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Date: Sat, 24 Jun 2023 09:25:34 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Miguel Ojeda <ojeda@...nel.org>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Alex Gaynor <alex.gaynor@...il.com>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
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, Asahi Lina <lina@...hilina.net>
Subject: [PATCH 6/7] rust: init: Add functions to create array initializers
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>
Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
---
rust/kernel/init.rs | 90 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 90 insertions(+)
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 44bc3e77419a..c9ea4bf71987 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -867,6 +867,96 @@ 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
+/// let array: Box<[usize; 1000_000_000]>= Box::init(init_array_from_fn(|i| i)).unwrap();
+/// println!("{array:?}");
+/// ```
+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>();
+ 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.
+ match unsafe { init.__init(ptr) } {
+ Ok(()) => {}
+ Err(e) => {
+ // We now free every element that has been initialized before:
+ for j in 0..i {
+ let ptr = unsafe { slot.add(j) };
+ // SAFETY: The value was initialized in a previous iteration of the loop
+ // and since we return `Err` below, the caller will consider the memory at
+ // `slot` as uninitialized.
+ unsafe { ptr::drop_in_place(ptr) };
+ }
+ return Err(e);
+ }
+ }
+ }
+ 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
+/// let array: Arc<[Mutex<usize>; 1000_000_000]>=
+/// Arc::pin_init(init_array_from_fn(|i| new_mutex!(i))).unwrap();
+/// println!("{array:?}");
+/// ```
+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>();
+ 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 `__pinned_init`
+ // requirements.
+ match unsafe { init.__pinned_init(ptr) } {
+ Ok(()) => {}
+ Err(e) => {
+ // We now have to free every element that has been initialized before, since we
+ // have to abide by the drop guarantee.
+ for j in 0..i {
+ let ptr = unsafe { slot.add(j) };
+ // SAFETY: The value was initialized in a previous iteration of the loop
+ // and since we return `Err` below, the caller will consider the memory at
+ // `slot` as uninitialized.
+ unsafe { ptr::drop_in_place(ptr) };
+ }
+ return Err(e);
+ }
+ }
+ }
+ 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) }
+}
+
// 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> {
--
2.41.0
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