Re: [PATCH v7 0/6] Red-black tree abstraction needed by Rust Binder

[Boqun Feng]

On Fri, Jul 26, 2024 at 07:57:39PM +0000, Matt Gilbride wrote:
> This patchset contains the red-black tree abstractions needed by the Rust
> implementation of the Binder driver.
> 
> Binder driver benefits from O(log n) search/insertion/deletion of
> key/value mappings in various places, including `process.rs` and
> `range_alloc.rs`.  In `range_alloc.rs`, the ability to store and
> search by a generic key type is also useful.
> 
> Please see the Rust Binder RFC for usage examples [1]. Note that
> the `container_of` macro is currently used only by `rbtree` itself.
> 
> Users of "rust: rbtree: add red-black tree implementation backed by the C version"
>     [PATCH RFC 03/20] rust_binder: add threading support
>     [PATCH RFC 05/20] rust_binder: add nodes and context managers
>     [PATCH RFC 06/20] rust_binder: add oneway transactions
> 
> Users of "rust: rbtree: add iterator"
>     [PATCH RFC 17/20] rust_binder: add oneway spam detection
> 
> Users of "rust: rbtree: add mutable iterator"
>     [PATCH RFC 06/20] rust_binder: add oneway transactions
> 
> Users of "rust: rbtree: add `RBTreeCursor`"
>     [PATCH RFC 06/20] rust_binder: add oneway transactions
> 
> Users of "rust: rbtree: add RBTree::entry"
>     Not used in the original RFC, but introduced after further
>     code review.  See: https://r.android.com/2849906
> 
> The Rust Binder RFC addresses the upstream deprecation of red-black
> tree. Quoted here for convenience:
> 
> "This RFC uses the kernel's red-black tree for key/value mappings, but we
> are aware that the red-black tree is deprecated. We did this to make the
> performance comparison more fair, since C binder also uses rbtree for
> this. We intend to replace these with XArrays instead. That said, we
> don't think that XArray is a good fit for the range allocator, and we
> propose to continue using the red-black tree for the range allocator."
> 
> Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-0-08ba9197f637@xxxxxxxxxx/ [1]
> Signed-off-by: Matt Gilbride <mattgilbride@xxxxxxxxxx>

Thanks! For patch #5, there is a small style issue, which can be fixed
by:

diff --git a/rust/kernel/rbtree.rs b/rust/kernel/rbtree.rs
index f6d5162e46f5..96fd45f9dc52 100644
--- a/rust/kernel/rbtree.rs
+++ b/rust/kernel/rbtree.rs
@@ -465,9 +465,7 @@ pub fn cursor_lower_bound(&mut self, key: &K) -> Option<RBTreeCursor<'_, K, V>>
             }
         }
 
-        let Some(best) = best_match else {
-            return None;
-        };
+        let best = best_match?;
 
         // SAFETY: `best` is a non-null node so it is valid by the type invariants.
         let links = unsafe { addr_of_mut!((*best.as_ptr()).links) };

with that, for the whole series:

Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>

I also put this on rust-dev branch for my own testing purpose (with the
above fix applied, and using Benno's version of patch #1 since it's
already in rust-dev).

Regards,
Boqun

> ---
> Changes in v7:
> - make `RawVacantEntry.rbtree` a raw pointer like
>   `RawVacantEntry.child_field_of_parent`, since the latter can
>   technically point at a field of the former. We prefer that the
>   implementation be explicit about the safety guarantees of both because
>   of the relationship between them.
> - Link to v6: https://lore.kernel.org/r/20240711-b4-rbtree-v6-0-14bef1a8cdba@xxxxxxxxxx
> 
> Changes in v6:
> - Minimize usage of `*mut bindings::rb_node`, replacing with
>   `NonNull<bindings::rb_node>`. Specifically, changing
>   `RBTreeCursor.current` to be `NonNull<bindings::rb_node>` and updating
>   the corresponding functions.
> - Update `RBTreeCursor:to_key_value` helpers to have their own lifetime
>   (they are not instance methods, using a different lifetime than that
>   of the `impl` block they are in makes things more clear.
> - Fix misplaced semicolon in `cursor_lower_bound`.
> - Link to v5: https://lore.kernel.org/r/20240606-b4-rbtree-v5-0-96fe1a0e97c0@xxxxxxxxxx
> 
> Changes in v5:
> - Used `Box::write` in `RBTreeNodeReservation::into_node`, removing
>   unnecessary `unsafe` blocks.
> - Updated `RBTreeCursor::remove_current` to return the removed node.
> - Link to v4: https://lore.kernel.org/r/20240603-b4-rbtree-v4-0-308e43d6abfc@xxxxxxxxxx
> 
> Changes in v4:
> - rebased onto the tip of rust-for-linux/rust-next (97ab3e8eec0ce79d9e265e6c9e4c480492180409)
> - addressed comments from draft PR on GitHub: https://github.com/Rust-for-Linux/linux/pull/1081
> - Link to v3: https://lore.kernel.org/r/20240418-b4-rbtree-v3-0-323e134390ce@xxxxxxxxxx
> 
> Changes in v3:
> - Address various feedback re: SAFETY and INVARIANT comments from v2.
> - Update variable naming and add detailed comments for the `RBTree::insert` (later moved to
>   `RBTree::raw_entry`) implementation.
> - Link to v2: https://lore.kernel.org/r/20240219-b4-rbtree-v2-0-0b113aab330d@xxxxxxxxxx
> 
> Changes in v2:
> - Update documentation link to the C header file
> - Use `core::convert::Infallible` in try_reserve_node
> - Link to v1: https://lore.kernel.org/r/20240205-b4-rbtree-v1-0-995e3eee38c0@xxxxxxxxxx
> 
> ---
> Alice Ryhl (1):
>       rust: rbtree: add `RBTree::entry`
> 
> Benno Lossin (1):
>       rust: kernel: add `drop_contents` to `BoxExt`
> 
> Matt Gilbride (1):
>       rust: rbtree: add `RBTreeCursor`
> 
> Wedson Almeida Filho (3):
>       rust: rbtree: add red-black tree implementation backed by the C version
>       rust: rbtree: add iterator
>       rust: rbtree: add mutable iterator
> 
>  rust/helpers.c               |    7 +
>  rust/kernel/alloc/box_ext.rs |   24 +-
>  rust/kernel/lib.rs           |    1 +
>  rust/kernel/rbtree.rs        | 1290 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 1321 insertions(+), 1 deletion(-)
> ---
> base-commit: 97ab3e8eec0ce79d9e265e6c9e4c480492180409
> change-id: 20231205-b4-rbtree-abb1a016f0a0
> 
> Best regards,
> -- 
> Matt Gilbride <mattgilbride@xxxxxxxxxx>
>