rust: alloc: add module `allocator_test`

`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 <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Signed-off-by: Danilo Krummrich <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Added missing `_old_layout` parameter as discussed. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

1 files changed, 20 insertions, 0 deletions

diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
new file mode 100644
index 000000000000..c5d325506f0c
--- /dev/null
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -0,0 +1,20 @@
+// 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,
+        _old_layout: Layout,
+        _flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        panic!();
+    }
+}