[PATCH v2 00/23] Generic `Allocator` support for Rust

[PATCH v2 00/23] Generic `Allocator` support for Rust

[Danilo Krummrich]

Hi,

This patch series adds generic kernel allocator support for Rust, which so far
is limited to `kmalloc` allocations.

In order to abstain from (re-)adding unstable Rust features to the kernel, this
patch series does not extend the `Allocator` trait from Rust's `alloc` crate,
nor does it extend the `BoxExt` and `VecExt` extensions.

Instead, this series introduces a kernel specific `Allocator` trait, which is
implemented by the `Kmalloc`, `Vmalloc` and `KVmalloc` allocators, also
implemented in the context of this series.

As a consequence we need our own kernel `Box<T, A>` and `Vec<T, A>` types.
Additionally, this series adds the following type aliases:

```
pub type KBox<T> = Box<T, Kmalloc>;
pub type VBox<T> = Box<T, Vmalloc>;
pub type KVBox<T> = Box<T, KVmalloc>;


pub type KVec<T> = Vec<T, Kmalloc>;
pub type VVec<T> = Vec<T, Vmalloc>;
pub type KVVec<T> = Vec<T, KVmalloc>;
```

With that, we can start using the kernel `Box` and `Vec` types throughout the
tree and remove the now obolete extensions `BoxExt` and `VecExt`.

For a final cleanup, this series removes the last minor dependencies to Rust's
`alloc` crate and removes it from the entire kernel build.

The series ensures not to break the `rusttest` make target by implementing the
`allocator_test` module providing a stub implementation for all kernel
`Allocator`s.

This patch series passes all KUnit tests, including the ones added by this
series. Additionally, the tests were run with `kmemleak` and `KASAN` enabled,
without any issues.

This series is based in [1], which just hit -mm/mm-unstable, and is also
available in [2].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=mm/krealloc
[2] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/mm

Changes in v2:
  - preserve `impl GlobalAlloc for Kmalloc` and remove it at the end (Benno)
  - remove `&self` parameter from all `Allocator` functions (Benno)
  - various documentation fixes for `Allocator` (Benno)
  - use `NonNull<u8>` for `Allocator::free` and `Option<NonNull<u8>>` for
    `Allocator::realloc` (Benno)
  - fix leak of `IntoIter` in `Vec::collect` (Boqun)
  - always realloc (try to shrink) in `Vec::collect`, it's up the the
    `Allocator` to provide a heuristic whether it makes sense to actually shrink
  - rename `KBox<T, A>` -> `Box<T, A>` and `KVec<T, A>` -> `Vec<T, A>` and
    provide type aliases `KBox<T>`, `VBox<T>`, `KVBox<T>`, etc.
    - This allows for much cleaner code and, in combination with removing
      `&self` parameters from `Allocator`s, gets us rid of the need for
      `Box::new` and `Box::new_alloc` and all other "_alloc" postfixed
      functions.
    - Before: `KBox::new_alloc(foo, Vmalloc)?`
    - After:  `VBox::new(foo)?`, which resolves to
              `Box::<Foo,  Vmalloc>::new(foo)?;

Danilo Krummrich (23):
  rust: alloc: add `Allocator` trait
  rust: alloc: separate `aligned_size` from `krealloc_aligned`
  rust: alloc: rename `KernelAllocator` to `Kmalloc`
  rust: alloc: implement `Allocator` for `Kmalloc`
  rust: alloc: add module `allocator_test`
  rust: alloc: implement `Vmalloc` allocator
  rust: alloc: implement `KVmalloc` allocator
  rust: types: implement `Unique<T>`
  rust: alloc: implement kernel `Box`
  rust: treewide: switch to our kernel `Box` type
  rust: alloc: remove `BoxExt` extension
  rust: alloc: add `Box` to prelude
  rust: alloc: import kernel `Box` type in types.rs
  rust: alloc: implement kernel `Vec` type
  rust: alloc: implement `IntoIterator` for `Vec`
  rust: alloc: implement `collect` for `IntoIter`
  rust: treewide: switch to the kernel `Vec` type
  rust: alloc: remove `VecExt` extension
  rust: alloc: add `Vec` to prelude
  rust: alloc: remove `GlobalAlloc` and `krealloc_aligned`
  rust: error: use `core::alloc::LayoutError`
  rust: str: test: replace `alloc::format`
  kbuild: rust: remove the `alloc` crate

 rust/Makefile                       |  44 +-
 rust/exports.c                      |   1 -
 rust/helpers.c                      |  15 +
 rust/kernel/alloc.rs                |  99 +++-
 rust/kernel/alloc/allocator.rs      | 147 +++--
 rust/kernel/alloc/allocator_test.rs |  23 +
 rust/kernel/alloc/box_ext.rs        |  56 --
 rust/kernel/alloc/kbox.rs           | 344 ++++++++++++
 rust/kernel/alloc/kvec.rs           | 831 ++++++++++++++++++++++++++++
 rust/kernel/alloc/vec_ext.rs        | 185 -------
 rust/kernel/error.rs                |   2 +-
 rust/kernel/init.rs                 |  49 +-
 rust/kernel/init/__internal.rs      |   2 +-
 rust/kernel/lib.rs                  |   1 -
 rust/kernel/prelude.rs              |   5 +-
 rust/kernel/str.rs                  |  78 ++-
 rust/kernel/sync/arc.rs             |  17 +-
 rust/kernel/sync/condvar.rs         |   4 +-
 rust/kernel/sync/lock/mutex.rs      |   2 +-
 rust/kernel/sync/lock/spinlock.rs   |   2 +-
 rust/kernel/sync/locked_by.rs       |   2 +-
 rust/kernel/types.rs                | 192 ++++++-
 rust/kernel/workqueue.rs            |  20 +-
 samples/rust/rust_minimal.rs        |   4 +-
 scripts/Makefile.build              |   7 +-
 25 files changed, 1713 insertions(+), 419 deletions(-)
 create mode 100644 rust/kernel/alloc/allocator_test.rs
 delete mode 100644 rust/kernel/alloc/box_ext.rs
 create mode 100644 rust/kernel/alloc/kbox.rs
 create mode 100644 rust/kernel/alloc/kvec.rs
 delete mode 100644 rust/kernel/alloc/vec_ext.rs


base-commit: d270beaca6818349b2aed7e6034b800a777087cc
-- 
2.45.2

[PATCH v2 01/23] rust: alloc: add `Allocator` trait

[Danilo Krummrich]

Add a kernel specific `Allocator` trait, that in contrast to the one in
Rust's core library doesn't require unstable features and supports GFP
flags.

Subsequent patches add the following trait implementors: `Kmalloc`,
`Vmalloc` and `KVmalloc`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs | 73 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 531b5e471cb1..11d12264c194 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -11,6 +11,7 @@
 /// Indicates an allocation error.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct AllocError;
+use core::{alloc::Layout, ptr::NonNull};
 
 /// Flags to be used when allocating memory.
 ///
@@ -71,3 +72,75 @@ pub mod flags {
     /// small allocations.
     pub const GFP_NOWAIT: Flags = Flags(bindings::GFP_NOWAIT);
 }
+
+/// The kernel's [`Allocator`] trait.
+///
+/// An implementation of [`Allocator`] can allocate, re-allocate and free memory buffer described
+/// via [`Layout`].
+///
+/// [`Allocator`] is designed to be implemented as a ZST; [`Allocator`] functions do not operate on
+/// an object instance.
+///
+/// # Safety
+///
+/// Memory returned from an allocator must point to a valid memory buffer and remain valid until
+/// it is explicitly freed.
+///
+/// Any pointer to a memory buffer which is currently allocated must be valid to be passed to any
+/// other [`Allocator`] function. The same applies for a NULL pointer.
+///
+/// If `realloc` is called with:
+///   - a size of zero, the given memory allocation, if any, must be freed
+///   - a NULL pointer, a new memory allocation must be created
+pub unsafe trait Allocator {
+    /// Allocate memory based on `layout` and `flags`.
+    ///
+    /// On success, returns a buffer represented as `NonNull<[u8]>` that satisfies the layout
+    /// constraints (i.e. minimum size and alignment as specified by `layout`).
+    ///
+    /// This function is equivalent to `realloc` when called with a NULL pointer.
+    fn alloc(layout: Layout, flags: Flags) -> Result<NonNull<[u8]>, AllocError> {
+        // SAFETY: Passing a NULL pointer to `realloc` is valid by it's safety requirements and asks
+        // for a new memory allocation.
+        unsafe { Self::realloc(None, layout, flags) }
+    }
+
+    /// Re-allocate an existing memory allocation to satisfy the requested `layout`. If the
+    /// requested size is zero, `realloc` behaves equivalent to `free`.
+    ///
+    /// If the requested size is larger than the size of the existing allocation, a successful call
+    /// to `realloc` guarantees that the new or grown buffer has at least `Layout::size` bytes, but
+    /// may also be larger.
+    ///
+    /// If the requested size is smaller than the size of the existing allocation, `realloc` may or
+    /// may not shrink the buffer; this is implementation specific to the allocator.
+    ///
+    /// On allocation failure, the existing buffer, if any, remains valid.
+    ///
+    /// The buffer is represented as `NonNull<[u8]>`.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must point to an existing and valid memory allocation created by this allocator
+    /// instance.
+    ///
+    /// Additionally, `ptr` is allowed to be a NULL pointer; in this case a new memory allocation is
+    /// created.
+    unsafe fn realloc(
+        ptr: Option<NonNull<u8>>,
+        layout: Layout,
+        flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError>;
+
+    /// Free an existing memory allocation.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must point to an existing and valid memory allocation created by this `Allocator`
+    /// instance.
+    unsafe fn free(ptr: NonNull<u8>) {
+        // SAFETY: `ptr` is guaranteed to be previously allocated with this `Allocator` or NULL.
+        // Calling `realloc` with a buffer size of zero, frees the buffer `ptr` points to.
+        let _ = unsafe { Self::realloc(Some(ptr), Layout::new::<()>(), Flags(0)) };
+    }
+}
-- 
2.45.2

[PATCH v2 02/23] rust: alloc: separate `aligned_size` from `krealloc_aligned`

[Danilo Krummrich]

Separate `aligned_size` from `krealloc_aligned`.

Subsequent patches implement `Allocator` derivates, such as `Kmalloc`,
that require `aligned_size` and replace the original `krealloc_aligned`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/allocator.rs | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e6ea601f38c6..6e133780a4a1 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -8,27 +8,35 @@
 
 struct KernelAllocator;
 
-/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
-///
-/// # Safety
-///
-/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
-/// - `new_layout` must have a non-zero size.
-pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
+fn aligned_size(new_layout: Layout) -> usize {
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
     let layout = new_layout.pad_to_align();
 
     // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
     // which together with the slab guarantees means the `krealloc` will return a properly aligned
     // object (see comments in `kmalloc()` for more information).
-    let size = layout.size();
+    layout.size()
+}
 
+/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
+///
+/// # Safety
+///
+/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
+/// - `new_layout` must have a non-zero size.
+pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
     // SAFETY:
     // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
     //   function safety requirement.
     // - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
     //   to the function safety requirement)
-    unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
+    unsafe {
+        bindings::krealloc(
+            ptr as *const core::ffi::c_void,
+            aligned_size(new_layout),
+            flags.0,
+        ) as *mut u8
+    }
 }
 
 unsafe impl GlobalAlloc for KernelAllocator {
-- 
2.45.2

[PATCH v2 03/23] rust: alloc: rename `KernelAllocator` to `Kmalloc`

[Danilo Krummrich]

Subsequent patches implement `Vmalloc` and `KVmalloc` allocators, hence
align `KernelAllocator` to this naming scheme.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/allocator.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 6e133780a4a1..10774c51ae26 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -6,7 +6,7 @@
 use core::alloc::{GlobalAlloc, Layout};
 use core::ptr;
 
-struct KernelAllocator;
+struct Kmalloc;
 
 fn aligned_size(new_layout: Layout) -> usize {
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
@@ -39,7 +39,7 @@ pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: F
     }
 }
 
-unsafe impl GlobalAlloc for KernelAllocator {
+unsafe impl GlobalAlloc for Kmalloc {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
         // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
         // requirement.
@@ -75,7 +75,7 @@ unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
 }
 
 #[global_allocator]
-static ALLOCATOR: KernelAllocator = KernelAllocator;
+static ALLOCATOR: Kmalloc = Kmalloc;
 
 // See <https://github.com/rust-lang/rust/pull/86844>.
 #[no_mangle]
-- 
2.45.2

[PATCH v2 04/23] rust: alloc: implement `Allocator` for `Kmalloc`

[Danilo Krummrich]

Implement `Allocator` for `Kmalloc`, the kernel's default allocator,
typically used for objects smaller than page size.

All memory allocations made with `Kmalloc` end up in `krealloc()`.

It serves as allocator for the subsequently introduced types `KBox` and
`KVec`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs           |  2 +-
 rust/kernel/alloc/allocator.rs | 66 ++++++++++++++++++++++++++++++++--
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 11d12264c194..bf739ce65387 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -4,7 +4,7 @@
 
 #[cfg(not(test))]
 #[cfg(not(testlib))]
-mod allocator;
+pub mod allocator;
 pub mod box_ext;
 pub mod vec_ext;
 
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 10774c51ae26..397ae5bcc043 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -5,9 +5,18 @@
 use super::{flags::*, Flags};
 use core::alloc::{GlobalAlloc, Layout};
 use core::ptr;
+use core::ptr::NonNull;
 
-struct Kmalloc;
+use crate::alloc::{AllocError, Allocator};
+use crate::bindings;
 
+/// The contiguous kernel allocator.
+///
+/// The contiguous kernel allocator only ever allocates physically contiguous memory through
+/// `bindings::krealloc`.
+pub struct Kmalloc;
+
+/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
 fn aligned_size(new_layout: Layout) -> usize {
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
     let layout = new_layout.pad_to_align();
@@ -18,7 +27,7 @@ fn aligned_size(new_layout: Layout) -> usize {
     layout.size()
 }
 
-/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
+/// Calls `krealloc` with a proper size to alloc a new object.
 ///
 /// # Safety
 ///
@@ -39,6 +48,59 @@ pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: F
     }
 }
 
+struct ReallocFunc(
+    // INVARIANT: One of the following `krealloc`, `vrealloc`, `kvrealloc`.
+    unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void,
+);
+
+impl ReallocFunc {
+    fn krealloc() -> Self {
+        Self(bindings::krealloc)
+    }
+
+    // SAFETY: `call` has the exact same safety requirements as `Allocator::realloc`.
+    unsafe fn call(
+        &self,
+        ptr: Option<NonNull<u8>>,
+        layout: Layout,
+        flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        let size = aligned_size(layout);
+        let ptr = match ptr {
+            Some(ptr) => ptr.as_ptr(),
+            None => ptr::null(),
+        };
+
+        // SAFETY: `ptr` is valid by the safety requirements of this function.
+        let raw_ptr = unsafe {
+            // If `size == 0` and `ptr != NULL` the memory behind the pointer is freed.
+            self.0(ptr.cast(), size, flags.0).cast()
+        };
+
+        let ptr = if size == 0 {
+            NonNull::dangling()
+        } else {
+            NonNull::new(raw_ptr).ok_or(AllocError)?
+        };
+
+        Ok(NonNull::slice_from_raw_parts(ptr, size))
+    }
+}
+
+unsafe impl Allocator for Kmalloc {
+    unsafe fn realloc(
+        ptr: Option<NonNull<u8>>,
+        layout: Layout,
+        flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        let realloc = ReallocFunc::krealloc();
+
+        // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
+        // allocated with this `Allocator`.
+        unsafe { realloc.call(ptr, layout, flags) }
+    }
+}
+
 unsafe impl GlobalAlloc for Kmalloc {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
         // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
-- 
2.45.2

[PATCH v2 05/23] rust: alloc: add module `allocator_test`

[Danilo Krummrich]

`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.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs                |  9 +++++++--
 rust/kernel/alloc/allocator_test.rs | 21 +++++++++++++++++++++
 2 files changed, 28 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 bf739ce65387..90ebe79e86cb 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..3a0abe65491d
--- /dev/null
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -0,0 +1,21 @@
+// 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(
+        &self,
+        _old_ptr: *mut u8,
+        _old_size: usize,
+        _layout: Layout,
+        _flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        panic!();
+    }
+}
-- 
2.45.2

[PATCH v2 06/23] rust: alloc: implement `Vmalloc` allocator

[Danilo Krummrich]

Implement `Allocator` for `Vmalloc`, the kernel's virtually contiguous
allocator, typically used for larger objects, (much) larger than page
size.

