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

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Message-ID: <ZrJyaWhXHRciX51o@pollux.localdomain>
Date: Tue, 6 Aug 2024 20:58:49 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
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 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.

> 
> > 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.

This allows us to use our kernel `Box` and `Vec` types in userspace tests
(rusttest target).

> 
> ---
> Cheers,
> Benno
> 
> > +    }
> > +}
> > --
> > 2.45.2
> > 
>