Re: [PATCH 02/10] rust: alloc: introduce the `VecExt` trait

Benno Lossin
2024-03-25T22:05:56Z

On 25.03.24 20:54, Wedson Almeida Filho wrote:> From: Wedson Almeida Filho <walmeida@microsoft.com>
>
> Make `try_with_capacity`, `try_push`, and `try_extend_from_slice`
> methods available in `Vec` even though it doesn't implement them. It is
> implemented with `try_reserve` and `push_within_capacity`.
>
> This is in preparation for switching to the upstream `alloc` crate.
>
> Suggested-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
> rust/kernel/alloc.rs | 1 +
> rust/kernel/alloc/vecext.rs | 52 +++++++++++++++++++++++++++++++++++++
> rust/kernel/lib.rs | 1 +
> rust/kernel/prelude.rs | 2 ++
> 4 files changed, 56 insertions(+)
> create mode 100644 rust/kernel/alloc/vecext.rs
>
> diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
> index ccd4149932c3..8ad57a2e693e 100644
> --- a/rust/kernel/alloc.rs
> +++ b/rust/kernel/alloc.rs
> @@ -5,3 +5,4 @@
> #[cfg(not(test))]
> #[cfg(not(testlib))]
> mod allocator;
> +pub mod vecext;
> diff --git a/rust/kernel/alloc/vecext.rs b/rust/kernel/alloc/vecext.rs
> new file mode 100644
> index 000000000000..59e92bab534e
> --- /dev/null
> +++ b/rust/kernel/alloc/vecext.rs
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Extensions to [`Vec`] for fallible allocations.
> +
> +use alloc::{collections::TryReserveError, vec::Vec};
> +use core::result::Result;
> +
> +/// Extensions to [`Vec`].
> +pub trait VecExt<T>: Sized {
> + /// Creates a new [`Vec`] instance with at least the given capacity.
> + fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError>;
> +
> + /// Appends an element to the back of the [`Vec`] instance.
> + fn try_push(&mut self, v: T) -> Result<(), TryReserveError>;
> +
> + /// Pushes clones of the elements of slice into the [`Vec`] instance.
> + fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError>
> + where
> + T: Clone;

All of the non `try_` prefix functions require
`not(no_global_oom_handling)`, so we could also drop the `try_` prefix
here.
What do you think?

> +}
> +
> +impl<T> VecExt<T> for Vec<T> {
> + fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
> + let mut v = Vec::new();
> + v.try_reserve(capacity)?;
> + Ok(v)
> + }
> +
> + fn try_push(&mut self, v: T) -> Result<(), TryReserveError> {
> + if let Err(retry) = self.push_within_capacity(v) {
> + self.try_reserve(1)?;
> + let _ = self.push_within_capacity(retry);
> + }
> + Ok(())
> + }
> +
> + fn try_extend_from_slice(&mut self, other: &[T]) -> Result<(), TryReserveError>
> + where
> + T: Clone,
> + {
> + let extra_cap = self.capacity() - self.len();
> + if extra_cap > 0 {
> + self.try_reserve(extra_cap)?;
> + }

I am confused, why are you doing this? Did you mean to do this?:
let extra_cap = self.capacity() - self.len() - other.len();

--
Cheers,
Benno

> +
> + for item in other {
> + self.try_push(item.clone())?;
> + }
> +
> + Ok(())
> + }
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 51f30e55bd00..7f2841a18d05 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -19,6 +19,7 @@
> #![feature(offset_of)]
> #![feature(receiver_trait)]
> #![feature(unsize)]
> +#![feature(vec_push_within_capacity)]
>
> // Ensure conditional compilation based on the kernel configuration works;
> // otherwise we may silently break things like initcall handling.
> diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
> index ae21600970b3..a0177f195dec 100644
> --- a/rust/kernel/prelude.rs
> +++ b/rust/kernel/prelude.rs
> @@ -14,6 +14,8 @@
> #[doc(no_inline)]
> pub use core::pin::Pin;
>
> +pub use crate::alloc::vecext::VecExt;
> +
> #[doc(no_inline)]
> pub use alloc::{boxed::Box, vec::Vec};
>
> --
> 2.34.1
>