All memory allocations made with `Vmalloc` end up in `vrealloc()`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/helpers.c                      |  8 ++++++++
 rust/kernel/alloc/allocator.rs      | 24 ++++++++++++++++++++++++
 rust/kernel/alloc/allocator_test.rs |  1 +
 3 files changed, 33 insertions(+)

diff --git a/rust/helpers.c b/rust/helpers.c
index 3df5217fb2ff..5ca7e4872ee8 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -30,6 +30,7 @@
 #include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
+#include <linux/vmalloc.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 
@@ -165,6 +166,13 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
 }
 EXPORT_SYMBOL_GPL(rust_helper_krealloc);
 
+void * __must_check __realloc_size(2)
+rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
+{
+	return vrealloc(p, size, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_vrealloc);
+
 /*
  * `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
  * use it in contexts where Rust expects a `usize` like slice (array) indices.
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 397ae5bcc043..e9a3d0694f41 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -16,6 +16,12 @@
 /// `bindings::krealloc`.
 pub struct Kmalloc;
 
+/// The virtually contiguous kernel allocator.
+///
+/// The vmalloc allocator allocates pages from the page level allocator and maps them into the
+/// contiguous kernel virtual space.
+pub struct Vmalloc;
+
 /// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
 fn aligned_size(new_layout: Layout) -> usize {
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
@@ -58,6 +64,10 @@ fn krealloc() -> Self {
         Self(bindings::krealloc)
     }
 
+    fn vrealloc() -> Self {
+        Self(bindings::vrealloc)
+    }
+
     // SAFETY: `call` has the exact same safety requirements as `Allocator::realloc`.
     unsafe fn call(
         &self,
@@ -136,6 +146,20 @@ unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
     }
 }
 
+unsafe impl Allocator for Vmalloc {
+    unsafe fn realloc(
+        ptr: Option<NonNull<u8>>,
+        layout: Layout,
+        flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        let realloc = ReallocFunc::vrealloc();
+
+        // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
+        // allocated with this `Allocator`.
+        unsafe { realloc.call(ptr, layout, flags) }
+    }
+}
+
 #[global_allocator]
 static ALLOCATOR: Kmalloc = Kmalloc;
 
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index 3a0abe65491d..b2d7db492ba6 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -7,6 +7,7 @@
 use core::ptr::NonNull;
 
 pub struct Kmalloc;
+pub type Vmalloc = Kmalloc;
 
 unsafe impl Allocator for Kmalloc {
     unsafe fn realloc(
-- 
2.45.2

[PATCH v2 07/23] rust: alloc: implement `KVmalloc` allocator

[Danilo Krummrich]

Implement `Allocator` for `KVmalloc`, an `Allocator` that tries to
allocate memory wth `kmalloc` first and, on failure, falls back to
`vmalloc`.

All memory allocations made with `KVmalloc` end up in
`kvrealloc_noprof()`; all frees in `kvfree()`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/helpers.c                      |  7 +++++++
 rust/kernel/alloc/allocator.rs      | 24 ++++++++++++++++++++++++
 rust/kernel/alloc/allocator_test.rs |  1 +
 3 files changed, 32 insertions(+)

diff --git a/rust/helpers.c b/rust/helpers.c
index 5ca7e4872ee8..19a5e4a0c7ee 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -173,6 +173,13 @@ rust_helper_vrealloc(const void *p, size_t size, gfp_t flags)
 }
 EXPORT_SYMBOL_GPL(rust_helper_vrealloc);
 
+void * __must_check __realloc_size(2)
+rust_helper_kvrealloc(const void *p, size_t size, gfp_t flags)
+{
+	return kvrealloc(p, size, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_kvrealloc);
+
 /*
  * `bindgen` binds the C `size_t` type as the Rust `usize` type, so we can
  * use it in contexts where Rust expects a `usize` like slice (array) indices.
diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index e9a3d0694f41..1e53f149db96 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -22,6 +22,12 @@
 /// contiguous kernel virtual space.
 pub struct Vmalloc;
 
+/// The kvmalloc kernel allocator.
+///
+/// Attempt to allocate physically contiguous memory, but upon failure, fall back to non-contiguous
+/// (vmalloc) allocation.
+pub struct KVmalloc;
+
 /// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
 fn aligned_size(new_layout: Layout) -> usize {
     // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
@@ -68,6 +74,10 @@ fn vrealloc() -> Self {
         Self(bindings::vrealloc)
     }
 
+    fn kvrealloc() -> Self {
+        Self(bindings::kvrealloc)
+    }
+
     // SAFETY: `call` has the exact same safety requirements as `Allocator::realloc`.
     unsafe fn call(
         &self,
@@ -160,6 +170,20 @@ unsafe fn realloc(
     }
 }
 
+unsafe impl Allocator for KVmalloc {
+    unsafe fn realloc(
+        ptr: Option<NonNull<u8>>,
+        layout: Layout,
+        flags: Flags,
+    ) -> Result<NonNull<[u8]>, AllocError> {
+        let realloc = ReallocFunc::kvrealloc();
+
+        // SAFETY: If not `None`, `ptr` is guaranteed to point to valid memory, which was previously
+        // allocated with this `Allocator`.
+        unsafe { realloc.call(ptr, layout, flags) }
+    }
+}
+
 #[global_allocator]
 static ALLOCATOR: Kmalloc = Kmalloc;
 
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index b2d7db492ba6..f0e96016b196 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -8,6 +8,7 @@
 
 pub struct Kmalloc;
 pub type Vmalloc = Kmalloc;
+pub type KVmalloc = Kmalloc;
 
 unsafe impl Allocator for Kmalloc {
     unsafe fn realloc(
-- 
2.45.2

[PATCH v2 08/23] rust: types: implement `Unique<T>`

[Danilo Krummrich]

Implement the `Unique` type as a prerequisite for `Box` and `Vec`
introduced in subsequent patches.

`Unique` serves as wrapper around a `NonNull`, but indicates that the
possessor of this wrapper owns the referent.

This type already exists in Rust's core library, but, unfortunately, is
exposed as unstable API and hence shouldn't be used in the kernel.

This implementation of `Unique` is almost identical, but mostly stripped
down to the functionality we need for `Box` and `Vec`. Additionally, all
unstable features are removed and / or replaced by stable ones.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/types.rs | 183 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 183 insertions(+)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 2e7c9008621f..9cd20fe41c20 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -409,3 +409,186 @@ pub enum Either<L, R> {
     /// Constructs an instance of [`Either`] containing a value of type `R`.
     Right(R),
 }
+
+/// A wrapper around a raw non-null `*mut T` that indicates that the possessor
+/// of this wrapper owns the referent. Useful for building abstractions like
+/// `Box<T>`, `Vec<T>`, `String`, and `HashMap<K, V>`.
+///
+/// Unlike `*mut T`, `Unique<T>` behaves "as if" it were an instance of `T`.
+/// It implements `Send`/`Sync` if `T` is `Send`/`Sync`. It also implies
+/// the kind of strong aliasing guarantees an instance of `T` can expect:
+/// the referent of the pointer should not be modified without a unique path to
+/// its owning Unique.
+///
+/// If you're uncertain of whether it's correct to use `Unique` for your purposes,
+/// consider using `NonNull`, which has weaker semantics.
+///
+/// Unlike `*mut T`, the pointer must always be non-null, even if the pointer
+/// is never dereferenced. This is so that enums may use this forbidden value
+/// as a discriminant -- `Option<Unique<T>>` has the same size as `Unique<T>`.
+/// However the pointer may still dangle if it isn't dereferenced.
+///
+/// Unlike `*mut T`, `Unique<T>` is covariant over `T`. This should always be correct
+/// for any type which upholds Unique's aliasing requirements.
+#[repr(transparent)]
+pub struct Unique<T: ?Sized> {
+    pointer: NonNull<T>,
+    // NOTE: this marker has no consequences for variance, but is necessary
+    // for dropck to understand that we logically own a `T`.
+    //
+    // For details, see:
+    // https://github.com/rust-lang/rfcs/blob/master/text/0769-sound-generic-drop.md#phantom-data
+    _marker: PhantomData<T>,
+}
+
+/// `Unique` pointers are `Send` if `T` is `Send` because the data they
+/// reference is unaliased. Note that this aliasing invariant is
+/// unenforced by the type system; the abstraction using the
+/// `Unique` must enforce it.
+unsafe impl<T: Send + ?Sized> Send for Unique<T> {}
+
+/// `Unique` pointers are `Sync` if `T` is `Sync` because the data they
+/// reference is unaliased. Note that this aliasing invariant is
+/// unenforced by the type system; the abstraction using the
+/// `Unique` must enforce it.
+unsafe impl<T: Sync + ?Sized> Sync for Unique<T> {}
+
+impl<T: Sized> Unique<T> {
+    /// Creates a new `Unique` that is dangling, but well-aligned.
+    ///
+    /// This is useful for initializing types which lazily allocate, like
+    /// `Vec::new` does.
+    ///
+    /// Note that the pointer value may potentially represent a valid pointer to
+    /// a `T`, which means this must not be used as a "not yet initialized"
+    /// sentinel value. Types that lazily allocate must track initialization by
+    /// some other means.
+    #[must_use]
+    #[inline]
+    pub const fn dangling() -> Self {
+        Unique {
+            pointer: NonNull::dangling(),
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T: ?Sized> Unique<T> {
+    /// Creates a new `Unique`.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be non-null.
+    #[inline]
+    pub const unsafe fn new_unchecked(ptr: *mut T) -> Self {
+        // SAFETY: the caller must guarantee that `ptr` is non-null.
+        unsafe {
+            Unique {
+                pointer: NonNull::new_unchecked(ptr),
+                _marker: PhantomData,
+            }
+        }
+    }
+
+    /// Creates a new `Unique` if `ptr` is non-null.
+    #[allow(clippy::manual_map)]
+    #[inline]
+    pub fn new(ptr: *mut T) -> Option<Self> {
+        if let Some(pointer) = NonNull::new(ptr) {
+            Some(Unique {
+                pointer,
+                _marker: PhantomData,
+            })
+        } else {
+            None
+        }
+    }
+
+    /// Acquires the underlying `*mut` pointer.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[inline]
+    pub const fn as_ptr(self) -> *mut T {
+        self.pointer.as_ptr()
+    }
+
+    /// Dereferences the content.
+    ///
+    /// The resulting lifetime is bound to self so this behaves "as if"
+    /// it were actually an instance of T that is getting borrowed. If a longer
+    /// (unbound) lifetime is needed, use `&*my_ptr.as_ptr()`.
+    ///
+    /// # Safety
+    ///
+    /// Safety requirements for this function are inherited from [NonNull::as_ref].
+    ///
+    #[must_use]
+    #[inline]
+    pub const unsafe fn as_ref(&self) -> &T {
+        // SAFETY: the caller must guarantee that `self` meets all the
+        // requirements for a reference.
+        unsafe { self.pointer.as_ref() }
+    }
+
+    /// Mutably dereferences the content.
+    ///
+    /// The resulting lifetime is bound to self so this behaves "as if"
+    /// it were actually an instance of T that is getting borrowed. If a longer
+    /// (unbound) lifetime is needed, use `&mut *my_ptr.as_ptr()`.
+    ///
+    /// # Safety
+    ///
+    /// Safety requirements for this function are inherited from [NonNull::as_mut].
+    #[must_use]
+    #[inline]
+    pub unsafe fn as_mut(&mut self) -> &mut T {
+        // SAFETY: the caller must guarantee that `self` meets all the
+        // requirements for a mutable reference.
+        unsafe { self.pointer.as_mut() }
+    }
+
+    /// Casts to a pointer of another type.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[inline]
+    pub fn cast<U>(self) -> Unique<U> {
+        Unique::from(self.pointer.cast())
+    }
+
+    /// Acquires the underlying `*mut` pointer.
+    #[must_use = "`self` will be dropped if the result is not used"]
+    #[inline]
+    pub const fn as_non_null(self) -> NonNull<T> {
+        self.pointer
+    }
+}
+
+impl<T: ?Sized> Clone for Unique<T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized> Copy for Unique<T> {}
+
+impl<T: ?Sized> From<&mut T> for Unique<T> {
+    /// Converts a `&mut T` to a `Unique<T>`.
+    ///
+    /// This conversion is infallible since references cannot be null.
+    #[inline]
+    fn from(reference: &mut T) -> Self {
+        Self::from(NonNull::from(reference))
+    }
+}
+
+impl<T: ?Sized> From<NonNull<T>> for Unique<T> {
+    /// Converts a `NonNull<T>` to a `Unique<T>`.
+    ///
+    /// This conversion is infallible since `NonNull` cannot be null.
+    #[inline]
+    fn from(pointer: NonNull<T>) -> Self {
+        Unique {
+            pointer,
+            _marker: PhantomData,
+        }
+    }
+}
-- 
2.45.2

[PATCH v2 09/23] rust: alloc: implement kernel `Box`

[Danilo Krummrich]

`Box` provides the simplest way to allocate memory for a generic type
with one of the kernel's allocators, e.g. `Kmalloc`, `Vmalloc` or
`KVmalloc`.

In contrast to Rust's `Box` type, the kernel `Box` type considers the
kernel's GFP flags for all appropriate functions, always reports
allocation failures through `Result<_, AllocError>` and remains
independent from unstable features.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs      |   6 +
 rust/kernel/alloc/kbox.rs | 330 ++++++++++++++++++++++++++++++++++++++
 rust/kernel/init.rs       |  32 +++-
 rust/kernel/prelude.rs    |   2 +-
 rust/kernel/types.rs      |  26 +++
 5 files changed, 394 insertions(+), 2 deletions(-)
 create mode 100644 rust/kernel/alloc/kbox.rs

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 90ebe79e86cb..d9809368643e 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -5,6 +5,7 @@
 #[cfg(not(any(test, testlib)))]
 pub mod allocator;
 pub mod box_ext;
+pub mod kbox;
 pub mod vec_ext;
 
 #[cfg(any(test, testlib))]
@@ -13,6 +14,11 @@
 #[cfg(any(test, testlib))]
 pub use self::allocator_test as allocator;
 
