rust: kernel: remove usage of allocator_api unstable feature

With the adoption of `BoxExt` and `VecExt`, we don't need the functions
provided by this feature (namely the methods prefixed with `try_` and
different allocator per collection instance).

We do need `AllocError`, but we define our own as it is a trivial empty
struct.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20240328013603.206764-11-wedsonaf@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/alloc.rs

@@ -8,6 +8,10 @@
 pub mod box_ext;
 pub mod vec_ext;
 
+/// Indicates an allocation error.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct AllocError;
+
 /// Flags to be used when allocating memory.
 ///
 /// They can be combined with the operators `|`, `&`, and `!`.

rust/kernel/alloc/box_ext.rs

@@ -2,9 +2,8 @@
 
 //! Extensions to [`Box`] for fallible allocations.
 
-use super::Flags;
+use super::{AllocError, Flags};
 use alloc::boxed::Box;
-use core::alloc::AllocError;
 use core::mem::MaybeUninit;
 use core::result::Result;
 

rust/kernel/alloc/vec_ext.rs

@@ -2,8 +2,8 @@
 
 //! Extensions to [`Vec`] for fallible allocations.
 
-use super::Flags;
-use alloc::{alloc::AllocError, vec::Vec};
+use super::{AllocError, Flags};
+use alloc::vec::Vec;
 use core::result::Result;
 
 /// Extensions to [`Vec`].

rust/kernel/error.rs

@@ -4,9 +4,9 @@
 //!
 //! C header: [`include/uapi/asm-generic/errno-base.h`](srctree/include/uapi/asm-generic/errno-base.h)
 
-use crate::str::CStr;
+use crate::{alloc::AllocError, str::CStr};
 
-use alloc::alloc::{AllocError, LayoutError};
+use alloc::alloc::LayoutError;
 
 use core::convert::From;
 use core::fmt;

rust/kernel/init.rs

@@ -211,14 +211,13 @@
 //! [`pin_init!`]: crate::pin_init!
 
 use crate::{
-    alloc::{box_ext::BoxExt, Flags},
+    alloc::{box_ext::BoxExt, AllocError, Flags},
     error::{self, Error},
     sync::UniqueArc,
     types::{Opaque, ScopeGuard},
 };
 use alloc::boxed::Box;
 use core::{
-    alloc::AllocError,
     cell::UnsafeCell,
     convert::Infallible,
     marker::PhantomData,

rust/kernel/lib.rs

@@ -12,7 +12,6 @@
 //! do so first instead of bypassing this crate.
 
 #![no_std]
-#![feature(allocator_api)]
 #![feature(coerce_unsized)]
 #![feature(dispatch_from_dyn)]
 #![feature(new_uninit)]

rust/kernel/str.rs

@@ -2,8 +2,7 @@
 
 //! String representations.
 
-use crate::alloc::{flags::*, vec_ext::VecExt};
-use alloc::alloc::AllocError;
+use crate::alloc::{flags::*, vec_ext::VecExt, AllocError};
 use alloc::vec::Vec;
 use core::fmt::{self, Write};
 use core::ops::{self, Deref, DerefMut, Index};

rust/kernel/sync/arc.rs

@@ -16,7 +16,7 @@
 //! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 
 use crate::{
-    alloc::{box_ext::BoxExt, Flags},
+    alloc::{box_ext::BoxExt, AllocError, Flags},
     bindings,
     error::{self, Error},
     init::{self, InPlaceInit, Init, PinInit},
@@ -25,7 +25,7 @@
 };
 use alloc::boxed::Box;
 use core::{
-    alloc::{AllocError, Layout},
+    alloc::Layout,
     fmt,
     marker::{PhantomData, Unsize},
     mem::{ManuallyDrop, MaybeUninit},

rust/kernel/workqueue.rs

@@ -132,9 +132,8 @@
 //!
 //! C header: [`include/linux/workqueue.h`](srctree/include/linux/workqueue.h)
 
-use crate::alloc::Flags;
+use crate::alloc::{AllocError, Flags};
 use crate::{bindings, prelude::*, sync::Arc, sync::LockClassKey, types::Opaque};
-use alloc::alloc::AllocError;
 use alloc::boxed::Box;
 use core::marker::PhantomData;
 use core::pin::Pin;