Merge tag 'alloc-next-v6.16-2025-05-13' of https://github.com/Rust-for-Linux/linux into rust-next

Pull alloc updates from Danilo Krummrich:
 "Box:

   - Support for type coercion, e.g. 'Box<T>' to 'Box<dyn U>' if T
     implements U

  Vec:

   - Implement new methods (prerequisites for nova-core and binder)
      - Vec::truncate()
      - Vec::resize()
      - Vec::clear()
      - Vec::pop()
      - Vec::push_within_capacity()
         - New error type: PushError
      - Vec::drain_all()
      - Vec::retain()
      - Vec::remove()
         - New error type: RemoveError
      - Vec::insert_within_capacity
         - New error type: InsertError

   - Simplify Vec::push() using Vec::spare_capacity_mut()

   - Split Vec::set_len() into Vec::inc_len() and Vec::dec_len()
      - Add type invariant Vec::len() <= Vec::capacity
      - Simplify Vec::truncate() using Vec::dec_len()"

* tag 'alloc-next-v6.16-2025-05-13' of https://github.com/Rust-for-Linux/linux:
  rust: alloc: add Vec::insert_within_capacity
  rust: alloc: add Vec::remove
  rust: alloc: add Vec::retain
  rust: alloc: add Vec::drain_all
  rust: alloc: add Vec::push_within_capacity
  rust: alloc: add Vec::pop
  rust: alloc: add Vec::clear
  rust: alloc: replace `Vec::set_len` with `inc_len`
  rust: alloc: refactor `Vec::truncate` using `dec_len`
  rust: alloc: add `Vec::dec_len`
  rust: alloc: add Vec::len() <= Vec::capacity invariant
  rust: alloc: allow coercion from `Box<T>` to `Box<dyn U>` if T implements U
  rust: alloc: use `spare_capacity_mut` to reduce unsafe
  rust: alloc: add Vec::resize method
  rust: alloc: add Vec::truncate method
  rust: alloc: add missing invariant in Vec::set_len()

1 files changed, 61 insertions, 0 deletions

diff --git a/rust/kernel/alloc/kvec/errors.rs b/rust/kernel/alloc/kvec/errors.rs
new file mode 100644
index 000000000000..348b8d27e102
--- /dev/null
+++ b/rust/kernel/alloc/kvec/errors.rs
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Errors for the [`Vec`] type.
+
+use core::fmt::{self, Debug, Formatter};
+use kernel::prelude::*;
+
+/// Error type for [`Vec::push_within_capacity`].
+pub struct PushError<T>(pub T);
+
+impl<T> Debug for PushError<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "Not enough capacity")
+    }
+}
+
+impl<T> From<PushError<T>> for Error {
+    fn from(_: PushError<T>) -> Error {
+        // Returning ENOMEM isn't appropriate because the system is not out of memory. The vector
+        // is just full and we are refusing to resize it.
+        EINVAL
+    }
+}
+
+/// Error type for [`Vec::remove`].
+pub struct RemoveError;
+
+impl Debug for RemoveError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "Index out of bounds")
+    }
+}
+
+impl From<RemoveError> for Error {
+    fn from(_: RemoveError) -> Error {
+        EINVAL
+    }
+}
+
+/// Error type for [`Vec::insert_within_capacity`].
+pub enum InsertError<T> {
+    /// The value could not be inserted because the index is out of bounds.
+    IndexOutOfBounds(T),
+    /// The value could not be inserted because the vector is out of capacity.
+    OutOfCapacity(T),
+}
+
+impl<T> Debug for InsertError<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            InsertError::IndexOutOfBounds(_) => write!(f, "Index out of bounds"),
+            InsertError::OutOfCapacity(_) => write!(f, "Not enough capacity"),
+        }
+    }
+}
+
+impl<T> From<InsertError<T>> for Error {
+    fn from(_: InsertError<T>) -> Error {
+        EINVAL
+    }
+}