+pub use self::kbox::Box;
+pub use self::kbox::KBox;
+pub use self::kbox::KVBox;
+pub use self::kbox::VBox;
+
 /// Indicates an allocation error.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct AllocError;
diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
new file mode 100644
index 000000000000..eb4a5ff500b8
--- /dev/null
+++ b/rust/kernel/alloc/kbox.rs
@@ -0,0 +1,330 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Implementation of [`Box`].
+
+use super::{AllocError, Allocator, Flags};
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::mem::MaybeUninit;
+use core::ops::{Deref, DerefMut};
+use core::pin::Pin;
+use core::ptr;
+use core::result::Result;
+
+use crate::types::Unique;
+
+/// The kernel's `Box` type named [`Box`].
+///
+/// `Box` provides the simplest way to allocate memory for a generic type with one of the kernel's
+/// allocators, e.g. `Kmalloc`, `Vmalloc` or `KVmalloc`.
+///
+/// For non-zero-sized values, a [`Box`] will use the given allocator `A` for its allocation. For
+/// the most common allocators the type aliases `KBox`, `VBox` and `KVBox` exist.
+///
+/// It is valid to convert both ways between a [`Box`] and a raw pointer allocated with any
+/// `Allocator`, given that the `Layout` used with the allocator is correct for the type.
+///
+/// For zero-sized values the [`Box`]' pointer must be `dangling_mut::<T>`; no memory is allocated.
+///
+/// So long as `T: Sized`, a `Box<T>` is guaranteed to be represented as a single pointer and is
+/// also ABI-compatible with C pointers (i.e. the C type `T*`).
+///
+/// # Invariants
+///
+/// The [`Box`]' pointer always properly aligned and either points to memory allocated with `A` or,
+/// for zero-sized types, is a dangling pointer.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::alloc::allocator::Kmalloc;
+///
+/// let b = KBox::<u64>::new(24_u64, GFP_KERNEL)?;
+///
+/// assert_eq!(*b, 24_u64);
+///
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// ```
+/// use kernel::alloc::allocator::KVmalloc;
+///
+/// struct Huge([u8; 1 << 24]);
+///
+/// assert!(KVBox::<Huge>::new_uninit(GFP_KERNEL).is_ok());
+/// ```
+pub struct Box<T: ?Sized, A: Allocator>(Unique<T>, PhantomData<A>);
+
+/// Type alias for `Box` with a `Kmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let b = KBox::new(24_u64, GFP_KERNEL)?;
+///
+/// assert_eq!(*b, 24_u64);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type KBox<T> = Box<T, super::allocator::Kmalloc>;
+
+/// Type alias for `Box` with a `Vmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let b = VBox::new(24_u64, GFP_KERNEL)?;
+///
+/// assert_eq!(*b, 24_u64);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type VBox<T> = Box<T, super::allocator::Vmalloc>;
+
+/// Type alias for `Box` with a `KVmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let b = KVBox::new(24_u64, GFP_KERNEL)?;
+///
+/// assert_eq!(*b, 24_u64);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type KVBox<T> = Box<T, super::allocator::KVmalloc>;
+
+impl<T, A> Box<T, A>
+where
+    T: ?Sized,
+    A: Allocator,
+{
+    /// Constructs a `Box<T, A>` from a raw pointer.
+    ///
+    /// # Safety
+    ///
+    /// `raw` must point to valid memory, previously allocated with `A`, and at least the size of
+    /// type `T`.
+    #[inline]
+    pub const unsafe fn from_raw_alloc(raw: *mut T, alloc: PhantomData<A>) -> Self {
+        // SAFETY: Safe by the requirements of this function.
+        Box(unsafe { Unique::new_unchecked(raw) }, alloc)
+    }
+
+    /// Consumes the `Box<T, A>`, returning a wrapped raw pointer and the allocator it was
+    /// allocated with.
+    pub fn into_raw_alloc(self) -> (*mut T, PhantomData<A>) {
+        let b = ManuallyDrop::new(self);
+        let alloc = unsafe { ptr::read(&b.1) };
+        (b.0.as_ptr(), alloc)
+    }
+
+    /// Constructs a `Box<T, A>` from a raw pointer.
+    ///
+    /// # Safety
+    ///
+    /// `raw` must point to valid memory, previously allocated with `A`, and at least the size of
+    /// type `T`.
+    #[inline]
+    pub const unsafe fn from_raw(raw: *mut T) -> Self {
+        // SAFETY: Validity of `raw` is guaranteed by the safety preconditions of this function.
+        unsafe { Box::from_raw_alloc(raw, PhantomData::<A>) }
+    }
+
+    /// Consumes the `Box<T>`, returning a wrapped raw pointer.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let x = KBox::new(24, GFP_KERNEL)?;
+    /// let ptr = KBox::into_raw(x);
+    /// let x = unsafe { KBox::from_raw(ptr) };
+    ///
+    /// assert_eq!(*x, 24);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    #[inline]
+    pub fn into_raw(self) -> *mut T {
+        self.into_raw_alloc().0
+    }
+
+    /// Consumes and leaks the `Box<T>`, returning a mutable reference, &'a mut T.
+    #[inline]
+    pub fn leak<'a>(b: Self) -> &'a mut T
+    where
+        T: 'a,
+    {
+        // SAFETY: `Box::into_raw` always returns a properly aligned and dereferenceable pointer
+        // which points to an initialized instance of `T`.
+        unsafe { &mut *Box::into_raw(b) }
+    }
+
+    /// Converts a `Box<T>` into a `Pin<Box<T>>`.
+    #[inline]
+    pub fn into_pin(b: Self) -> Pin<Self>
+    where
+        A: 'static,
+    {
+        // SAFETY: It's not possible to move or replace the insides of a `Pin<Box<T>>` when
+        // `T: !Unpin`, so it's safe to pin it directly without any additional requirements.
+        unsafe { Pin::new_unchecked(b) }
+    }
+}
+
+impl<T, A> Box<MaybeUninit<T>, A>
+where
+    A: Allocator,
+{
+    /// Converts to `Box<T, A>`.
+    ///
+    /// # Safety
+    ///
+    /// As with MaybeUninit::assume_init, it is up to the caller to guarantee that the value really
+    /// is in an initialized state. Calling this when the content is not yet fully initialized
+    /// causes immediate undefined behavior.
+    pub unsafe fn assume_init(self) -> Box<T, A> {
+        let raw = Box::into_raw(self);
+        // SAFETY: Reconstruct the `Box<MaybeUninit<T>, A>` as Box<T, A> now that has been
+        // initialized. `raw` and `alloc` are safe by the invariants of `Box`.
+        unsafe { Box::from_raw(raw as *mut T) }
+    }
+
+    /// Writes the value and converts to `Box<T, A>`.
+    pub fn write(mut boxed: Self, value: T) -> Box<T, A> {
+        (*boxed).write(value);
+        // SAFETY: We've just initialized `boxed`'s value.
+        unsafe { boxed.assume_init() }
+    }
+}
+
+impl<T, A> Box<T, A>
+where
+    A: Allocator,
+{
+    fn is_zst() -> bool {
+        core::mem::size_of::<T>() == 0
+    }
+
+    /// Allocates memory with the allocator `A` and then places `x` into it.
+    ///
+    /// This doesn’t actually allocate if T is zero-sized.
+    pub fn new(x: T, flags: Flags) -> Result<Self, AllocError> {
+        let b = Self::new_uninit(flags)?;
+        Ok(Box::write(b, x))
+    }
+
+    /// Constructs a new `Box<T, A>` with uninitialized contents.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let b = KBox::<u64>::new_uninit(GFP_KERNEL)?;
+    /// let b = KBox::write(b, 24);
+    ///
+    /// assert_eq!(*b, 24_u64);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>, A>, AllocError> {
+        let ptr = if Self::is_zst() {
+            Unique::dangling()
+        } else {
+            let layout = core::alloc::Layout::new::<MaybeUninit<T>>();
+            let ptr = A::alloc(layout, flags)?;
+
+            ptr.cast().into()
+        };
+
+        Ok(Box(ptr, PhantomData::<A>))
+    }
+
+    /// Constructs a new `Pin<Box<T, A>>`. If `T` does not implement [`Unpin`], then `x` will be
+    /// pinned in memory and unable to be moved.
+    #[inline]
+    pub fn pin(x: T, flags: Flags) -> Result<Pin<Box<T, A>>, AllocError>
+    where
+        A: 'static,
+    {
+        Ok(Self::new(x, flags)?.into())
+    }
+}
+
+impl<T, A> From<Box<T, A>> for Pin<Box<T, A>>
+where
+    T: ?Sized,
+    A: Allocator,
+    A: 'static,
+{
+    /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
+    /// `*boxed` will be pinned in memory and unable to be moved.
+    ///
+    /// This conversion does not allocate on the heap and happens in place.
+    ///
+    /// This is also available via [`Box::into_pin`].
+    ///
+    /// Constructing and pinning a `Box` with <code><Pin<Box\<T>>>::from([Box::new]\(x))</code>
+    /// can also be written more concisely using <code>[Box::pin]\(x)</code>.
+    /// This `From` implementation is useful if you already have a `Box<T>`, or you are
+    /// constructing a (pinned) `Box` in a different way than with [`Box::new`].
+    fn from(b: Box<T, A>) -> Self {
+        Box::into_pin(b)
+    }
+}
+
+impl<T, A> Deref for Box<T, A>
+where
+    T: ?Sized,
+    A: Allocator,
+{
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized
+        // instance of `T`.
+        unsafe { self.0.as_ref() }
+    }
+}
+
+impl<T, A> DerefMut for Box<T, A>
+where
+    T: ?Sized,
+    A: Allocator,
+{
+    fn deref_mut(&mut self) -> &mut T {
+        // SAFETY: `self.0` is always properly aligned, dereferenceable and points to an initialized
+        // instance of `T`.
+        unsafe { self.0.as_mut() }
+    }
+}
+
+impl<T, A> fmt::Debug for Box<T, A>
+where
+    T: ?Sized + fmt::Debug,
+    A: Allocator,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T, A> Drop for Box<T, A>
+where
+    T: ?Sized,
+    A: Allocator,
+{
+    fn drop(&mut self) {
+        let ptr = self.0.as_ptr();
+
+        // SAFETY: We need to drop `self.0` in place, before we free the backing memory.
+        unsafe { core::ptr::drop_in_place(ptr) };
+
+        // SAFETY: `ptr` is always properly aligned, dereferenceable and points to an initialized
+        // instance of `T`.
+        if unsafe { core::mem::size_of_val(&*ptr) } != 0 {
+            // SAFETY: `ptr` was previously allocated with `A`.
+            unsafe { A::free(self.0.as_non_null().cast()) };
+        }
+    }
+}
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index 68605b633e73..b34c8127b76d 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -211,7 +211,7 @@
 //! [`pin_init!`]: crate::pin_init!
 
 use crate::{
-    alloc::{box_ext::BoxExt, AllocError, Flags},
+    alloc::{box_ext::BoxExt, AllocError, Flags, KBox},
     error::{self, Error},
     sync::UniqueArc,
     types::{Opaque, ScopeGuard},
@@ -1183,6 +1183,36 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
     }
 }
 
+impl<T> InPlaceInit<T> for KBox<T> {
+    #[inline]
+    fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = KBox::<_>::new_uninit(flags)?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid and will not be moved, because we pin it later.
+        unsafe { init.__pinned_init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() }.into())
+    }
+
+    #[inline]
+    fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
+    where
+        E: From<AllocError>,
+    {
+        let mut this = KBox::<_>::new_uninit(flags)?;
+        let slot = this.as_mut_ptr();
+        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
+        // slot is valid.
+        unsafe { init.__init(slot)? };
+        // SAFETY: All fields have been initialized.
+        Ok(unsafe { this.assume_init() })
+    }
+}
+
 impl<T> InPlaceInit<T> for UniqueArc<T> {
     #[inline]
     fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index b37a0b3180fb..39f9331a48e2 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,7 +14,7 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{box_ext::BoxExt, flags::*, vec_ext::VecExt};
+pub use crate::alloc::{box_ext::BoxExt, flags::*, vec_ext::VecExt, KBox, KVBox, VBox};
 
 #[doc(no_inline)]
 pub use alloc::{boxed::Box, vec::Vec};
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 9cd20fe41c20..dd602b2efd90 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,6 +2,7 @@
 
 //! Kernel types.
 
+use crate::alloc::Allocator;
 use crate::init::{self, PinInit};
 use alloc::boxed::Box;
 use core::{
@@ -89,6 +90,31 @@ unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
     }
 }
 
+impl<T: 'static, A> ForeignOwnable for crate::alloc::Box<T, A>
+where
+    A: Allocator,
+{
+    type Borrowed<'a> = &'a T;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        crate::alloc::Box::into_raw(self) as _
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
+        // SAFETY: The safety requirements for this function ensure that the object is still alive,
+        // so it is safe to dereference the raw pointer.
+        // The safety requirements of `from_foreign` also ensure that the object remains alive for
+        // the lifetime of the returned value.
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
+        // call to `Self::into_foreign`.
+        unsafe { crate::alloc::Box::from_raw(ptr as _) }
+    }
+}
+
 impl ForeignOwnable for () {
     type Borrowed<'a> = ();
 
-- 
2.45.2

[PATCH v2 10/23] rust: treewide: switch to our kernel `Box` type

[Danilo Krummrich]

Now that we got the kernel `Box` type in place, convert all existing
`Box` users to make use of it.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/init.rs               | 39 ++++++++++++++++---------------
 rust/kernel/init/__internal.rs    |  2 +-
 rust/kernel/sync/arc.rs           | 17 +++++++-------
 rust/kernel/sync/condvar.rs       |  4 ++--
 rust/kernel/sync/lock/mutex.rs    |  2 +-
 rust/kernel/sync/lock/spinlock.rs |  2 +-
 rust/kernel/workqueue.rs          | 20 ++++++++--------
 7 files changed, 43 insertions(+), 43 deletions(-)

diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index b34c8127b76d..f50b9bfe660f 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -68,7 +68,7 @@
 //! #     a <- new_mutex!(42, "Foo::a"),
 //! #     b: 24,
 //! # });
-//! let foo: Result<Pin<Box<Foo>>> = Box::pin_init(foo, GFP_KERNEL);
+//! let foo: Result<Pin<KBox<Foo>>> = KBox::pin_init(foo, GFP_KERNEL);
 //! ```
 //!
 //! For more information see the [`pin_init!`] macro.
@@ -93,14 +93,14 @@
 //! struct DriverData {
 //!     #[pin]
 //!     status: Mutex<i32>,
-//!     buffer: Box<[u8; 1_000_000]>,
+//!     buffer: KBox<[u8; 1_000_000]>,
 //! }
 //!
 //! impl DriverData {
 //!     fn new() -> impl PinInit<Self, Error> {
 //!         try_pin_init!(Self {
 //!             status <- new_mutex!(0, "DriverData::status"),
-//!             buffer: Box::init(kernel::init::zeroed(), GFP_KERNEL)?,
+//!             buffer: KBox::init(kernel::init::zeroed(), GFP_KERNEL)?,
 //!         })
 //!     }
 //! }
@@ -297,7 +297,7 @@ macro_rules! stack_pin_init {
 /// struct Foo {
 ///     #[pin]
 ///     a: Mutex<usize>,
-///     b: Box<Bar>,
+///     b: KBox<Bar>,
 /// }
 ///
 /// struct Bar {
@@ -306,7 +306,7 @@ macro_rules! stack_pin_init {
 ///
 /// stack_try_pin_init!(let foo: Result<Pin<&mut Foo>, AllocError> = pin_init!(Foo {
 ///     a <- new_mutex!(42),
-///     b: Box::new(Bar {
+///     b: KBox::new(Bar {
 ///         x: 64,
 ///     }, GFP_KERNEL)?,
 /// }));
@@ -323,7 +323,7 @@ macro_rules! stack_pin_init {
 /// struct Foo {
 ///     #[pin]
 ///     a: Mutex<usize>,
-///     b: Box<Bar>,
+///     b: KBox<Bar>,
 /// }
 ///
 /// struct Bar {
@@ -332,7 +332,7 @@ macro_rules! stack_pin_init {
 ///
 /// stack_try_pin_init!(let foo: Pin<&mut Foo> =? pin_init!(Foo {
 ///     a <- new_mutex!(42),
-///     b: Box::new(Bar {
+///     b: KBox::new(Bar {
 ///         x: 64,
 ///     }, GFP_KERNEL)?,
 /// }));
@@ -391,7 +391,7 @@ macro_rules! stack_try_pin_init {
 ///     },
 /// });
 /// # initializer }
-/// # Box::pin_init(demo(), GFP_KERNEL).unwrap();
+/// # KBox::pin_init(demo(), GFP_KERNEL).unwrap();
 /// ```
 ///
 /// Arbitrary Rust expressions can be used to set the value of a variable.
@@ -461,7 +461,7 @@ macro_rules! stack_try_pin_init {
 /// #         })
 /// #     }
 /// # }
-/// let foo = Box::pin_init(Foo::new(), GFP_KERNEL);
+/// let foo = KBox::pin_init(Foo::new(), GFP_KERNEL);
 /// ```
 ///
 /// They can also easily embed it into their own `struct`s:
@@ -593,7 +593,7 @@ macro_rules! pin_init {
 /// use kernel::{init::{self, PinInit}, error::Error};
 /// #[pin_data]
 /// struct BigBuf {
-///     big: Box<[u8; 1024 * 1024 * 1024]>,
+///     big: KBox<[u8; 1024 * 1024 * 1024]>,
 ///     small: [u8; 1024 * 1024],
 ///     ptr: *mut u8,
 /// }
@@ -601,7 +601,7 @@ macro_rules! pin_init {
 /// impl BigBuf {
 ///     fn new() -> impl PinInit<Self, Error> {
 ///         try_pin_init!(Self {
-///             big: Box::init(init::zeroed(), GFP_KERNEL)?,
+///             big: KBox::init(init::zeroed(), GFP_KERNEL)?,
 ///             small: [0; 1024 * 1024],
 ///             ptr: core::ptr::null_mut(),
 ///         }? Error)
@@ -693,16 +693,16 @@ macro_rules! init {
 /// # Examples
 ///
 /// ```rust
-/// use kernel::{init::{PinInit, zeroed}, error::Error};
+/// use kernel::{alloc::KBox, init::{PinInit, zeroed}, error::Error};
 /// struct BigBuf {
-///     big: Box<[u8; 1024 * 1024 * 1024]>,
+///     big: KBox<[u8; 1024 * 1024 * 1024]>,
 ///     small: [u8; 1024 * 1024],
 /// }
 ///
 /// impl BigBuf {
 ///     fn new() -> impl Init<Self, Error> {
 ///         try_init!(Self {
-///             big: Box::init(zeroed(), GFP_KERNEL)?,
+///             big: KBox::init(zeroed(), GFP_KERNEL)?,
 ///             small: [0; 1024 * 1024],
 ///         }? Error)
 ///     }
@@ -825,7 +825,7 @@ fn pin_chain<F>(self, f: F) -> ChainPinInit<Self, F, T, E>
 }
 
 /// An initializer returned by [`PinInit::pin_chain`].
-pub struct ChainPinInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, Box<T>)>);
+pub struct ChainPinInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, KBox<T>)>);
 
 // SAFETY: The `__pinned_init` function is implemented such that it
 // - returns `Ok(())` on successful initialization,
@@ -927,7 +927,7 @@ fn chain<F>(self, f: F) -> ChainInit<Self, F, T, E>
 }
 
 /// An initializer returned by [`Init::chain`].
-pub struct ChainInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, Box<T>)>);
+pub struct ChainInit<I, F, T: ?Sized, E>(I, F, __internal::Invariant<(E, KBox<T>)>);
 
 // SAFETY: The `__init` function is implemented such that it
 // - returns `Ok(())` on successful initialization,
@@ -1013,8 +1013,9 @@ pub fn uninit<T, E>() -> impl Init<MaybeUninit<T>, E> {
 /// # Examples
 ///
 /// ```rust
-/// use kernel::{error::Error, init::init_array_from_fn};
-/// let array: Box<[usize; 1_000]> = Box::init::<Error>(init_array_from_fn(|i| i), GFP_KERNEL).unwrap();
+/// use kernel::{alloc::KBox, error::Error, init::init_array_from_fn};
+/// let array: KBox<[usize; 1_000]> =
+///     KBox::init::<Error>(init_array_from_fn(|i| i), GFP_KERNEL).unwrap();
 /// assert_eq!(array.len(), 1_000);
 /// ```
 pub fn init_array_from_fn<I, const N: usize, T, E>(
@@ -1351,7 +1352,7 @@ macro_rules! impl_zeroable {
     //
     // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant.
     {<T: ?Sized>} Option<NonNull<T>>,
-    {<T: ?Sized>} Option<Box<T>>,
+    {<T: ?Sized>} Option<KBox<T>>,
 
     // SAFETY: `null` pointer is valid.
     //
diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal.rs
index db3372619ecd..dfb2204918c7 100644
--- a/rust/kernel/init/__internal.rs
+++ b/rust/kernel/init/__internal.rs
@@ -102,7 +102,7 @@ fn make_closure<F, O, E>(self, f: F) -> F
     }
 }
 
-pub struct AllData<T: ?Sized>(PhantomData<fn(Box<T>) -> Box<T>>);
+pub struct AllData<T: ?Sized>(PhantomData<fn(KBox<T>) -> KBox<T>>);
 
 impl<T: ?Sized> Clone for AllData<T> {
     fn clone(&self) -> Self {
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index 3673496c2363..b5c84995d7d2 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -16,13 +16,12 @@
 //! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 
 use crate::{
-    alloc::{box_ext::BoxExt, AllocError, Flags},
+    alloc::{AllocError, Flags, KBox},
     error::{self, Error},
     init::{self, InPlaceInit, Init, PinInit},
     try_init,
     types::{ForeignOwnable, Opaque},
 };
-use alloc::boxed::Box;
 use core::{
     alloc::Layout,
     fmt,
@@ -203,11 +202,11 @@ pub fn new(contents: T, flags: Flags) -> Result<Self, AllocError> {
             data: contents,
         };
 
-        let inner = <Box<_> as BoxExt<_>>::new(value, flags)?;
+        let inner = KBox::new(value, flags)?;
 
         // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
         // `Arc` object.
-        Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
+        Ok(unsafe { Self::from_inner(KBox::leak(inner).into()) })
     }
 
