + // SAFETY: The pointer is derived from `slot` and thus satisfies the `__init`
> + // requirements.
> + unsafe { init.__init(ptr) }?;
> + *init_count += 1;
> + }
> + init_count.dismiss();
> + Ok(())
> + };
> + // SAFETY: The initializer above initializes every element of the array. On failure it drops
> + // any initialized elements and returns `Err`.
> + unsafe { init_from_closure(init) }
> +}
> +
> +/// Initializes an array by initializing each element via the provided initializer.
> +///
> +/// # Examples
> +///
> +/// ```rust
> +/// use kernel::{sync::{Arc, Mutex}, init::pin_init_array_from_fn, new_mutex};
> +/// let array: Arc<[Mutex<usize>; 1_000]>=
> +/// Arc::pin_init(pin_init_array_from_fn(|i| new_mutex!(i))).unwrap();
> +/// assert_eq!(array.len(), 1_000);
> +/// ```
> +pub fn pin_init_array_from_fn<I, const N: usize, T, E>(
> + mut make_init: impl FnMut(usize) -> I,
> +) -> impl PinInit<[T; N], E>
> +where
> + I: PinInit<T, E>,
> +{
> + let init = move |slot: *mut [T; N]| {
> + let slot = slot.cast::<T>();
> + // Counts the number of initialized elements and when dropped drops that many elements from
> + // `slot`.
> + let mut init_count = ScopeGuard::new_with_data(0, |i| {
> + // We now free every element that has been initialized before:
> + // SAFETY: The loop initialized exactly the values from 0..i and since we
> + // return `Err` below, the caller will consider the memory at `slot` as
> + // uninitialized.
> + unsafe { ptr::drop_in_place(ptr::slice_from_raw_parts_mut(slot, i)) };
> + });
> + for i in 0..N {
> + let init = make_init(i);
> + // SAFETY: since 0 <= `i` < N, it is still in bounds of `[T; N]`.
> + let ptr = unsafe { slot.add(i) };
> + // SAFETY: The pointer is derived from `slot` and thus satisfies the `__init`
> + // requirements.
> + unsafe { init.__pinned_init(ptr) }?;
> + *init_count += 1;
> + }
> + init_count.dismiss();
> + Ok(())
> + };
> + // SAFETY: The initializer above initializes every element of the array. On failure it drops
> + // any initialized elements and returns `Err`.
> + unsafe { pin_init_from_closure(init) }
> +}
> +
I wonder instead of two nearly identical function, whether this could
be a single type that returns a struct which is Init if the initializer
is (would need patch 11).
> // SAFETY: Every type can be initialized by-value.
> unsafe impl<T, E> Init<T, E> for T {
> unsafe fn __init(self, slot: *mut T) -> Result<(), E> {
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