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Date: Sat, 30 Mar 2024 13:35:04 +0000
To: Wedson Almeida Filho <wedsonaf@gmail.com>, rust-for-linux@vger.kernel.org
From: Benno Lossin <benno.lossin@proton.me>
Cc: Miguel Ojeda <ojeda@kernel.org>, Alex Gaynor <alex.gaynor@gmail.com>, Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>, =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, Andreas Hindborg <a.hindborg@samsung.com>, Alice Ryhl <aliceryhl@google.com>, linux-kernel@vger.kernel.org, Wedson Almeida Filho <walmeida@microsoft.com>
Subject: Re: [PATCH v3 06/10] rust: alloc: introduce the `BoxExt` trait
Message-ID: <6a684f4d-6f95-4c52-b515-73c832f050a8@proton.me>
In-Reply-To: <20240328013603.206764-7-wedsonaf@gmail.com>
References: <20240328013603.206764-1-wedsonaf@gmail.com> <20240328013603.206764-7-wedsonaf@gmail.com>
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On 28.03.24 02:35, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@microsoft.com>
>=20
> Make fallible versions of `new` and `new_uninit` methods available in
> `Box` even though it doesn't implement them because we build `alloc`
> with the `no_global_oom_handling` config.
>=20
> They also have an extra `flags` parameter that allows callers to pass
> flags to the allocator.
>=20
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
>   rust/kernel/alloc.rs           |  1 +
>   rust/kernel/alloc/allocator.rs |  2 +-
>   rust/kernel/alloc/box_ext.rs   | 60 ++++++++++++++++++++++++++++++++++
>   rust/kernel/init.rs            | 13 ++++----
>   rust/kernel/prelude.rs         |  2 +-
>   rust/kernel/sync/arc.rs        |  3 +-
>   6 files changed, 72 insertions(+), 9 deletions(-)
>   create mode 100644 rust/kernel/alloc/box_ext.rs

With Boqun's suggestion (feel free to take your variant):

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

[...]

> +impl<T> BoxExt<T> for Box<T> {
> +    fn new(x: T, flags: Flags) -> Result<Self, AllocError> {
> +        let mut b =3D <Self as BoxExt<_>>::new_uninit(flags)?;
> +        b.write(x);
> +        // SAFETY: The contents were just initialised in the line above.
> +        Ok(unsafe { b.assume_init() })
> +    }
> +
> +    #[cfg(any(test, testlib))]
> +    fn new_uninit(_flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocErr=
or> {
> +        Ok(Box::new_uninit())
> +    }
> +
> +    #[cfg(not(any(test, testlib)))]
> +    fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocErro=
r> {
> +        let ptr =3D if core::mem::size_of::<MaybeUninit<T>>() =3D=3D 0 {
> +            core::ptr::NonNull::<_>::dangling().as_ptr()
> +        } else {
> +            let layout =3D core::alloc::Layout::new::<MaybeUninit<T>>();
> +
> +            // SAFETY: Memory is being allocated (first arg is null). Th=
e only other source of
> +            // safety issues is sleeping on atomic context, which is add=
ressed by klint. Lastly,
> +            // the type is not a SZT (checked above).
> +            let ptr =3D
> +                unsafe { super::allocator::krealloc_aligned(core::ptr::n=
ull_mut(), layout, flags) };

Personally, I would rather import `krealloc_aligned` and not have this
weird formatting here.

--=20
Cheers,
Benno

> +            if ptr.is_null() {
> +                return Err(AllocError);
> +            }
> +
> +            ptr.cast::<MaybeUninit<T>>()
> +        };
> +
> +        // SAFETY: For non-zero-sized types, we allocate above using the=
 global allocator. For
> +        // zero-sized types, we use `NonNull::dangling`.
> +        Ok(unsafe { Box::from_raw(ptr) })
> +    }
> +}

[...]