     /// Use the given initializer to in-place initialize a `T`.
@@ -422,8 +421,8 @@ fn drop(&mut self) {
         if is_zero {
             // The count reached zero, we must free the memory.
             //
-            // SAFETY: The pointer was initialised from the result of `Box::leak`.
-            unsafe { drop(Box::from_raw(self.ptr.as_ptr())) };
+            // SAFETY: The pointer was initialised from the result of `KBox::leak`.
+            unsafe { drop(KBox::from_raw(self.ptr.as_ptr())) };
         }
     }
 }
@@ -668,7 +667,7 @@ pub fn new(value: T, flags: Flags) -> Result<Self, AllocError> {
     /// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
     pub fn new_uninit(flags: Flags) -> Result<UniqueArc<MaybeUninit<T>>, AllocError> {
         // INVARIANT: The refcount is initialised to a non-zero value.
-        let inner = Box::try_init::<AllocError>(
+        let inner = KBox::try_init::<AllocError>(
             try_init!(ArcInner {
                 // SAFETY: There are no safety requirements for this FFI call.
                 refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
@@ -678,8 +677,8 @@ pub fn new_uninit(flags: Flags) -> Result<UniqueArc<MaybeUninit<T>>, AllocError>
         )?;
         Ok(UniqueArc {
             // INVARIANT: The newly-created object has a refcount of 1.
-            // SAFETY: The pointer from the `Box` is valid.
-            inner: unsafe { Arc::from_inner(Box::leak(inner).into()) },
+            // SAFETY: The pointer from the `KBox` is valid.
+            inner: unsafe { Arc::from_inner(KBox::leak(inner).into()) },
         })
     }
 }
diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
index 2b306afbe56d..2081932bb4b9 100644
--- a/rust/kernel/sync/condvar.rs
+++ b/rust/kernel/sync/condvar.rs
@@ -70,8 +70,8 @@ macro_rules! new_condvar {
 /// }
 ///
 /// /// Allocates a new boxed `Example`.
-/// fn new_example() -> Result<Pin<Box<Example>>> {
-///     Box::pin_init(pin_init!(Example {
+/// fn new_example() -> Result<Pin<KBox<Example>>> {
+///     KBox::pin_init(pin_init!(Example {
 ///         value <- new_mutex!(0),
 ///         value_changed <- new_condvar!(),
 ///     }), GFP_KERNEL)
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 30632070ee67..f8f6d530db7d 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -58,7 +58,7 @@ macro_rules! new_mutex {
 /// }
 ///
 /// // Allocate a boxed `Example`.
-/// let e = Box::pin_init(Example::new(), GFP_KERNEL)?;
+/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
 /// assert_eq!(e.c, 10);
 /// assert_eq!(e.d.lock().a, 20);
 /// assert_eq!(e.d.lock().b, 30);
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index ea5c5bc1ce12..a9096a4dc42a 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -56,7 +56,7 @@ macro_rules! new_spinlock {
 /// }
 ///
 /// // Allocate a boxed `Example`.
-/// let e = Box::pin_init(Example::new(), GFP_KERNEL)?;
+/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
 /// assert_eq!(e.c, 10);
 /// assert_eq!(e.d.lock().a, 20);
 /// assert_eq!(e.d.lock().b, 30);
diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
index 1cec63a2aea8..47c8a3df0b8b 100644
--- a/rust/kernel/workqueue.rs
+++ b/rust/kernel/workqueue.rs
@@ -216,7 +216,7 @@ pub fn try_spawn<T: 'static + Send + FnOnce()>(
             func: Some(func),
         });
 
-        self.enqueue(Box::pin_init(init, flags).map_err(|_| AllocError)?);
+        self.enqueue(KBox::pin_init(init, flags).map_err(|_| AllocError)?);
         Ok(())
     }
 }
@@ -239,9 +239,9 @@ fn project(self: Pin<&mut Self>) -> &mut Option<T> {
 }
 
 impl<T: FnOnce()> WorkItem for ClosureWork<T> {
-    type Pointer = Pin<Box<Self>>;
+    type Pointer = Pin<KBox<Self>>;
 
-    fn run(mut this: Pin<Box<Self>>) {
+    fn run(mut this: Pin<KBox<Self>>) {
         if let Some(func) = this.as_mut().project().take() {
             (func)()
         }
@@ -297,7 +297,7 @@ unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput
 
 /// Defines the method that should be called directly when a work item is executed.
 ///
-/// This trait is implemented by `Pin<Box<T>>` and [`Arc<T>`], and is mainly intended to be
+/// This trait is implemented by `Pin<KBox<T>>` and [`Arc<T>`], and is mainly intended to be
 /// implemented for smart pointer types. For your own structs, you would implement [`WorkItem`]
 /// instead. The [`run`] method on this trait will usually just perform the appropriate
 /// `container_of` translation and then call into the [`run`][WorkItem::run] method from the
@@ -329,7 +329,7 @@ pub unsafe trait WorkItemPointer<const ID: u64>: RawWorkItem<ID> {
 /// This trait is used when the `work_struct` field is defined using the [`Work`] helper.
 pub trait WorkItem<const ID: u64 = 0> {
     /// The pointer type that this struct is wrapped in. This will typically be `Arc<Self>` or
-    /// `Pin<Box<Self>>`.
+    /// `Pin<KBox<Self>>`.
     type Pointer: WorkItemPointer<ID>;
 
     /// The method that should be called when this work item is executed.
@@ -563,7 +563,7 @@ unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput
     }
 }
 
-unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Pin<Box<T>>
+unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Pin<KBox<T>>
 where
     T: WorkItem<ID, Pointer = Self>,
     T: HasWork<T, ID>,
@@ -574,7 +574,7 @@ unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Pin<Box<T>>
         // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`.
         let ptr = unsafe { T::work_container_of(ptr) };
         // SAFETY: This pointer comes from `Arc::into_raw` and we've been given back ownership.
-        let boxed = unsafe { Box::from_raw(ptr) };
+        let boxed = unsafe { KBox::from_raw(ptr) };
         // SAFETY: The box was already pinned when it was enqueued.
         let pinned = unsafe { Pin::new_unchecked(boxed) };
 
@@ -582,7 +582,7 @@ unsafe impl<T, const ID: u64> WorkItemPointer<ID> for Pin<Box<T>>
     }
 }
 
-unsafe impl<T, const ID: u64> RawWorkItem<ID> for Pin<Box<T>>
+unsafe impl<T, const ID: u64> RawWorkItem<ID> for Pin<KBox<T>>
 where
     T: WorkItem<ID, Pointer = Self>,
     T: HasWork<T, ID>,
@@ -596,9 +596,9 @@ unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput
         // SAFETY: We're not going to move `self` or any of its fields, so its okay to temporarily
         // remove the `Pin` wrapper.
         let boxed = unsafe { Pin::into_inner_unchecked(self) };
-        let ptr = Box::into_raw(boxed);
+        let ptr = KBox::into_raw(boxed);
 
-        // SAFETY: Pointers into a `Box` point at a valid value.
+        // SAFETY: Pointers into a `KBox` point at a valid value.
         let work_ptr = unsafe { T::raw_get_work(ptr) };
         // SAFETY: `raw_get_work` returns a pointer to a valid value.
         let work_ptr = unsafe { Work::raw_get(work_ptr) };
-- 
2.45.2

[PATCH v2 11/23] rust: alloc: remove `BoxExt` extension

[Danilo Krummrich]

Now that all existing `Box` users were moved to the kernel `Box` type,
remove the `BoxExt` extension.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs         |  1 -
 rust/kernel/alloc/box_ext.rs | 56 ------------------------------------
 rust/kernel/init.rs          | 34 +---------------------
 rust/kernel/lib.rs           |  1 -
 rust/kernel/prelude.rs       |  4 +--
 rust/kernel/types.rs         | 22 --------------
 6 files changed, 3 insertions(+), 115 deletions(-)
 delete mode 100644 rust/kernel/alloc/box_ext.rs

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index d9809368643e..48c008ab340d 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -4,7 +4,6 @@
 
 #[cfg(not(any(test, testlib)))]
 pub mod allocator;
-pub mod box_ext;
 pub mod kbox;
 pub mod vec_ext;
 
diff --git a/rust/kernel/alloc/box_ext.rs b/rust/kernel/alloc/box_ext.rs
deleted file mode 100644
index 829cb1c1cf9e..000000000000
--- a/rust/kernel/alloc/box_ext.rs
+++ /dev/null
@@ -1,56 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-
-//! Extensions to [`Box`] for fallible allocations.
-
-use super::{AllocError, Flags};
-use alloc::boxed::Box;
-use core::mem::MaybeUninit;
-
-/// Extensions to [`Box`].
-pub trait BoxExt<T>: Sized {
-    /// Allocates a new box.
-    ///
-    /// The allocation may fail, in which case an error is returned.
-    fn new(x: T, flags: Flags) -> Result<Self, AllocError>;
-
-    /// Allocates a new uninitialised box.
-    ///
-    /// The allocation may fail, in which case an error is returned.
-    fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError>;
-}
-
-impl<T> BoxExt<T> for Box<T> {
-    fn new(x: T, flags: Flags) -> Result<Self, AllocError> {
-        let b = <Self as BoxExt<_>>::new_uninit(flags)?;
-        Ok(Box::write(b, x))
-    }
-
-    #[cfg(any(test, testlib))]
-    fn new_uninit(_flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError> {
-        Ok(Box::new_uninit())
-    }
-
-    #[cfg(not(any(test, testlib)))]
-    fn new_uninit(flags: Flags) -> Result<Box<MaybeUninit<T>>, AllocError> {
-        let ptr = if core::mem::size_of::<MaybeUninit<T>>() == 0 {
-            core::ptr::NonNull::<_>::dangling().as_ptr()
-        } else {
-            let layout = core::alloc::Layout::new::<MaybeUninit<T>>();
-
-            // SAFETY: Memory is being allocated (first arg is null). The only other source of
-            // safety issues is sleeping on atomic context, which is addressed by klint. Lastly,
-            // the type is not a SZT (checked above).
-            let ptr =
-                unsafe { super::allocator::krealloc_aligned(core::ptr::null_mut(), layout, flags) };
-            if ptr.is_null() {
-                return Err(AllocError);
-            }
-
-            ptr.cast::<MaybeUninit<T>>()
-        };
-
-        // SAFETY: For non-zero-sized types, we allocate above using the global allocator. For
-        // zero-sized types, we use `NonNull::dangling`.
-        Ok(unsafe { Box::from_raw(ptr) })
-    }
-}
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index f50b9bfe660f..a1cd7ced70f9 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -211,12 +211,11 @@
 //! [`pin_init!`]: crate::pin_init!
 
 use crate::{
-    alloc::{box_ext::BoxExt, AllocError, Flags, KBox},
+    alloc::{AllocError, Flags, KBox},
     error::{self, Error},
     sync::UniqueArc,
     types::{Opaque, ScopeGuard},
 };
-use alloc::boxed::Box;
 use core::{
     cell::UnsafeCell,
     convert::Infallible,
@@ -589,7 +588,6 @@ macro_rules! pin_init {
 /// # Examples
 ///
 /// ```rust
-/// # #![feature(new_uninit)]
 /// use kernel::{init::{self, PinInit}, error::Error};
 /// #[pin_data]
 /// struct BigBuf {
@@ -1154,36 +1152,6 @@ fn init<E>(init: impl Init<T, E>, flags: Flags) -> error::Result<Self>
     }
 }
 
-impl<T> InPlaceInit<T> for Box<T> {
-    #[inline]
-    fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
-    where
-        E: From<AllocError>,
-    {
-        let mut this = <Box<_> as BoxExt<_>>::new_uninit(flags)?;
-        let slot = this.as_mut_ptr();
-        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
-        // slot is valid and will not be moved, because we pin it later.
-        unsafe { init.__pinned_init(slot)? };
-        // SAFETY: All fields have been initialized.
-        Ok(unsafe { this.assume_init() }.into())
-    }
-
-    #[inline]
-    fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
-    where
-        E: From<AllocError>,
-    {
-        let mut this = <Box<_> as BoxExt<_>>::new_uninit(flags)?;
-        let slot = this.as_mut_ptr();
-        // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
-        // slot is valid.
-        unsafe { init.__init(slot)? };
-        // SAFETY: All fields have been initialized.
-        Ok(unsafe { this.assume_init() })
-    }
-}
-
 impl<T> InPlaceInit<T> for KBox<T> {
     #[inline]
     fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Pin<Self>, E>
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 2cf7c6b6f66b..6ae20a23de46 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -14,7 +14,6 @@
 #![no_std]
 #![feature(coerce_unsized)]
 #![feature(dispatch_from_dyn)]
-#![feature(new_uninit)]
 #![feature(receiver_trait)]
 #![feature(unsize)]
 
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 39f9331a48e2..a8018ef2e691 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,10 +14,10 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{box_ext::BoxExt, flags::*, vec_ext::VecExt, KBox, KVBox, VBox};
+pub use crate::alloc::{flags::*, vec_ext::VecExt, KBox, KVBox, VBox};
 
 #[doc(no_inline)]
-pub use alloc::{boxed::Box, vec::Vec};
+pub use alloc::vec::Vec;
 
 #[doc(no_inline)]
 pub use macros::{module, pin_data, pinned_drop, vtable, Zeroable};
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index dd602b2efd90..d67b37a5edb8 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -4,7 +4,6 @@
 
 use crate::alloc::Allocator;
 use crate::init::{self, PinInit};
-use alloc::boxed::Box;
 use core::{
     cell::UnsafeCell,
     marker::{PhantomData, PhantomPinned},
@@ -68,27 +67,6 @@ unsafe fn try_from_foreign(ptr: *const core::ffi::c_void) -> Option<Self> {
     }
 }
 
-impl<T: 'static> ForeignOwnable for Box<T> {
-    type Borrowed<'a> = &'a T;
-
-    fn into_foreign(self) -> *const core::ffi::c_void {
-        Box::into_raw(self) as _
-    }
-
-    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
-        // SAFETY: The safety requirements for this function ensure that the object is still alive,
-        // so it is safe to dereference the raw pointer.
-        // The safety requirements of `from_foreign` also ensure that the object remains alive for
-        // the lifetime of the returned value.
-        unsafe { &*ptr.cast() }
-    }
-
-    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
-        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
-        // call to `Self::into_foreign`.
-        unsafe { Box::from_raw(ptr as _) }
-    }
-}
 
 impl<T: 'static, A> ForeignOwnable for crate::alloc::Box<T, A>
 where
-- 
2.45.2

[PATCH v2 12/23] rust: alloc: add `Box` to prelude

[Danilo Krummrich]

Now that we removed `BoxExt` and the corresponding includes in
prelude.rs, add the new kernel `Box` type instead.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/prelude.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index a8018ef2e691..6bf77577eae7 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,7 +14,7 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{flags::*, vec_ext::VecExt, KBox, KVBox, VBox};
+pub use crate::alloc::{flags::*, vec_ext::VecExt, Box, KBox, KVBox, VBox};
 
 #[doc(no_inline)]
 pub use alloc::vec::Vec;
-- 
2.45.2

[PATCH v2 13/23] rust: alloc: import kernel `Box` type in types.rs

[Danilo Krummrich]

Now that we removed `BoxExt` and the corresponding includes in
types.rs, add the new kernel `Box` type instead.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/types.rs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index d67b37a5edb8..ee0063a20d89 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,7 +2,7 @@
 
 //! Kernel types.
 
-use crate::alloc::Allocator;
+use crate::alloc::{Allocator, Box};
 use crate::init::{self, PinInit};
 use core::{
     cell::UnsafeCell,
@@ -67,15 +67,14 @@ unsafe fn try_from_foreign(ptr: *const core::ffi::c_void) -> Option<Self> {
     }
 }
 
-
-impl<T: 'static, A> ForeignOwnable for crate::alloc::Box<T, A>
+impl<T: 'static, A> ForeignOwnable for Box<T, A>
 where
     A: Allocator,
 {
     type Borrowed<'a> = &'a T;
 
     fn into_foreign(self) -> *const core::ffi::c_void {
-        crate::alloc::Box::into_raw(self) as _
+        Box::into_raw(self) as _
     }
 
     unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
@@ -89,7 +88,7 @@ unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
     unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
         // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
         // call to `Self::into_foreign`.
-        unsafe { crate::alloc::Box::from_raw(ptr as _) }
+        unsafe { Box::from_raw(ptr as _) }
     }
 }
 
-- 
2.45.2

[PATCH v2 14/23] rust: alloc: implement kernel `Vec` type

[Danilo Krummrich]

`Vec` provides a contiguous growable array type (such as `Vec`) with
contents allocated with the kernel's allocators (e.g. `Kmalloc`,
`Vmalloc` or `KVmalloc`).

In contrast to Rust's `Vec` type, the kernel `Vec` type considers the
kernel's GFP flags for all appropriate functions, always reports
allocation failures through `Result<_, AllocError>` and remains
independent from unstable features.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs      |   6 +
 rust/kernel/alloc/kbox.rs |  16 +-
 rust/kernel/alloc/kvec.rs | 580 ++++++++++++++++++++++++++++++++++++++
 rust/kernel/prelude.rs    |   2 +-
 4 files changed, 602 insertions(+), 2 deletions(-)
 create mode 100644 rust/kernel/alloc/kvec.rs

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 48c008ab340d..827922e1f1d1 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -5,6 +5,7 @@
 #[cfg(not(any(test, testlib)))]
 pub mod allocator;
 pub mod kbox;
+pub mod kvec;
 pub mod vec_ext;
 
 #[cfg(any(test, testlib))]
@@ -18,6 +19,11 @@
 pub use self::kbox::KVBox;
 pub use self::kbox::VBox;
 
+pub use self::kvec::KVVec;
+pub use self::kvec::KVec;
+pub use self::kvec::VVec;
+pub use self::kvec::Vec;
+
 /// Indicates an allocation error.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct AllocError;
diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index eb4a5ff500b8..d7b0b790a424 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -2,7 +2,7 @@
 
 //! Implementation of [`Box`].
 
