linux-kernel - [PATCH v4 4/6] rust: id_pool: do not supply starting capacity

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Message-ID: <20251110-binder-bitmap-v4-4-5ed8a7fab1b9@google.com>
Date: Mon, 10 Nov 2025 13:05:57 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Yury Norov <yury.norov@...il.com>
Cc: "Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, 
	Martijn Coenen <maco@...roid.com>, Joel Fernandes <joelagnelf@...dia.com>, 
	Christian Brauner <brauner@...nel.org>, Carlos Llamas <cmllamas@...gle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>, Burak Emir <bqe@...gle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v4 4/6] rust: id_pool: do not supply starting capacity

Rust Binder wants to use inline bitmaps whenever possible to avoid
allocations, so introduce a constructor for an IdPool with arbitrary
capacity that stores the bitmap inline.

The existing constructor could be renamed to with_capacity() to match
constructors for other similar types, but it is removed as there is
currently no user for it.

Acked-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
Reviewed-by: Burak Emir <bqe@...gle.com>
Reviewed-by: Danilo Krummrich <dakr@...nel.org>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/id_pool.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/rust/kernel/id_pool.rs b/rust/kernel/id_pool.rs
index 5942f678db015e902fa482eb64c38512a468e449..6f607f04331c9bd3fc79c6d91d04005bd0685839 100644
--- a/rust/kernel/id_pool.rs
+++ b/rust/kernel/id_pool.rs
@@ -95,6 +95,18 @@ pub fn realloc(&self, flags: Flags) -> Result<PoolResizer, AllocError> {
 }
 
 impl IdPool {
+    /// Constructs a new [`IdPool`].
+    ///
+    /// The pool will have a capacity of [`NO_ALLOC_MAX_LEN`].
+    ///
+    /// [`NO_ALLOC_MAX_LEN`]: BitmapVec::NO_ALLOC_MAX_LEN
+    #[inline]
+    pub fn new() -> Self {
+        Self {
+            map: BitmapVec::new_inline(),
+        }
+    }
+
     /// Constructs a new [`IdPool`] with space for a specific number of bits.
     ///
     /// A capacity below [`NO_ALLOC_MAX_LEN`] is adjusted to
@@ -224,3 +236,10 @@ pub fn release_id(&mut self, id: usize) {
         self.map.clear_bit(id);
     }
 }
+
+impl Default for IdPool {
+    #[inline]
+    fn default() -> Self {
+        Self::new()
+    }
+}

-- 
2.51.2.1041.gc1ab5b90ca-goog