rbtree v4 #1081
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rbtree v4 #1081
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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/[email protected]/ [1]
To: Miguel Ojeda <[email protected]>
To: Alex Gaynor <[email protected]>
To: Wedson Almeida Filho <[email protected]>
To: Boqun Feng <[email protected]>
To: Gary Guo <[email protected]>
To: Björn Roy Baron <[email protected]>
To: Benno Lossin <[email protected]>
To: Andreas Hindborg <[email protected]>
To: Alice Ryhl <[email protected]>
To: Greg Kroah-Hartman <[email protected]>
To: Arve Hjønnevåg <[email protected]>
To: Todd Kjos <[email protected]>
To: Martijn Coenen <[email protected]>
To: Joel Fernandes <[email protected]>
To: Christian Brauner <[email protected]>
To: Carlos Llamas <[email protected]>
To: Suren Baghdasaryan <[email protected]>
Cc: Rob Landley <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Matt Gilbride <[email protected]>
---
Changes in v5:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v4: https://lore.kernel.org/r/[email protected]
Changes in v4:
- rebased onto the tip of rust-for-linux/rust-next (97ab3e8)
- addressed comments from draft PR on GitHub: Rust-for-Linux#1081
- Link to v3: https://lore.kernel.org/r/[email protected]
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/[email protected]
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/[email protected]
--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
"series": {
"revision": 5,
"change-id": "20231205-b4-rbtree-abb1a016f0a0",
"prefixes": [],
"history": {
"v1": [
"[email protected]"
],
"v2": [
"[email protected]"
],
"v3": [
"[email protected]"
],
"v4": [
"[email protected]"
]
}
}
}
y86-dev
reviewed
May 28, 2024
rust/kernel/rbtree.rs
Outdated
| @@ -436,21 +455,76 @@ unsafe impl<'a, K: Sync, V: Sync> Sync for Iter<'a, K, V> {} | |||
| impl<'a, K, V> Iterator for Iter<'a, K, V> { | |||
| type Item = (&'a K, &'a V); | |||
|
|
|||
| fn next(&mut self) -> Option<Self::Item> { | |||
| self.iter_raw.next().map(|(k, v)| | |||
| // SAFETY: Due to `&mut self`, we have exclusive access to `k` and `v`, for the lifetime of `'a`. | |||
There was a problem hiding this comment.
This seems wrong, since the Iter only borrows the tree immutably.
Sometimes (see [1]) it is necessary to drop the value inside of a `Box<T>`, but retain the allocation. For example to reuse the allocation in the future. Introduce a new function `drop_contents` that turns a `Box<T>` into `Box<MaybeUninit<T>>` by dropping the value. Signed-off-by: Benno Lossin <[email protected]> Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1]
The rust rbtree exposes a map-like interface over keys and values, backed by the kernel red-black tree implementation. Values can be inserted, deleted, and retrieved from a `RBTree` by key. This base abstraction is used by binder to store key/value pairs and perform lookups, for example the patch "[PATCH RFC 03/20] rust_binder: add threading support" in the binder RFC [1]. Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1] Signed-off-by: Wedson Almeida Filho <[email protected]> Reviewed-by: Alice Ryhl <[email protected]> Tested-by: Alice Ryhl <[email protected]> Signed-off-by: Matt Gilbride <[email protected]>
- Add Iterator implementation for `RBTree`, allowing iteration over (key, value) pairs in key order. - Add individual `keys()` and `values()` functions to iterate over keys or values alone. - Update doctests to use iteration instead of explicitly getting items. Iteration is needed by the binder driver to enumerate all values in a tree for oneway spam detection [1]. Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1] Signed-off-by: Wedson Almeida Filho <[email protected]> Reviewed-by: Alice Ryhl <[email protected]> Tested-by: Alice Ryhl <[email protected]> Signed-off-by: Matt Gilbride <[email protected]>
Add mutable Iterator implementation for `RBTree`, allowing iteration over (key, value) pairs in key order. Only values are mutable, as mutating keys implies modifying a node's position in the tree. Mutable iteration is used by the binder driver during shutdown to clean up the tree maintained by the "range allocator" [1]. Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1] Signed-off-by: Wedson Almeida Filho <[email protected]> Signed-off-by: Matt Gilbride <[email protected]> Reviewed-by: Alice Ryhl <[email protected]> Tested-by: Alice Ryhl <[email protected]>
Add a cursor interface to `RBTree`, supporting the following use cases: - Inspect the current node pointed to by the cursor, inspect/move to it's neighbors in sort order (bidirectionally). - Mutate the tree itself by removing the current node pointed to by the cursor, or one of its neighbors. Add functions to obtain a cursor to the tree by key: - The node with the smallest key - The node with the largest key - The node matching the given key, or the one with the next larger key The cursor abstraction is needed by the binder driver to efficiently search for nodes and (conditionally) modify them, as well as their neighbors [1]. Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1] Co-developed-by: Alice Ryhl <[email protected]> Signed-off-by: Alice Ryhl <[email protected]> Reviewed-by: Alice Ryhl <[email protected]> Tested-by: Alice Ryhl <[email protected]> Signed-off-by: Matt Gilbride <[email protected]>
This mirrors the entry API [1] from the Rust standard library on `RBTree`. This API can be used to access the entry at a specific key and make modifications depending on whether the key is vacant or occupied. This API is useful because it can often be used to avoid traversing the tree multiple times. This is used by binder to look up and conditionally access or insert a value, depending on whether it is there or not [2]. Link: https://doc.rust-lang.org/stable/std/collections/btree_map/enum.Entry.html [1] Link: https://android-review.googlesource.com/c/kernel/common/+/2849906 [2] Signed-off-by: Alice Ryhl <[email protected]> Tested-by: Alice Ryhl <[email protected]> Signed-off-by: Matt Gilbride <[email protected]>
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Responding to Benno's comments here: https://lore.kernel.org/all/[email protected]/