-use super::{AllocError, Allocator, Flags};
+use super::{AllocError, Allocator, Flags, Vec};
 use core::fmt;
 use core::marker::PhantomData;
 use core::mem::ManuallyDrop;
@@ -173,6 +173,20 @@ pub fn into_pin(b: Self) -> Pin<Self>
     }
 }
 
+impl<T, A, const N: usize> Box<[T; N], A>
+where
+    A: Allocator,
+{
+    /// Convert a `Box<[T], A>` to a `Vec<T, A>`.
+    pub fn into_vec(self) -> Vec<T, A> {
+        let len = self.len();
+        unsafe {
+            let ptr = self.into_raw();
+            Vec::from_raw_parts(ptr as _, len, len)
+        }
+    }
+}
+
 impl<T, A> Box<MaybeUninit<T>, A>
 where
     A: Allocator,
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
new file mode 100644
index 000000000000..58b3f679ad83
--- /dev/null
+++ b/rust/kernel/alloc/kvec.rs
@@ -0,0 +1,580 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Implementation of [`Vec`].
+
+use super::{AllocError, Allocator, Flags};
+use crate::types::Unique;
+use core::{
+    fmt,
+    marker::PhantomData,
+    mem::{ManuallyDrop, MaybeUninit},
+    ops::Deref,
+    ops::DerefMut,
+    ops::Index,
+    ops::IndexMut,
+    ptr, slice,
+    slice::SliceIndex,
+};
+
+/// Create a [`Vec`] containing the arguments.
+///
+/// # Examples
+///
+/// ```
+/// let mut v = kernel::kvec![];
+/// v.push(1, GFP_KERNEL)?;
+/// assert_eq!(v, [1]);
+///
+/// let mut v = kernel::kvec![1; 3]?;
+/// v.push(4, GFP_KERNEL)?;
+/// assert_eq!(v, [1, 1, 1, 4]);
+///
+/// let mut v = kernel::kvec![1, 2, 3]?;
+/// v.push(4, GFP_KERNEL)?;
+/// assert_eq!(v, [1, 2, 3, 4]);
+///
+/// # Ok::<(), Error>(())
+/// ```
+#[macro_export]
+macro_rules! kvec {
+    () => (
+        {
+            $crate::alloc::KVec::new()
+        }
+    );
+    ($elem:expr; $n:expr) => (
+        {
+            $crate::alloc::KVec::from_elem($elem, $n, GFP_KERNEL)
+        }
+    );
+    ($($x:expr),+ $(,)?) => (
+        {
+            match $crate::alloc::KBox::new([$($x),+], GFP_KERNEL) {
+                Ok(b) => Ok($crate::alloc::KBox::into_vec(b)),
+                Err(e) => Err(e),
+            }
+        }
+    );
+}
+
+/// The kernel's `Vec` type named [`Vec`].
+///
+/// A contiguous growable array type with contents allocated with the kernel's allocators (e.g.
+/// `Kmalloc`, `Vmalloc` or `KVmalloc`, written `Vec<T, A>`.
+///
+/// For non-zero-sized values, a [`Vec`] will use the given allocator `A` for its allocation. For
+/// the most common allocators the type aliases `KVec`, `VVec` and `KVVec` exist.
+///
+/// For zero-sized types the [`Vec`]'s pointer must be `dangling_mut::<T>`; no memory is allocated.
+///
+/// Generally, [`Vec`] consists of a pointer that represents the vector's backing buffer, the
+/// capacity of the vector (the number of elements that currently fit into the vector), it's length
+/// (the number of elements that are currently stored in the vector) and the `Allocator` used to
+/// allocate (and free) the backing buffer.
+///
+/// A [`Vec`] can be deconstructed into and (re-)constructed from it's previously named raw parts
+/// and manually modified.
+///
+/// [`Vec`]'s backing buffer gets, if required, automatically increased (re-allocated) when elements
+/// are added to the vector.
+///
+/// # Invariants
+///
+/// The [`Vec`] backing buffer's pointer always properly aligned and either points to memory
+/// allocated with `A` or, for zero-sized types, is a dangling pointer.
+///
+/// The length of the vector always represents the exact number of elements stored in the vector.
+///
+/// The capacity of the vector always represents the absolute number of elements that can be stored
+/// within the vector without re-allocation. However, it is legal for the backing buffer to be
+/// larger than `size_of<T>` times the capacity.
+///
+/// The `Allocator` of the vector is the exact allocator the backing buffer was allocated with (and
+/// must be freed with).
+pub struct Vec<T, A: Allocator> {
+    ptr: Unique<T>,
+    /// Never used for ZSTs; it's `capacity()`'s responsibility to return usize::MAX in that case.
+    ///
+    /// # Safety
+    ///
+    /// `cap` must be in the `0..=isize::MAX` range.
+    cap: usize,
+    len: usize,
+    _p: PhantomData<A>,
+}
+
+/// Type alias for `Vec` with a `Kmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let mut v = KVec::new();
+/// v.push(1, GFP_KERNEL)?;
+/// assert_eq!(&v, &[1]);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type KVec<T> = Vec<T, super::allocator::Kmalloc>;
+
+/// Type alias for `Vec` with a `Vmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let mut v = VVec::new();
+/// v.push(1, GFP_KERNEL)?;
+/// assert_eq!(&v, &[1]);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type VVec<T> = Vec<T, super::allocator::Vmalloc>;
+
+/// Type alias for `Vec` with a `KVmalloc` allocator.
+///
+/// # Examples
+///
+/// ```
+/// let mut v = KVVec::new();
+/// v.push(1, GFP_KERNEL)?;
+/// assert_eq!(&v, &[1]);
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub type KVVec<T> = Vec<T, super::allocator::KVmalloc>;
+
+impl<T, A> Vec<T, A>
+where
+    A: Allocator,
+{
+    #[inline]
+    fn is_zst() -> bool {
+        core::mem::size_of::<T>() == 0
+    }
+
+    /// Returns a reference to the underlying allocator.
+    #[inline]
+    pub fn allocator(&self) -> &PhantomData<A> {
+        &self._p
+    }
+
+    /// Returns the total number of elements the vector can hold without
+    /// reallocating.
+    pub fn capacity(&self) -> usize {
+        if Self::is_zst() {
+            usize::MAX
+        } else {
+            self.cap
+        }
+    }
+
+    /// Returns the number of elements in the vector, also referred to
+    /// as its 'length'.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Forces the length of the vector to new_len.
+    ///
+    /// # Safety
+    ///
+    /// - `new_len` must be less than or equal to [`Self::capacity()`].
+    /// - The elements at `old_len..new_len` must be initialized.
+    #[inline]
+    pub unsafe fn set_len(&mut self, new_len: usize) {
+        self.len = new_len;
+    }
+
+    /// Extracts a slice containing the entire vector.
+    ///
+    /// Equivalent to `&s[..]`.
+    #[inline]
+    pub fn as_slice(&self) -> &[T] {
+        self
+    }
+
+    /// Extracts a mutable slice of the entire vector.
+    ///
+    /// Equivalent to `&mut s[..]`.
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+
+    /// Returns an unsafe mutable pointer to the vector's buffer, or a dangling
+    /// raw pointer valid for zero sized reads if the vector didn't allocate.
+    #[inline]
+    pub fn as_mut_ptr(&self) -> *mut T {
+        self.ptr.as_ptr()
+    }
+
+    /// Returns a raw pointer to the slice's buffer.
+    #[inline]
+    pub fn as_ptr(&self) -> *const T {
+        self.as_mut_ptr()
+    }
+
+    /// Returns `true` if the vector contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = KVec::new();
+    /// assert!(v.is_empty());
+    ///
+    /// v.push(1, GFP_KERNEL);
+    /// assert!(!v.is_empty());
+    /// ```
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Like `new`, but parameterized over the choice of allocator for the returned `Vec`.
+    #[inline]
+    pub const fn new() -> Self {
+        Self {
+            ptr: Unique::dangling(),
+            cap: 0,
+            len: 0,
+            _p: PhantomData::<A>,
+        }
+    }
+
+    fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] {
+        // Note:
+        // This method is not implemented in terms of `split_at_spare_mut`,
+        // to prevent invalidation of pointers to the buffer.
+        unsafe {
+            slice::from_raw_parts_mut(
+                self.as_mut_ptr().add(self.len) as *mut MaybeUninit<T>,
+                self.capacity() - self.len,
+            )
+        }
+    }
+
+    /// Appends an element to the back of the [`Vec`] instance.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = KVec::new();
+    /// v.push(1, GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1]);
+    ///
+    /// v.push(2, GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1, 2]);
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
+        Vec::reserve(self, 1, flags)?;
+        let s = self.spare_capacity_mut();
+        s[0].write(v);
+
+        // SAFETY: We just initialised the first spare entry, so it is safe to increase the length
+        // by 1. We also know that the new length is <= capacity because of the previous call to
+        // `reserve` above.
+        unsafe { self.set_len(self.len() + 1) };
+        Ok(())
+    }
+
+    /// Creates a new [`Vec`] instance with at least the given capacity.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = KVec::<u32>::with_capacity(20, GFP_KERNEL)?;
+    ///
+    /// assert!(v.capacity() >= 20);
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn with_capacity(capacity: usize, flags: Flags) -> Result<Self, AllocError> {
+        let mut v = Vec::new();
+
+        Self::reserve(&mut v, capacity, flags)?;
+
+        Ok(v)
+    }
+
+    /// Pushes clones of the elements of slice into the [`Vec`] instance.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = KVec::new();
+    /// v.push(1, GFP_KERNEL)?;
+    ///
+    /// v.extend_from_slice(&[20, 30, 40], GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1, 20, 30, 40]);
+    ///
+    /// v.extend_from_slice(&[50, 60], GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1, 20, 30, 40, 50, 60]);
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn extend_from_slice(&mut self, other: &[T], flags: Flags) -> Result<(), AllocError>
+    where
+        T: Clone,
+    {
+        self.reserve(other.len(), flags)?;
+        for (slot, item) in core::iter::zip(self.spare_capacity_mut(), other) {
+            slot.write(item.clone());
+        }
+
+        // SAFETY: We just initialised the `other.len()` spare entries, so it is safe to increase
+        // the length by the same amount. We also know that the new length is <= capacity because
+        // of the previous call to `reserve` above.
+        unsafe { self.set_len(self.len() + other.len()) };
+        Ok(())
+    }
+
+    /// Creates a Vec<T, A> directly from a pointer, a length, a capacity, and an allocator.
+    ///
+    /// # Safety
+    ///
+    /// This is highly unsafe, due to the number of invariants that aren’t checked:
+    ///
+    /// - `ptr` must be currently allocated via the given allocator `alloc`.
+    /// - `T` needs to have the same alignment as what `ptr` was allocated with. (`T` having a less
+    ///   strict alignment is not sufficient, the alignment really needs to be equal to satisfy the
+    ///   `dealloc` requirement that memory must be allocated and deallocated with the same layout.)
+    /// - The size of `T` times the `capacity` (i.e. the allocated size in bytes) needs to be
+    ///   smaller or equal the size the pointer was allocated with.
+    /// - `length` needs to be less than or equal to `capacity`.
+    /// - The first `length` values must be properly initialized values of type `T`.
+    /// - The allocated size in bytes must be no larger than `isize::MAX`. See the safety
+    ///   documentation of `pointer::offset`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = kernel::kvec![1, 2, 3]?;
+    /// v.reserve(1, GFP_KERNEL)?;
+    ///
+    /// let (mut ptr, mut len, cap) = v.into_raw_parts();
+    ///
+    /// unsafe { ptr.add(len).write(4) };
+    /// len += 1;
+    ///
+    /// let v = unsafe { KVec::from_raw_parts(ptr, len, cap) };
+    ///
+    /// assert_eq!(v, [1, 2, 3, 4]);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Self {
+        let cap = if Self::is_zst() { 0 } else { capacity };
+
+        Self {
+            ptr: unsafe { Unique::new_unchecked(ptr) },
+            cap,
+            len: length,
+            _p: PhantomData::<A>,
+        }
+    }
+
+    /// Decomposes a `Vec<T, A>` into its raw components: (`pointer`, `length`, `capacity`).
+    pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
+        let me = ManuallyDrop::new(self);
+        let len = me.len();
+        let capacity = me.capacity();
+        let ptr = me.as_mut_ptr();
+        (ptr, len, capacity)
+    }
+
+    /// Ensures that the capacity exceeds the length by at least `additional` elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = KVec::new();
+    /// v.push(1, GFP_KERNEL)?;
+    ///
+    /// v.reserve(10, GFP_KERNEL)?;
+    /// let cap = v.capacity();
+    /// assert!(cap >= 10);
+    ///
+    /// v.reserve(10, GFP_KERNEL)?;
+    /// let new_cap = v.capacity();
+    /// assert_eq!(new_cap, cap);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn reserve(&mut self, additional: usize, flags: Flags) -> Result<(), AllocError> {
+        let len = self.len();
+        let cap = self.capacity();
+
+        if cap - len >= additional {
+            return Ok(());
+        }
+
+        if Self::is_zst() {
+            // The capacity is already `usize::MAX` for SZTs, we can't go higher.
+            return Err(AllocError);
+        }
+
+        // We know cap is <= `isize::MAX` because `Layout::array` fails if the resulting byte size
+        // is greater than `isize::MAX`. So the multiplication by two won't overflow.
+        let new_cap = core::cmp::max(cap * 2, len.checked_add(additional).ok_or(AllocError)?);
+        let layout = core::alloc::Layout::array::<T>(new_cap).map_err(|_| AllocError)?;
+
+        // We need to make sure that `ptr` is either NULL or comes from a previous call to
+        // `realloc_flags`. A `Vec<T, A>`'s `ptr` value is not guaranteed to be NULL and might be
+        // dangling after being created with `Vec::new`. Instead, we can rely on `Vec<T, A>`'s
+        // capacity to be zero if no memory has been allocated yet.
+        let ptr = if cap == 0 {
+            None
+        } else {
+            Some(self.ptr.as_non_null().cast())
+        };
+
+        // SAFETY: `ptr` is valid because it's either `None` or comes from a previous call to
+        // `A::realloc`. We also verified that the type is not a ZST.
+        let ptr = unsafe { A::realloc(ptr, layout, flags)? };
+
+        self.ptr = ptr.cast().into();
+        self.cap = new_cap;
+
+        Ok(())
+    }
+}
+
+impl<T: Clone, A: Allocator> Vec<T, A> {
+    /// Extend the vector by `n` clones of value.
+    pub fn extend_with(&mut self, n: usize, value: T, flags: Flags) -> Result<(), AllocError> {
+        self.reserve(n, flags)?;
+
+        unsafe {
+            let mut ptr = self.as_mut_ptr().add(self.len());
+
+            // Write all elements except the last one
+            for _ in 1..n {
+                ptr::write(ptr, value.clone());
+                ptr = ptr.add(1);
+            }
+
+            if n > 0 {
+                // We can write the last element directly without cloning needlessly
+                ptr::write(ptr, value);
+            }
+        }
+
+        // SAFETY: `self.reserve` not bailing out with an error guarantees that we're not
+        // exceeding the capacity of this `Vec`.
+        unsafe { self.set_len(self.len() + n) };
+
+        Ok(())
+    }
+
+    /// Create a new `Vec<T, A> and extend it by `n` clones of value.
+    pub fn from_elem(value: T, n: usize, flags: Flags) -> Result<Self, AllocError> {
+        let mut v = Self::with_capacity(n, flags)?;
+
+        v.extend_with(n, value, flags)?;
+
+        Ok(v)
+    }
+}
+
+impl<T, A> Drop for Vec<T, A>
+where
+    A: Allocator,
+{
+    fn drop(&mut self) {
+        // SAFETY: We need to drop the vector's elements in place, before we free the backing
+        // memory.
+        unsafe {
+            core::ptr::drop_in_place(core::ptr::slice_from_raw_parts_mut(
+                self.as_mut_ptr(),
+                self.len,
+            ))
+        };
+
+        // If `cap == 0` we never allocated any memory in the first place.
+        if self.cap != 0 {
+            // SAFETY: `self.ptr` was previously allocated with `A`.
+            unsafe { A::free(self.ptr.as_non_null().cast()) };
+        }
+    }
+}
+
+impl<T> Default for KVec<T> {
+    #[inline]
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T: fmt::Debug, A: Allocator> fmt::Debug for Vec<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T, A> Deref for Vec<T, A>
+where
+    A: Allocator,
+{
+    type Target = [T];
+
+    #[inline]
+    fn deref(&self) -> &[T] {
+        unsafe { slice::from_raw_parts(self.as_ptr(), self.len) }
+    }
+}
+
+impl<T, A> DerefMut for Vec<T, A>
+where
+    A: Allocator,
+{
+    #[inline]
+    fn deref_mut(&mut self) -> &mut [T] {
+        unsafe { slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) }
+    }
+}
+
+impl<T: Eq, A> Eq for Vec<T, A> where A: Allocator {}
+
+impl<T, I: SliceIndex<[T]>, A> Index<I> for Vec<T, A>
+where
+    A: Allocator,
+{
+    type Output = I::Output;
+
+    #[inline]
+    fn index(&self, index: I) -> &Self::Output {
+        Index::index(&**self, index)
+    }
+}
+
+impl<T, I: SliceIndex<[T]>, A> IndexMut<I> for Vec<T, A>
+where
+    A: Allocator,
+{
+    #[inline]
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+
+macro_rules! __impl_slice_eq {
+    ([$($vars:tt)*] $lhs:ty, $rhs:ty $(where $ty:ty: $bound:ident)?) => {
+        impl<T, U, $($vars)*> PartialEq<$rhs> for $lhs
+        where
+            T: PartialEq<U>,
+            $($ty: $bound)?
+        {
+            #[inline]
+            fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
+        }
+    }
+}
+
+__impl_slice_eq! { [A1: Allocator, A2: Allocator] Vec<T, A1>, Vec<U, A2> }
+__impl_slice_eq! { [A: Allocator] Vec<T, A>, &[U] }
+__impl_slice_eq! { [A: Allocator] Vec<T, A>, &mut [U] }
+__impl_slice_eq! { [A: Allocator] &[T], Vec<U, A> }
+__impl_slice_eq! { [A: Allocator] &mut [T], Vec<U, A> }
+__impl_slice_eq! { [A: Allocator] Vec<T, A>, [U] }
+__impl_slice_eq! { [A: Allocator] [T], Vec<U, A> }
+__impl_slice_eq! { [A: Allocator, const N: usize] Vec<T, A>, [U; N] }
+__impl_slice_eq! { [A: Allocator, const N: usize] Vec<T, A>, &[U; N] }
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 6bf77577eae7..bb80a43d20fb 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,7 +14,7 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{flags::*, vec_ext::VecExt, Box, KBox, KVBox, VBox};
+pub use crate::alloc::{flags::*, vec_ext::VecExt, Box, KBox, KVBox, KVVec, KVec, VBox, VVec};
 
 #[doc(no_inline)]
 pub use alloc::vec::Vec;
-- 
2.45.2

[PATCH v2 15/23] rust: alloc: implement `IntoIterator` for `Vec`

[Danilo Krummrich]

Implement `IntoIterator` for `Vec`, `Vec`'s `IntoIter` type, as well as
`Iterator` for `IntoIter`.

