linux-kernel - Re: [PATCH v4 05/28] rust: alloc: add module `allocator

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Message-ID: <6aaf4e2d-7968-4a7c-a522-73e6788ee0ee@proton.me>
Date: Wed, 07 Aug 2024 07:20:03 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...sung.com, aliceryhl@...gle.com, akpm@...ux-foundation.org, daniel.almeida@...labora.com, faith.ekstrand@...labora.com, boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com, zhiw@...dia.com, acurrid@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com, ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 05/28] rust: alloc: add module `allocator_test`

On 06.08.24 20:58, Danilo Krummrich wrote:
> On Tue, Aug 06, 2024 at 04:54:10PM +0000, Benno Lossin wrote:
>> On 05.08.24 17:19, Danilo Krummrich wrote:
>>> `Allocator`s, such as `Kmalloc`, will be used by e.g. `Box` and `Vec` in
>>> subsequent patches, and hence this dependency propagates throughout the
>>> whole kernel.
>>>
>>> Add the `allocator_test` module that provides an empty implementation
>>> for all `Allocator`s in the kernel, such that we don't break the
>>> `rusttest` make target in subsequent patches.
>>
>> This is confusing, since you are talking about both our new `Allocator`
>> trait, allocators and the `alloc` crate `Allocator`.
> 
> I never mention the `alloc` crate `Allocator` here.

Seems like I confused myself...

>>> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>>> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
>>> ---
>>>  rust/kernel/alloc.rs                |  9 +++++++--
>>>  rust/kernel/alloc/allocator_test.rs | 19 +++++++++++++++++++
>>>  2 files changed, 26 insertions(+), 2 deletions(-)
>>>  create mode 100644 rust/kernel/alloc/allocator_test.rs
>>>
>>> diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
>>> index bc01a17df5e0..942e2755f217 100644
>>> --- a/rust/kernel/alloc.rs
>>> +++ b/rust/kernel/alloc.rs
>>> @@ -2,12 +2,17 @@
>>>
>>>  //! Extensions to the [`alloc`] crate.
>>>
>>> -#[cfg(not(test))]
>>> -#[cfg(not(testlib))]
>>> +#[cfg(not(any(test, testlib)))]
>>>  pub mod allocator;
>>>  pub mod box_ext;
>>>  pub mod vec_ext;
>>>
>>> +#[cfg(any(test, testlib))]
>>> +pub mod allocator_test;
>>> +
>>> +#[cfg(any(test, testlib))]
>>> +pub use self::allocator_test as allocator;
>>> +
>>>  /// Indicates an allocation error.
>>>  #[derive(Copy, Clone, PartialEq, Eq, Debug)]
>>>  pub struct AllocError;
>>> diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
>>> new file mode 100644
>>> index 000000000000..4785efc474a7
>>> --- /dev/null
>>> +++ b/rust/kernel/alloc/allocator_test.rs
>>> @@ -0,0 +1,19 @@
>>> +// SPDX-License-Identifier: GPL-2.0
>>> +
>>> +#![allow(missing_docs)]
>>> +
>>> +use super::{AllocError, Allocator, Flags};
>>> +use core::alloc::Layout;
>>> +use core::ptr::NonNull;
>>> +
>>> +pub struct Kmalloc;
>>> +
>>> +unsafe impl Allocator for Kmalloc {
>>> +    unsafe fn realloc(
>>> +        _ptr: Option<NonNull<u8>>,
>>> +        _layout: Layout,
>>> +        _flags: Flags,
>>> +    ) -> Result<NonNull<[u8]>, AllocError> {
>>> +        panic!();
>>
>> Does `build_error!()` also work? If yes, then I would prefer that.
> 
> Probably, but it also probably doesn't matter too much. A later patch in the
> series replaces this with a `Cmalloc` implementation and type aliases all kernel
> allocators (e.g. `Kmalloc`) to it.

What prevents you from doing the `Cmalloc` patch here? `build_error!`
probably doesn't work, since we probably allocate in rusttest, right?

---
Cheers,
Benno