Re: [PATCH v4 05/28] rust: alloc: add module `allocator_test`

[Danilo Krummrich <dakr@kernel.org>]

On Wed, Aug 07, 2024 at 07:20:03AM +0000, Benno Lossin wrote:
> 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@google.com>
> >>> Signed-off-by: Danilo Krummrich <dakr@kernel.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?

I think it's better to have the creation of the allocator_test module and the
implementation of `Cmalloc` in separate patches. `Cmalloc` comes later because I
don't need it yet. I need it to get rid of building Rust's `alloc` crate and I
think it's good to have those patches close to each other.

> 
> ---
> Cheers,
> Benno
>