`Vec::into_iter` disassembles the `Vec` into its raw parts; additionally,
`IntoIter` keeps track of a separate pointer, which is incremented
correspondingsly as the iterator advances, while the length, or the count
of elements, is decremented.

This also means that `IntoIter` takes the ownership of the backing
buffer and is responsible to drop the remaining elements and free the
backing buffer, if it's dropped.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs      |   1 +
 rust/kernel/alloc/kvec.rs | 175 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 175 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 827922e1f1d1..19e0ad0bf98b 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -19,6 +19,7 @@
 pub use self::kbox::KVBox;
 pub use self::kbox::VBox;
 
+pub use self::kvec::IntoIter;
 pub use self::kvec::KVVec;
 pub use self::kvec::KVec;
 pub use self::kvec::VVec;
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 58b3f679ad83..fbfb755b252d 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -12,7 +12,9 @@
     ops::DerefMut,
     ops::Index,
     ops::IndexMut,
-    ptr, slice,
+    ptr,
+    ptr::NonNull,
+    slice,
     slice::SliceIndex,
 };
 
@@ -578,3 +580,174 @@ fn eq(&self, other: &$rhs) -> bool { self[..] == other[..] }
 __impl_slice_eq! { [A: Allocator] [T], Vec<U, A> }
 __impl_slice_eq! { [A: Allocator, const N: usize] Vec<T, A>, [U; N] }
 __impl_slice_eq! { [A: Allocator, const N: usize] Vec<T, A>, &[U; N] }
+
+impl<'a, T, A> IntoIterator for &'a Vec<T, A>
+where
+    A: Allocator,
+{
+    type Item = &'a T;
+    type IntoIter = slice::Iter<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, T, A: Allocator> IntoIterator for &'a mut Vec<T, A>
+where
+    A: Allocator,
+{
+    type Item = &'a mut T;
+    type IntoIter = slice::IterMut<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+/// An iterator that moves out of a vector.
+///
+/// This `struct` is created by the `into_iter` method on [`Vec`] (provided by the [`IntoIterator`]
+/// trait).
+///
+/// # Examples
+///
+/// ```
+/// let v = kernel::kvec![0, 1, 2]?;
+/// let iter = v.into_iter();
+///
+/// # Ok::<(), Error>(())
+/// ```
+pub struct IntoIter<T, A: Allocator> {
+    ptr: *mut T,
+    buf: NonNull<T>,
+    len: usize,
+    cap: usize,
+    _p: PhantomData<A>,
+}
+
+impl<T, A> IntoIter<T, A>
+where
+    A: Allocator,
+{
+    fn as_raw_mut_slice(&mut self) -> *mut [T] {
+        ptr::slice_from_raw_parts_mut(self.ptr, self.len)
+    }
+}
+
+impl<T, A> Iterator for IntoIter<T, A>
+where
+    A: Allocator,
+{
+    type Item = T;
+
+    /// # Examples
+    ///
+    /// ```
+    /// let v = kernel::kvec![1, 2, 3]?;
+    /// let mut it = v.into_iter();
+    ///
+    /// assert_eq!(it.next(), Some(1));
+    /// assert_eq!(it.next(), Some(2));
+    /// assert_eq!(it.next(), Some(3));
+    /// assert_eq!(it.next(), None);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    fn next(&mut self) -> Option<T> {
+        if self.len == 0 {
+            return None;
+        }
+
+        let ptr = self.ptr;
+        if !Vec::<T, A>::is_zst() {
+            // SAFETY: We can't overflow; `end` is guaranteed to mark the end of the buffer.
+            unsafe { self.ptr = self.ptr.add(1) };
+        } else {
+            // For ZST `ptr` has to stay where it is to remain aligned, so we just reduce `self.len`
+            // by 1.
+        }
+        self.len -= 1;
+
+        // SAFETY: `ptr` is guaranteed to point at a valid element within the buffer.
+        Some(unsafe { ptr.read() })
+    }
+
+    /// # Examples
+    ///
+    /// ```
+    /// let v: KVec<u32> = kernel::kvec![1, 2, 3]?;
+    /// let mut iter = v.into_iter();
+    /// let size = iter.size_hint().0;
+    ///
+    /// iter.next();
+    /// assert_eq!(iter.size_hint().0, size - 1);
+    ///
+    /// iter.next();
+    /// assert_eq!(iter.size_hint().0, size - 2);
+    ///
+    /// iter.next();
+    /// assert_eq!(iter.size_hint().0, size - 3);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len, Some(self.len))
+    }
+}
+
+impl<T, A> Drop for IntoIter<T, A>
+where
+    A: Allocator,
+{
+    fn drop(&mut self) {
+        // SAFETY: Drop the remaining vector's elements in place, before we free the backing
+        // memory.
+        unsafe { ptr::drop_in_place(self.as_raw_mut_slice()) };
+
+        // If `cap == 0` we never allocated any memory in the first place.
+        if self.cap != 0 {
+            // SAFETY: `self.buf` was previously allocated with `A`.
+            unsafe { A::free(self.buf.cast()) };
+        }
+    }
+}
+
+impl<T, A> IntoIterator for Vec<T, A>
+where
+    A: Allocator,
+{
+    type Item = T;
+    type IntoIter = IntoIter<T, A>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out of
+    /// the vector (from start to end). The vector cannot be used after calling
+    /// this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = kernel::kvec![1, 2]?;
+    /// let mut v_iter = v.into_iter();
+    ///
+    /// let first_element: Option<u32> = v_iter.next();
+    ///
+    /// assert_eq!(first_element, Some(1));
+    /// assert_eq!(v_iter.next(), Some(2));
+    /// assert_eq!(v_iter.next(), None);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        let (ptr, len, cap) = self.into_raw_parts();
+
+        IntoIter {
+            ptr,
+            buf: unsafe { NonNull::new_unchecked(ptr) },
+            len,
+            cap,
+            _p: PhantomData::<A>,
+        }
+    }
+}
-- 
2.45.2

[PATCH v2 16/23] rust: alloc: implement `collect` for `IntoIter`

[Danilo Krummrich]

Currently, we can't implement `FromIterator`. There are a couple of
issues with this trait in the kernel, namely:

  - Rust's specialization feature is unstable. This prevents us to
    optimze for the special case where `I::IntoIter` equals `Vec`'s
    `IntoIter` type.
  - We also can't use `I::IntoIter`'s type ID either to work around this,
    since `FromIterator` doesn't require this type to be `'static`.
  - `FromIterator::from_iter` does return `Self` instead of
    `Result<Self, AllocError>`, hence we can't properly handle allocation
    failures.
  - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle
    additional allocation flags.

Instead, provide `IntoIter::collect`, such that we can at least convert
`IntoIter` into a `Vec` again.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 79 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index fbfb755b252d..5c317931e14c 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -2,7 +2,7 @@
 
 //! Implementation of [`Vec`].
 
-use super::{AllocError, Allocator, Flags};
+use super::{flags::*, AllocError, Allocator, Flags};
 use crate::types::Unique;
 use core::{
     fmt,
@@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A>
     fn as_raw_mut_slice(&mut self) -> *mut [T] {
         ptr::slice_from_raw_parts_mut(self.ptr, self.len)
     }
+
+    fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) {
+        let me = ManuallyDrop::new(self);
+        let ptr = me.ptr;
+        let buf = me.buf;
+        let len = me.len;
+        let cap = me.cap;
+        (ptr, buf, len, cap)
+    }
+
+    /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`.
+    ///
+    /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait
+    /// in the kernel, namely:
+    ///
+    /// - Rust's specialization feature is unstable. This prevents us to optimze for the special
+    ///   case where `I::IntoIter` equals `Vec`'s `IntoIter` type.
+    /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator`
+    ///   doesn't require this type to be `'static`.
+    /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence
+    ///   we can't properly handle allocation failures.
+    /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation
+    ///   flags.
+    ///
+    /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a
+    /// `Vec` again.
+    ///
+    /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing
+    /// buffer. However, this backing buffer may be shrunk to the actual count of elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = kernel::kvec![1, 2, 3]?;
+    /// let mut it = v.into_iter();
+    ///
+    /// assert_eq!(it.next(), Some(1));
+    ///
+    /// let v = it.collect();
+    /// assert_eq!(v, [2, 3]);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn collect(self) -> Vec<T, A> {
+        let (mut ptr, buf, len, mut cap) = self.into_raw_parts();
+        let has_advanced = ptr != buf.as_ptr();
+
+        if has_advanced {
+            // SAFETY: Copy the contents we have advanced to at the beginning of the buffer.
+            // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is
+            // guaranteed to be smaller than `buf.add(cap)`.
+            unsafe { ptr::copy(ptr, buf.as_ptr(), len) };
+            ptr = buf.as_ptr();
+        }
+
+        // This can never fail, `len` is guaranteed to be smaller than `cap`.
+        let layout = core::alloc::Layout::array::<T>(len).unwrap();
+
+        // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be
+        // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves
+        // it as it is.
+        ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } {
+            // If we fail to shrink, which likely can't even happen, continue with the existing
+            // buffer.
+            Err(_) => ptr,
+            Ok(ptr) => {
+                cap = len;
+                ptr.as_ptr().cast()
+            }
+        };
+
+        // SAFETY: If the iterator has been advanced, the advanced elements have been copied to
+        // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed
+        // to point to the start of the backing buffer. `cap` is either the original capacity or,
+        // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since
+        // `into_iter` has been called on the original `Vec`.
+        unsafe { Vec::from_raw_parts(ptr, len, cap) }
+    }
 }
 
 impl<T, A> Iterator for IntoIter<T, A>
-- 
2.45.2

[PATCH v2 17/23] rust: treewide: switch to the kernel `Vec` type

[Danilo Krummrich]

Now that we got the kernel `Vec` in place, convert all existing `Vec`
users to make use of it.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/str.rs            | 12 +++++-------
 rust/kernel/sync/locked_by.rs |  2 +-
 rust/kernel/types.rs          |  2 +-
 samples/rust/rust_minimal.rs  |  4 ++--
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index bb8d4f41475b..0b6ffbade521 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -2,8 +2,7 @@
 
 //! String representations.
 
-use crate::alloc::{flags::*, vec_ext::VecExt, AllocError};
-use alloc::vec::Vec;
+use crate::alloc::{flags::*, AllocError, KVec};
 use core::fmt::{self, Write};
 use core::ops::{self, Deref, DerefMut, Index};
 
@@ -790,7 +789,7 @@ fn write_str(&mut self, s: &str) -> fmt::Result {
 /// assert_eq!(s.is_ok(), false);
 /// ```
 pub struct CString {
-    buf: Vec<u8>,
+    buf: KVec<u8>,
 }
 
 impl CString {
@@ -803,7 +802,7 @@ pub fn try_from_fmt(args: fmt::Arguments<'_>) -> Result<Self, Error> {
         let size = f.bytes_written();
 
         // Allocate a vector with the required number of bytes, and write to it.
-        let mut buf = <Vec<_> as VecExt<_>>::with_capacity(size, GFP_KERNEL)?;
+        let mut buf = KVec::with_capacity(size, GFP_KERNEL)?;
         // SAFETY: The buffer stored in `buf` is at least of size `size` and is valid for writes.
         let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
         f.write_fmt(args)?;
@@ -850,10 +849,9 @@ impl<'a> TryFrom<&'a CStr> for CString {
     type Error = AllocError;
 
     fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
-        let mut buf = Vec::new();
+        let mut buf = KVec::new();
 
-        <Vec<_> as VecExt<_>>::extend_from_slice(&mut buf, cstr.as_bytes_with_nul(), GFP_KERNEL)
-            .map_err(|_| AllocError)?;
+        KVec::extend_from_slice(&mut buf, cstr.as_bytes_with_nul(), GFP_KERNEL)?;
 
         // INVARIANT: The `CStr` and `CString` types have the same invariants for
         // the string data, and we copied it over without changes.
diff --git a/rust/kernel/sync/locked_by.rs b/rust/kernel/sync/locked_by.rs
index babc731bd5f6..b94517231fcc 100644
--- a/rust/kernel/sync/locked_by.rs
+++ b/rust/kernel/sync/locked_by.rs
@@ -43,7 +43,7 @@
 /// struct InnerDirectory {
 ///     /// The sum of the bytes used by all files.
 ///     bytes_used: u64,
-///     _files: Vec<File>,
+///     _files: KVec<File>,
 /// }
 ///
 /// struct Directory {
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index ee0063a20d89..05521403ed2c 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -158,7 +158,7 @@ unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
 /// # use kernel::types::ScopeGuard;
 /// fn example3(arg: bool) -> Result {
 ///     let mut vec =
-///         ScopeGuard::new_with_data(Vec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
+///         ScopeGuard::new_with_data(KVec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
 ///
 ///     vec.push(10u8, GFP_KERNEL)?;
 ///     if arg {
diff --git a/samples/rust/rust_minimal.rs b/samples/rust/rust_minimal.rs
index 2a9eaab62d1c..4aaf117bf8e3 100644
--- a/samples/rust/rust_minimal.rs
+++ b/samples/rust/rust_minimal.rs
@@ -13,7 +13,7 @@
 }
 
 struct RustMinimal {
-    numbers: Vec<i32>,
+    numbers: KVec<i32>,
 }
 
 impl kernel::Module for RustMinimal {
@@ -21,7 +21,7 @@ fn init(_module: &'static ThisModule) -> Result<Self> {
         pr_info!("Rust minimal sample (init)\n");
         pr_info!("Am I built-in? {}\n", !cfg!(MODULE));
 
-        let mut numbers = Vec::new();
+        let mut numbers = KVec::new();
         numbers.push(72, GFP_KERNEL)?;
         numbers.push(108, GFP_KERNEL)?;
         numbers.push(200, GFP_KERNEL)?;
-- 
2.45.2

[PATCH v2 18/23] rust: alloc: remove `VecExt` extension

[Danilo Krummrich]

Now that all existing `Vec` users were moved to the kernel `Vec` type,
remove the `VecExt` extension.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc.rs         |   1 -
 rust/kernel/alloc/vec_ext.rs | 185 -----------------------------------
 rust/kernel/prelude.rs       |   5 +-
 3 files changed, 1 insertion(+), 190 deletions(-)
 delete mode 100644 rust/kernel/alloc/vec_ext.rs

diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index 19e0ad0bf98b..62838738f409 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -6,7 +6,6 @@
 pub mod allocator;
 pub mod kbox;
 pub mod kvec;
-pub mod vec_ext;
 
