linux-kernel - Re: [PATCH v9 07/29] rust: alloc: add module `allocator

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Message-ID: <ZwVBliUmvM_1P4a2@cassiopeiae>
Date: Tue, 8 Oct 2024 16:28:38 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
	gary@...yguo.net, bjorn3_gh@...tonmail.com, benno.lossin@...ton.me,
	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,
	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 v9 07/29] rust: alloc: add module `allocator_test`

On Tue, Oct 08, 2024 at 06:10:39AM -0700, Boqun Feng wrote:
> On Fri, Oct 04, 2024 at 05:41:11PM +0200, 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.
> > 
> > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > Reviewed-by: Benno Lossin <benno.lossin@...ton.me>
> > Reviewed-by: Gary Guo <gary@...yguo.net>
> > 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 91b2a26faf3d..f8ddc8d96da9 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,
> 
> The `old_layout` parameter is missing here.

Thanks, good catch.

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index f8ddc8d96da9..28281d600492 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -193,6 +193,7 @@ unsafe fn free(ptr: NonNull<u8>, layout: Layout) {
     }
 }

+#[allow(dead_code)]
 /// Returns a properly aligned dangling pointer from the given `layout`.
 pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> {
     let ptr = layout.align() as *mut u8;
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index 4785efc474a7..c5d325506f0c 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -12,6 +12,7 @@ unsafe impl Allocator for Kmalloc {
     unsafe fn realloc(
         _ptr: Option<NonNull<u8>>,
         _layout: Layout,
+        _old_layout: Layout,
         _flags: Flags,
     ) -> Result<NonNull<[u8]>, AllocError> {
         panic!();

We also have to fix an intermediate dead code warning for `dangling_from_layout`
in the `rusttest` target, until we start using it when we implement `Cmalloc`
in this module.