[PATCH 0/9] Add Rust linked list for reference counted values

[Alice Ryhl]

This patchset contains a Rust implementation of a doubly-linked list for
use with reference counted values. Linked lists are famously hard to
implement in Rust [1] given the cyclic nature of the pointers, and
indeed, this implementation uses unsafe to get around that.

Linked lists aren't great for cache locality reasons, but it can be hard
to avoid them for cases where you need data structures that don't
allocate. Most linked lists in Binder are for collections where order
matters (usually stacks or queues). There are also a few lists that are
just collections, but linked lists are only used for this purpose in
cases where the linked list is cold and performance isn't that
important. The linked list is chosen over Vec in this case so that I
don't have to worry about reducing the capacity of the vector. (Our
red/black trees are a much better place to look for improving cache
locality of collections in Rust Binder, and the upcoming xarray bindings
would help with that.)

Please see the Rust Binder RFC [2] for usage examples.

The linked lists are used all over Rust Binder, but some pointers for
where to look for examples:

[PATCH RFC 04/20] rust_binder: add work lists
Implements the work lists that store heterogeneous items. Uses the
various macros a bunch.

[PATCH RFC 10/20] rust_binder: add death notifications
Uses the cursor. Also has objects with multiple prev/next pointer pairs.

[PATCH RFC 15/20] rust_binder: add process freezing
Uses the iterator with for loops.

This patchset depends on [3].

Link: https://rust-unofficial.github.io/too-many-lists/ [1]
Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-0-08ba9197f637@xxxxxxxxxx/ [2]
Link: https://lore.kernel.org/rust-for-linux/20240311-arc-for-list-v3-0-cba1883c62eb@xxxxxxxxxx/ [3]
Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
---
Alice Ryhl (9):
      rust: list: add ListArc
      rust: list: add tracking for ListArc
      rust: list: add struct with prev/next pointers
      rust: list: add macro for implementing ListItem
      rust: list: add List
      rust: list: add iterators
      rust: list: add cursor
      rust: list: support heterogeneous lists
      rust: list: add ListArcField

 rust/kernel/lib.rs                     |   1 +
 rust/kernel/list.rs                    | 637 +++++++++++++++++++++++++++++++++
 rust/kernel/list/arc.rs                | 431 ++++++++++++++++++++++
 rust/kernel/list/arc_field.rs          |  94 +++++
 rust/kernel/list/impl_list_item_mod.rs | 181 ++++++++++
 5 files changed, 1344 insertions(+)
---
base-commit: 98ebc2e1c5bd188fd3140a0f812b302bb9c3ad26
change-id: 20240221-linked-list-25169a90a4de

Best regards,
-- 
Alice Ryhl <aliceryhl@xxxxxxxxxx>