 #[cfg(any(test, testlib))]
 pub mod allocator_test;
diff --git a/rust/kernel/alloc/vec_ext.rs b/rust/kernel/alloc/vec_ext.rs
deleted file mode 100644
index 1297a4be32e8..000000000000
--- a/rust/kernel/alloc/vec_ext.rs
+++ /dev/null
@@ -1,185 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-
-//! Extensions to [`Vec`] for fallible allocations.
-
-use super::{AllocError, Flags};
-use alloc::vec::Vec;
-
-/// Extensions to [`Vec`].
-pub trait VecExt<T>: Sized {
-    /// Creates a new [`Vec`] instance with at least the given capacity.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let v = Vec::<u32>::with_capacity(20, GFP_KERNEL)?;
-    ///
-    /// assert!(v.capacity() >= 20);
-    /// # Ok::<(), Error>(())
-    /// ```
-    fn with_capacity(capacity: usize, flags: Flags) -> Result<Self, AllocError>;
-
-    /// Appends an element to the back of the [`Vec`] instance.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let mut v = Vec::new();
-    /// v.push(1, GFP_KERNEL)?;
-    /// assert_eq!(&v, &[1]);
-    ///
-    /// v.push(2, GFP_KERNEL)?;
-    /// assert_eq!(&v, &[1, 2]);
-    /// # Ok::<(), Error>(())
-    /// ```
-    fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError>;
-
-    /// Pushes clones of the elements of slice into the [`Vec`] instance.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let mut v = Vec::new();
-    /// v.push(1, GFP_KERNEL)?;
-    ///
-    /// v.extend_from_slice(&[20, 30, 40], GFP_KERNEL)?;
-    /// assert_eq!(&v, &[1, 20, 30, 40]);
-    ///
-    /// v.extend_from_slice(&[50, 60], GFP_KERNEL)?;
-    /// assert_eq!(&v, &[1, 20, 30, 40, 50, 60]);
-    /// # Ok::<(), Error>(())
-    /// ```
-    fn extend_from_slice(&mut self, other: &[T], flags: Flags) -> Result<(), AllocError>
-    where
-        T: Clone;
-
-    /// Ensures that the capacity exceeds the length by at least `additional` elements.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// let mut v = Vec::new();
-    /// v.push(1, GFP_KERNEL)?;
-    ///
-    /// v.reserve(10, GFP_KERNEL)?;
-    /// let cap = v.capacity();
-    /// assert!(cap >= 10);
-    ///
-    /// v.reserve(10, GFP_KERNEL)?;
-    /// let new_cap = v.capacity();
-    /// assert_eq!(new_cap, cap);
-    ///
-    /// # Ok::<(), Error>(())
-    /// ```
-    fn reserve(&mut self, additional: usize, flags: Flags) -> Result<(), AllocError>;
-}
-
-impl<T> VecExt<T> for Vec<T> {
-    fn with_capacity(capacity: usize, flags: Flags) -> Result<Self, AllocError> {
-        let mut v = Vec::new();
-        <Self as VecExt<_>>::reserve(&mut v, capacity, flags)?;
-        Ok(v)
-    }
-
-    fn push(&mut self, v: T, flags: Flags) -> Result<(), AllocError> {
-        <Self as VecExt<_>>::reserve(self, 1, flags)?;
-        let s = self.spare_capacity_mut();
-        s[0].write(v);
-
-        // SAFETY: We just initialised the first spare entry, so it is safe to increase the length
-        // by 1. We also know that the new length is <= capacity because of the previous call to
-        // `reserve` above.
-        unsafe { self.set_len(self.len() + 1) };
-        Ok(())
-    }
-
-    fn extend_from_slice(&mut self, other: &[T], flags: Flags) -> Result<(), AllocError>
-    where
-        T: Clone,
-    {
-        <Self as VecExt<_>>::reserve(self, other.len(), flags)?;
-        for (slot, item) in core::iter::zip(self.spare_capacity_mut(), other) {
-            slot.write(item.clone());
-        }
-
-        // SAFETY: We just initialised the `other.len()` spare entries, so it is safe to increase
-        // the length by the same amount. We also know that the new length is <= capacity because
-        // of the previous call to `reserve` above.
-        unsafe { self.set_len(self.len() + other.len()) };
-        Ok(())
-    }
-
-    #[cfg(any(test, testlib))]
-    fn reserve(&mut self, additional: usize, _flags: Flags) -> Result<(), AllocError> {
-        Vec::reserve(self, additional);
-        Ok(())
-    }
-
-    #[cfg(not(any(test, testlib)))]
-    fn reserve(&mut self, additional: usize, flags: Flags) -> Result<(), AllocError> {
-        let len = self.len();
-        let cap = self.capacity();
-
-        if cap - len >= additional {
-            return Ok(());
-        }
-
-        if core::mem::size_of::<T>() == 0 {
-            // The capacity is already `usize::MAX` for SZTs, we can't go higher.
-            return Err(AllocError);
-        }
-
-        // We know cap is <= `isize::MAX` because `Layout::array` fails if the resulting byte size
-        // is greater than `isize::MAX`. So the multiplication by two won't overflow.
-        let new_cap = core::cmp::max(cap * 2, len.checked_add(additional).ok_or(AllocError)?);
-        let layout = core::alloc::Layout::array::<T>(new_cap).map_err(|_| AllocError)?;
-
-        let (old_ptr, len, cap) = destructure(self);
-
-        // We need to make sure that `ptr` is either NULL or comes from a previous call to
-        // `krealloc_aligned`. A `Vec<T>`'s `ptr` value is not guaranteed to be NULL and might be
-        // dangling after being created with `Vec::new`. Instead, we can rely on `Vec<T>`'s capacity
-        // to be zero if no memory has been allocated yet.
-        let ptr = if cap == 0 {
-            core::ptr::null_mut()
-        } else {
-            old_ptr
-        };
-
-        // SAFETY: `ptr` is valid because it's either NULL or comes from a previous call to
-        // `krealloc_aligned`. We also verified that the type is not a ZST.
-        let new_ptr = unsafe { super::allocator::krealloc_aligned(ptr.cast(), layout, flags) };
-        if new_ptr.is_null() {
-            // SAFETY: We are just rebuilding the existing `Vec` with no changes.
-            unsafe { rebuild(self, old_ptr, len, cap) };
-            Err(AllocError)
-        } else {
-            // SAFETY: `ptr` has been reallocated with the layout for `new_cap` elements. New cap
-            // is greater than `cap`, so it continues to be >= `len`.
-            unsafe { rebuild(self, new_ptr.cast::<T>(), len, new_cap) };
-            Ok(())
-        }
-    }
-}
-
-#[cfg(not(any(test, testlib)))]
-fn destructure<T>(v: &mut Vec<T>) -> (*mut T, usize, usize) {
-    let mut tmp = Vec::new();
-    core::mem::swap(&mut tmp, v);
-    let mut tmp = core::mem::ManuallyDrop::new(tmp);
-    let len = tmp.len();
-    let cap = tmp.capacity();
-    (tmp.as_mut_ptr(), len, cap)
-}
-
-/// Rebuilds a `Vec` from a pointer, length, and capacity.
-///
-/// # Safety
-///
-/// The same as [`Vec::from_raw_parts`].
-#[cfg(not(any(test, testlib)))]
-unsafe fn rebuild<T>(v: &mut Vec<T>, ptr: *mut T, len: usize, cap: usize) {
-    // SAFETY: The safety requirements from this function satisfy those of `from_raw_parts`.
-    let mut tmp = unsafe { Vec::from_raw_parts(ptr, len, cap) };
-    core::mem::swap(&mut tmp, v);
-}
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index bb80a43d20fb..fcc8656fdb51 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,10 +14,7 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{flags::*, vec_ext::VecExt, Box, KBox, KVBox, KVVec, KVec, VBox, VVec};
-
-#[doc(no_inline)]
-pub use alloc::vec::Vec;
+pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec};
 
 #[doc(no_inline)]
 pub use macros::{module, pin_data, pinned_drop, vtable, Zeroable};
-- 
2.45.2

[PATCH v2 19/23] rust: alloc: add `Vec` to prelude

[Danilo Krummrich]

Now that we removed `VecExt` and the corresponding includes in
prelude.rs, add the new kernel `Vec` type instead.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/prelude.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index fcc8656fdb51..b049ab96202e 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -14,7 +14,7 @@
 #[doc(no_inline)]
 pub use core::pin::Pin;
 
-pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec};
+pub use crate::alloc::{flags::*, Box, KBox, KVBox, KVVec, KVec, VBox, VVec, Vec};
 
 #[doc(no_inline)]
 pub use macros::{module, pin_data, pinned_drop, vtable, Zeroable};
-- 
2.45.2

[PATCH v2 20/23] rust: alloc: remove `GlobalAlloc` and `krealloc_aligned`

[Danilo Krummrich]

Now that we have all the `Allocator`s and the kernel `Box` and `Vec`
implementations in place, remove `GlobalAlloc` and `krealloc_aligned`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/alloc/allocator.rs | 63 ++--------------------------------
 1 file changed, 2 insertions(+), 61 deletions(-)

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 1e53f149db96..fbee89ac3be4 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -2,8 +2,8 @@
 
 //! Allocator support.
 
-use super::{flags::*, Flags};
-use core::alloc::{GlobalAlloc, Layout};
+use super::Flags;
+use core::alloc::Layout;
 use core::ptr;
 use core::ptr::NonNull;
 
@@ -39,27 +39,6 @@ fn aligned_size(new_layout: Layout) -> usize {
     layout.size()
 }
 
-/// Calls `krealloc` with a proper size to alloc a new object.
-///
-/// # Safety
-///
-/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
-/// - `new_layout` must have a non-zero size.
-pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
-    // SAFETY:
-    // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
-    //   function safety requirement.
-    // - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
-    //   to the function safety requirement)
-    unsafe {
-        bindings::krealloc(
-            ptr as *const core::ffi::c_void,
-            aligned_size(new_layout),
-            flags.0,
-        ) as *mut u8
-    }
-}
-
 struct ReallocFunc(
     // INVARIANT: One of the following `krealloc`, `vrealloc`, `kvrealloc`.
     unsafe extern "C" fn(*const core::ffi::c_void, usize, u32) -> *mut core::ffi::c_void,
@@ -121,41 +100,6 @@ unsafe fn realloc(
     }
 }
 
-unsafe impl GlobalAlloc for Kmalloc {
-    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
-        // requirement.
-        unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL) }
-    }
-
-    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
-        unsafe {
-            bindings::kfree(ptr as *const core::ffi::c_void);
-        }
-    }
-
-    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
-        // SAFETY:
-        // - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
-        //   overflow `isize` by the function safety requirement.
-        // - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
-        let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
-
-        // SAFETY:
-        // - `ptr` is either null or a pointer allocated by this allocator by the function safety
-        //   requirement.
-        // - the size of `layout` is not zero because `new_size` is not zero by the function safety
-        //   requirement.
-        unsafe { krealloc_aligned(ptr, layout, GFP_KERNEL) }
-    }
-
-    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
-        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
-        // requirement.
-        unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL | __GFP_ZERO) }
-    }
-}
-
 unsafe impl Allocator for Vmalloc {
     unsafe fn realloc(
         ptr: Option<NonNull<u8>>,
@@ -184,9 +128,6 @@ unsafe fn realloc(
     }
 }
 
-#[global_allocator]
-static ALLOCATOR: Kmalloc = Kmalloc;
-
 // See <https://github.com/rust-lang/rust/pull/86844>.
 #[no_mangle]
 static __rust_no_alloc_shim_is_unstable: u8 = 0;
-- 
2.45.2

[PATCH v2 21/23] rust: error: use `core::alloc::LayoutError`

[Danilo Krummrich]

Use `core::alloc::LayoutError` instead of `alloc::alloc::LayoutError` in
preparation to get rid of Rust's alloc crate.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/error.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
index 145f5c397009..2d012cc3881a 100644
--- a/rust/kernel/error.rs
+++ b/rust/kernel/error.rs
@@ -6,7 +6,7 @@
 
 use crate::{alloc::AllocError, str::CStr};
 
-use alloc::alloc::LayoutError;
+use core::alloc::LayoutError;
 
 use core::fmt;
 use core::num::TryFromIntError;
-- 
2.45.2

[PATCH v2 22/23] rust: str: test: replace `alloc::format`

[Danilo Krummrich]

The current implementation of tests in str.rs use `format!` to format
strings for comparison, which, internally, creates a new `String`.

In order to prepare for getting rid of Rust's alloc crate, we have to
cut this dependency. Instead, we could implement `format!` for
`CString`, however `CString` uses the kernel `Vec` type and hence the
kernel allocators, which can't be used for tests run in userspace.

Instead, implement `fmt_assert_eq`, which formats strings into a stack
allocated buffer for comparison with a `&str`.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/str.rs | 66 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 46 insertions(+), 20 deletions(-)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 0b6ffbade521..539be40754f4 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -523,7 +523,6 @@ macro_rules! c_str {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use alloc::format;
 
     const ALL_ASCII_CHARS: &'static str =
         "\\x01\\x02\\x03\\x04\\x05\\x06\\x07\\x08\\x09\\x0a\\x0b\\x0c\\x0d\\x0e\\x0f\
@@ -539,6 +538,33 @@ mod tests {
         \\xe0\\xe1\\xe2\\xe3\\xe4\\xe5\\xe6\\xe7\\xe8\\xe9\\xea\\xeb\\xec\\xed\\xee\\xef\
         \\xf0\\xf1\\xf2\\xf3\\xf4\\xf5\\xf6\\xf7\\xf8\\xf9\\xfa\\xfb\\xfc\\xfd\\xfe\\xff";
 
+    fn format_into_buf<'a>(args: fmt::Arguments<'_>, buf: &'a mut [u8]) -> Result<&'a str, Error> {
+        let mut f = RawFormatter::new();
+        f.write_fmt(args)?;
+        let size = f.bytes_written();
+
+        assert!(buf.len() >= size);
+
+        // SAFETY: `buf` has at least a size of `size` bytes and is valid for writes.
+        let mut f = unsafe { Formatter::from_buffer(buf.as_mut_ptr(), size) };
+        f.write_fmt(args)?;
+
+        Ok(core::str::from_utf8(&buf[0..size])?)
+    }
+
+    macro_rules! fmt_assert_eq {
+        ($str:expr, $($f:tt)*) => ({
+            let mut buf = [0_u8; ALL_ASCII_CHARS.len()];
+
+            let s = match format_into_buf(kernel::fmt!($($f)*), &mut buf) {
+                Ok(s) => s,
+                Err(_) => panic!("Could not format into buffer."),
+            };
+
+            assert_eq!($str, s);
+        })
+    }
+
     #[test]
     fn test_cstr_to_str() {
         let good_bytes = b"\xf0\x9f\xa6\x80\0";
@@ -566,13 +592,13 @@ fn test_cstr_as_str_unchecked() {
     #[test]
     fn test_cstr_display() {
         let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0").unwrap();
-        assert_eq!(format!("{}", hello_world), "hello, world!");
+        fmt_assert_eq!("hello, world!", "{}", hello_world);
         let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0").unwrap();
-        assert_eq!(format!("{}", non_printables), "\\x01\\x09\\x0a");
+        fmt_assert_eq!("\\x01\\x09\\x0a", "{}", non_printables);
         let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0").unwrap();
-        assert_eq!(format!("{}", non_ascii), "d\\xe9j\\xe0 vu");
+        fmt_assert_eq!("d\\xe9j\\xe0 vu", "{}", non_ascii);
         let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0").unwrap();
-        assert_eq!(format!("{}", good_bytes), "\\xf0\\x9f\\xa6\\x80");
+        fmt_assert_eq!("\\xf0\\x9f\\xa6\\x80", "{}", good_bytes);
     }
 
     #[test]
@@ -583,47 +609,47 @@ fn test_cstr_display_all_bytes() {
             bytes[i as usize] = i.wrapping_add(1);
         }
         let cstr = CStr::from_bytes_with_nul(&bytes).unwrap();
-        assert_eq!(format!("{}", cstr), ALL_ASCII_CHARS);
+        fmt_assert_eq!(ALL_ASCII_CHARS, "{}", cstr);
     }
 
     #[test]
     fn test_cstr_debug() {
         let hello_world = CStr::from_bytes_with_nul(b"hello, world!\0").unwrap();
-        assert_eq!(format!("{:?}", hello_world), "\"hello, world!\"");
+        fmt_assert_eq!("\"hello, world!\"", "{:?}", hello_world);
         let non_printables = CStr::from_bytes_with_nul(b"\x01\x09\x0a\0").unwrap();
-        assert_eq!(format!("{:?}", non_printables), "\"\\x01\\x09\\x0a\"");
+        fmt_assert_eq!("\"\\x01\\x09\\x0a\"", "{:?}", non_printables);
         let non_ascii = CStr::from_bytes_with_nul(b"d\xe9j\xe0 vu\0").unwrap();
-        assert_eq!(format!("{:?}", non_ascii), "\"d\\xe9j\\xe0 vu\"");
+        fmt_assert_eq!("\"d\\xe9j\\xe0 vu\"", "{:?}", non_ascii);
         let good_bytes = CStr::from_bytes_with_nul(b"\xf0\x9f\xa6\x80\0").unwrap();
-        assert_eq!(format!("{:?}", good_bytes), "\"\\xf0\\x9f\\xa6\\x80\"");
+        fmt_assert_eq!("\"\\xf0\\x9f\\xa6\\x80\"", "{:?}", good_bytes);
     }
 
     #[test]
     fn test_bstr_display() {
         let hello_world = BStr::from_bytes(b"hello, world!");
-        assert_eq!(format!("{}", hello_world), "hello, world!");
+        fmt_assert_eq!("hello, world!", "{}", hello_world);
         let escapes = BStr::from_bytes(b"_\t_\n_\r_\\_\'_\"_");
-        assert_eq!(format!("{}", escapes), "_\\t_\\n_\\r_\\_'_\"_");
+        fmt_assert_eq!("_\\t_\\n_\\r_\\_'_\"_", "{}", escapes);
         let others = BStr::from_bytes(b"\x01");
-        assert_eq!(format!("{}", others), "\\x01");
+        fmt_assert_eq!("\\x01", "{}", others);
         let non_ascii = BStr::from_bytes(b"d\xe9j\xe0 vu");
-        assert_eq!(format!("{}", non_ascii), "d\\xe9j\\xe0 vu");
+        fmt_assert_eq!("d\\xe9j\\xe0 vu", "{}", non_ascii);
         let good_bytes = BStr::from_bytes(b"\xf0\x9f\xa6\x80");
-        assert_eq!(format!("{}", good_bytes), "\\xf0\\x9f\\xa6\\x80");
+        fmt_assert_eq!("\\xf0\\x9f\\xa6\\x80", "{}", good_bytes);
     }
 
