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

Benno Lossin
2024-08-07T07:20:07Z

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?

---
Cheers,
Benno