     #[test]
     fn test_bstr_debug() {
         let hello_world = BStr::from_bytes(b"hello, world!");
-        assert_eq!(format!("{:?}", hello_world), "\"hello, world!\"");
+        fmt_assert_eq!("\"hello, world!\"", "{:?}", hello_world);
         let escapes = BStr::from_bytes(b"_\t_\n_\r_\\_\'_\"_");
-        assert_eq!(format!("{:?}", escapes), "\"_\\t_\\n_\\r_\\\\_'_\\\"_\"");
+        fmt_assert_eq!("\"_\\t_\\n_\\r_\\\\_'_\\\"_\"", "{:?}", escapes);
         let others = BStr::from_bytes(b"\x01");
-        assert_eq!(format!("{:?}", others), "\"\\x01\"");
+        fmt_assert_eq!("\"\\x01\"", "{:?}", others);
         let non_ascii = BStr::from_bytes(b"d\xe9j\xe0 vu");
-        assert_eq!(format!("{:?}", non_ascii), "\"d\\xe9j\\xe0 vu\"");
+        fmt_assert_eq!("\"d\\xe9j\\xe0 vu\"", "{:?}", non_ascii);
         let good_bytes = BStr::from_bytes(b"\xf0\x9f\xa6\x80");
-        assert_eq!(format!("{:?}", good_bytes), "\"\\xf0\\x9f\\xa6\\x80\"");
+        fmt_assert_eq!("\"\\xf0\\x9f\\xa6\\x80\"", "{:?}", good_bytes);
     }
 }
 
-- 
2.45.2

[PATCH v2 23/23] kbuild: rust: remove the `alloc` crate

[Danilo Krummrich]

Now that we have our own `Allocator`, `Box` and `Vec` types we can remove
Rust's `alloc` crate and the corresponding unstable features.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/Makefile          | 44 ++++++++++--------------------------------
 rust/exports.c         |  1 -
 scripts/Makefile.build |  7 +------
 3 files changed, 11 insertions(+), 41 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index f70d5e244fee..409be08ad09a 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -15,9 +15,8 @@ always-$(CONFIG_RUST) += libmacros.so
 no-clean-files += libmacros.so
 
 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
-obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
-always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
-    exports_kernel_generated.h
+obj-$(CONFIG_RUST) += bindings.o kernel.o
+always-$(CONFIG_RUST) += exports_bindings_generated.h exports_kernel_generated.h
 
 always-$(CONFIG_RUST) += uapi/uapi_generated.rs
 obj-$(CONFIG_RUST) += uapi.o
@@ -60,11 +59,6 @@ endif
 core-cfgs = \
     --cfg no_fp_fmt_parse
 
-alloc-cfgs = \
-    --cfg no_global_oom_handling \
-    --cfg no_rc \
-    --cfg no_sync
-
 quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
       cmd_rustdoc = \
 	OBJTREE=$(abspath $(objtree)) \
@@ -87,7 +81,7 @@ quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
 # command-like flags to solve the issue. Meanwhile, we use the non-custom case
 # and then retouch the generated files.
 rustdoc: rustdoc-core rustdoc-macros rustdoc-compiler_builtins \
-    rustdoc-alloc rustdoc-kernel
+    rustdoc-kernel
 	$(Q)cp $(srctree)/Documentation/images/logo.svg $(rustdoc_output)/static.files/
 	$(Q)cp $(srctree)/Documentation/images/COPYING-logo $(rustdoc_output)/static.files/
 	$(Q)find $(rustdoc_output) -name '*.html' -type f -print0 | xargs -0 sed -Ei \
@@ -111,20 +105,11 @@ rustdoc-core: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
 rustdoc-compiler_builtins: $(src)/compiler_builtins.rs rustdoc-core FORCE
 	+$(call if_changed,rustdoc)
 
-# We need to allow `rustdoc::broken_intra_doc_links` because some
-# `no_global_oom_handling` functions refer to non-`no_global_oom_handling`
-# functions. Ideally `rustdoc` would have a way to distinguish broken links
-# due to things that are "configured out" vs. entirely non-existing ones.
-rustdoc-alloc: private rustc_target_flags = $(alloc-cfgs) \
-    -Arustdoc::broken_intra_doc_links
-rustdoc-alloc: $(RUST_LIB_SRC)/alloc/src/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE
-	+$(call if_changed,rustdoc)
-
-rustdoc-kernel: private rustc_target_flags = --extern alloc \
+rustdoc-kernel: private rustc_target_flags = \
     --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
     --extern bindings --extern uapi
 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
-    rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
+    rustdoc-compiler_builtins $(obj)/libmacros.so \
     $(obj)/bindings.o FORCE
 	+$(call if_changed,rustdoc)
 
@@ -169,7 +154,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 	mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 	OBJTREE=$(abspath $(objtree)) \
 	$(RUSTDOC) --test $(rust_flags) \
-		-L$(objtree)/$(obj) --extern alloc --extern kernel \
+		-L$(objtree)/$(obj) --extern kernel \
 		--extern build_error --extern macros \
 		--extern bindings --extern uapi \
 		--no-run --crate-name kernel -Zunstable-options \
@@ -251,7 +236,7 @@ rusttest-macros: $(src)/macros/lib.rs rusttest-prepare FORCE
 	+$(call if_changed,rustc_test)
 	+$(call if_changed,rustdoc_test)
 
-rusttest-kernel: private rustc_target_flags = --extern alloc \
+rusttest-kernel: private rustc_target_flags = \
     --extern build_error --extern macros --extern bindings --extern uapi
 rusttest-kernel: $(src)/kernel/lib.rs rusttest-prepare \
     rusttestlib-build_error rusttestlib-macros rusttestlib-bindings \
@@ -364,9 +349,6 @@ quiet_cmd_exports = EXPORTS $@
 $(obj)/exports_core_generated.h: $(obj)/core.o FORCE
 	$(call if_changed,exports)
 
-$(obj)/exports_alloc_generated.h: $(obj)/alloc.o FORCE
-	$(call if_changed,exports)
-
 $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
 	$(call if_changed,exports)
 
@@ -402,7 +384,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
 
 rust-analyzer:
 	$(Q)$(srctree)/scripts/generate_rust_analyzer.py \
-		--cfgs='core=$(core-cfgs)' --cfgs='alloc=$(alloc-cfgs)' \
+		--cfgs='core=$(core-cfgs)' \
 		$(realpath $(srctree)) $(realpath $(objtree)) \
 		$(RUST_LIB_SRC) $(KBUILD_EXTMOD) > \
 		$(if $(KBUILD_EXTMOD),$(extmod_prefix),$(objtree))/rust-project.json
@@ -434,12 +416,6 @@ $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
 $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_dep,rustc_library)
 
-$(obj)/alloc.o: private skip_clippy = 1
-$(obj)/alloc.o: private skip_flags = -Dunreachable_pub
-$(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
-$(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
-	+$(call if_changed_dep,rustc_library)
-
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_dep,rustc_library)
 
@@ -454,9 +430,9 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
     $(obj)/uapi/uapi_generated.rs FORCE
 	+$(call if_changed_dep,rustc_library)
 
-$(obj)/kernel.o: private rustc_target_flags = --extern alloc \
+$(obj)/kernel.o: private rustc_target_flags = \
     --extern build_error --extern macros --extern bindings --extern uapi
-$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
+$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o \
     $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
 	+$(call if_changed_dep,rustc_library)
 
diff --git a/rust/exports.c b/rust/exports.c
index 3803c21d1403..1b870e8e83ea 100644
--- a/rust/exports.c
+++ b/rust/exports.c
@@ -16,7 +16,6 @@
 #define EXPORT_SYMBOL_RUST_GPL(sym) extern int sym; EXPORT_SYMBOL_GPL(sym)
 
 #include "exports_core_generated.h"
-#include "exports_alloc_generated.h"
 #include "exports_bindings_generated.h"
 #include "exports_kernel_generated.h"
 
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index efacca63c897..7e7b6b3d5bb9 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -262,18 +262,13 @@ $(obj)/%.lst: $(obj)/%.c FORCE
 
 # Compile Rust sources (.rs)
 # ---------------------------------------------------------------------------
-
-rust_allowed_features := new_uninit
-
 # `--out-dir` is required to avoid temporaries being created by `rustc` in the
 # current working directory, which may be not accessible in the out-of-tree
 # modules case.
 rust_common_cmd = \
 	RUST_MODFILE=$(modfile) $(RUSTC_OR_CLIPPY) $(rust_flags) \
-	-Zallow-features=$(rust_allowed_features) \
 	-Zcrate-attr=no_std \
-	-Zcrate-attr='feature($(rust_allowed_features))' \
-	-Zunstable-options --extern force:alloc --extern kernel \
+	-Zunstable-options --extern kernel \
 	--crate-type rlib -L $(objtree)/rust/ \
 	--crate-name $(basename $(notdir $@)) \
 	--sysroot=/dev/null \
-- 
2.45.2

Re: [PATCH v2 16/23] rust: alloc: implement `collect` for `IntoIter`

[Heghedus Razvan]

On Tue Jul 23, 2024 at 9:10 PM EEST, Danilo Krummrich wrote:
> Currently, we can't implement `FromIterator`. There are a couple of
> issues with this trait in the kernel, namely:
>
>   - Rust's specialization feature is unstable. This prevents us to
>     optimze for the special case where `I::IntoIter` equals `Vec`'s
>     `IntoIter` type.
>   - We also can't use `I::IntoIter`'s type ID either to work around this,
>     since `FromIterator` doesn't require this type to be `'static`.
>   - `FromIterator::from_iter` does return `Self` instead of
>     `Result<Self, AllocError>`, hence we can't properly handle allocation
>     failures.
>   - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle
>     additional allocation flags.
Well that's a shame, so I guess collecting a Filter or Map is not possible.

>
> Instead, provide `IntoIter::collect`, such that we can at least convert
> `IntoIter` into a `Vec` again.
>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 79 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index fbfb755b252d..5c317931e14c 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -2,7 +2,7 @@
>
>  //! Implementation of [`Vec`].
>
> -use super::{AllocError, Allocator, Flags};
> +use super::{flags::*, AllocError, Allocator, Flags};
>  use crate::types::Unique;
>  use core::{
>      fmt,
> @@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A>
>      fn as_raw_mut_slice(&mut self) -> *mut [T] {
>          ptr::slice_from_raw_parts_mut(self.ptr, self.len)
>      }
> +
> +    fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) {
> +        let me = ManuallyDrop::new(self);
> +        let ptr = me.ptr;
> +        let buf = me.buf;
> +        let len = me.len;
> +        let cap = me.cap;
> +        (ptr, buf, len, cap)
> +    }
> +
> +    /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`.
> +    ///
> +    /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait
> +    /// in the kernel, namely:
> +    ///
> +    /// - Rust's specialization feature is unstable. This prevents us to optimze for the special
> +    ///   case where `I::IntoIter` equals `Vec`'s `IntoIter` type.
> +    /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator`
> +    ///   doesn't require this type to be `'static`.
> +    /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence
> +    ///   we can't properly handle allocation failures.
> +    /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation
> +    ///   flags.
> +    ///
> +    /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a
> +    /// `Vec` again.
> +    ///
> +    /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing
> +    /// buffer. However, this backing buffer may be shrunk to the actual count of elements.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// let v = kernel::kvec![1, 2, 3]?;
> +    /// let mut it = v.into_iter();
> +    ///
> +    /// assert_eq!(it.next(), Some(1));
> +    ///
> +    /// let v = it.collect();
> +    /// assert_eq!(v, [2, 3]);
> +    ///
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn collect(self) -> Vec<T, A> {
> +        let (mut ptr, buf, len, mut cap) = self.into_raw_parts();
> +        let has_advanced = ptr != buf.as_ptr();
> +
> +        if has_advanced {
> +            // SAFETY: Copy the contents we have advanced to at the beginning of the buffer.
> +            // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is
> +            // guaranteed to be smaller than `buf.add(cap)`.
> +            unsafe { ptr::copy(ptr, buf.as_ptr(), len) };
> +            ptr = buf.as_ptr();
> +        }
> +
> +        // This can never fail, `len` is guaranteed to be smaller than `cap`.
> +        let layout = core::alloc::Layout::array::<T>(len).unwrap();
> +
> +        // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be
> +        // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves
> +        // it as it is.
> +        ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } {
Here you use `GFP_KERNEL` flag directly. Shouldn't this be an argument of `collect` function? 

> +            // If we fail to shrink, which likely can't even happen, continue with the existing
> +            // buffer.
> +            Err(_) => ptr,
> +            Ok(ptr) => {
> +                cap = len;
> +                ptr.as_ptr().cast()
> +            }
> +        };
> +
> +        // SAFETY: If the iterator has been advanced, the advanced elements have been copied to
> +        // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed
> +        // to point to the start of the backing buffer. `cap` is either the original capacity or,
> +        // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since
> +        // `into_iter` has been called on the original `Vec`.
> +        unsafe { Vec::from_raw_parts(ptr, len, cap) }
> +    }
>  }
>
>  impl<T, A> Iterator for IntoIter<T, A>
> --
> 2.45.2

Re: [PATCH v2 16/23] rust: alloc: implement `collect` for `IntoIter`

[Danilo Krummrich]

On Wed, Jul 24, 2024 at 02:35:46PM +0000, Heghedus Razvan wrote:
> On Tue Jul 23, 2024 at 9:10 PM EEST, Danilo Krummrich wrote:
> > Currently, we can't implement `FromIterator`. There are a couple of
> > issues with this trait in the kernel, namely:
> >
> >   - Rust's specialization feature is unstable. This prevents us to
> >     optimze for the special case where `I::IntoIter` equals `Vec`'s
> >     `IntoIter` type.
> >   - We also can't use `I::IntoIter`'s type ID either to work around this,
> >     since `FromIterator` doesn't require this type to be `'static`.
> >   - `FromIterator::from_iter` does return `Self` instead of
> >     `Result<Self, AllocError>`, hence we can't properly handle allocation
> >     failures.
> >   - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle
> >     additional allocation flags.
> Well that's a shame, so I guess collecting a Filter or Map is not possible.

Not with the Rust's `FromIterator` trait, unfortunately. However, once we have
other collectable data structures in place, we can come up with a kernel
compatible version of the `FromIterator` trait and implement against it.

> 
> >
> > Instead, provide `IntoIter::collect`, such that we can at least convert
> > `IntoIter` into a `Vec` again.
> >
> > Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> > ---
> >  rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 79 insertions(+), 1 deletion(-)
> >
> > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> > index fbfb755b252d..5c317931e14c 100644
> > --- a/rust/kernel/alloc/kvec.rs
> > +++ b/rust/kernel/alloc/kvec.rs
> > @@ -2,7 +2,7 @@
> >
> >  //! Implementation of [`Vec`].
> >
> > -use super::{AllocError, Allocator, Flags};
> > +use super::{flags::*, AllocError, Allocator, Flags};
> >  use crate::types::Unique;
> >  use core::{
> >      fmt,
> > @@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A>
> >      fn as_raw_mut_slice(&mut self) -> *mut [T] {
> >          ptr::slice_from_raw_parts_mut(self.ptr, self.len)
> >      }
> > +
> > +    fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) {
> > +        let me = ManuallyDrop::new(self);
> > +        let ptr = me.ptr;
> > +        let buf = me.buf;
> > +        let len = me.len;
> > +        let cap = me.cap;
> > +        (ptr, buf, len, cap)
> > +    }
> > +
> > +    /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`.
> > +    ///
> > +    /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait
> > +    /// in the kernel, namely:
> > +    ///
> > +    /// - Rust's specialization feature is unstable. This prevents us to optimze for the special
> > +    ///   case where `I::IntoIter` equals `Vec`'s `IntoIter` type.
> > +    /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator`
> > +    ///   doesn't require this type to be `'static`.
> > +    /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence
> > +    ///   we can't properly handle allocation failures.
> > +    /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation
> > +    ///   flags.
> > +    ///
> > +    /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a
> > +    /// `Vec` again.
> > +    ///
> > +    /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing
> > +    /// buffer. However, this backing buffer may be shrunk to the actual count of elements.
> > +    ///
> > +    /// # Examples
> > +    ///
> > +    /// ```
> > +    /// let v = kernel::kvec![1, 2, 3]?;
> > +    /// let mut it = v.into_iter();
> > +    ///
> > +    /// assert_eq!(it.next(), Some(1));
> > +    ///
> > +    /// let v = it.collect();
> > +    /// assert_eq!(v, [2, 3]);
> > +    ///
> > +    /// # Ok::<(), Error>(())
> > +    /// ```
> > +    pub fn collect(self) -> Vec<T, A> {
> > +        let (mut ptr, buf, len, mut cap) = self.into_raw_parts();
> > +        let has_advanced = ptr != buf.as_ptr();
> > +
> > +        if has_advanced {
> > +            // SAFETY: Copy the contents we have advanced to at the beginning of the buffer.
> > +            // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is
> > +            // guaranteed to be smaller than `buf.add(cap)`.
> > +            unsafe { ptr::copy(ptr, buf.as_ptr(), len) };
> > +            ptr = buf.as_ptr();
> > +        }
> > +
> > +        // This can never fail, `len` is guaranteed to be smaller than `cap`.
> > +        let layout = core::alloc::Layout::array::<T>(len).unwrap();
> > +
> > +        // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be
> > +        // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves
> > +        // it as it is.
> > +        ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } {
> Here you use `GFP_KERNEL` flag directly. Shouldn't this be an argument of `collect` function? 

Even though we only ever ask the allocator to shrink the buffer (or keep it as
it is), it should be, good catch!

> 
> > +            // If we fail to shrink, which likely can't even happen, continue with the existing
> > +            // buffer.
> > +            Err(_) => ptr,
> > +            Ok(ptr) => {
> > +                cap = len;
> > +                ptr.as_ptr().cast()
> > +            }
> > +        };
> > +
> > +        // SAFETY: If the iterator has been advanced, the advanced elements have been copied to
> > +        // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed
> > +        // to point to the start of the backing buffer. `cap` is either the original capacity or,
> > +        // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since
> > +        // `into_iter` has been called on the original `Vec`.
> > +        unsafe { Vec::from_raw_parts(ptr, len, cap) }
> > +    }
> >  }
> >
> >  impl<T, A> Iterator for IntoIter<T, A>
> > --
> > 2.45.2
> 
>