From nobody Wed Dec 17 12:25:57 2025 Received: from mail-wr1-f73.google.com (mail-wr1-f73.google.com [209.85.221.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DD96F19E819 for ; Thu, 27 Mar 2025 16:16:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743092203; cv=none; b=ZX5v6LHgac/x5RXgWttUwgjSXDMhgYT/AlfYA5uD1pslKYCw12Z+gDvXKQ0J1v5M1HkBNMIg9Gtx7OTolAzg5aZsELLoeKTJ4Gv3urmdI4vQERN2rd4XEdZegOKWr2RTNg6wSc9L6SuXq6PIw6Tb1AHwS3lbowVi8i0UFSRv1iA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743092203; c=relaxed/simple; bh=F+x+UW53qVwetpZ4xzLhdPdzOKCpWVY/5F+38EvXfyE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=qAr79mfjd13wJ+Re8mqTBJphKZvHhDHuFNCAs0YdqKWsS8ztuS1bVpt2FxPV0YisDUG34TnBVbO6kQiBN6d+st+dYFnPHzajunW2qUC0Fvl+xot+9lS4szMk8+/pP7yMQoCozDC/zwtHR+mehsRX7KYgMNP07BbIDRfEib1z8uQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--bqe.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=wrNtItv6; arc=none smtp.client-ip=209.85.221.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--bqe.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="wrNtItv6" Received: by mail-wr1-f73.google.com with SMTP id ffacd0b85a97d-391492acb59so752635f8f.3 for ; Thu, 27 Mar 2025 09:16:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1743092200; x=1743697000; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=CaI5jeiepnCukVYTE/StOGk7ZSuQkrGrfxX0IW/jO00=; b=wrNtItv6YvDhyUHvL1iRO/l9NhCK4zZmB+V1HpXSvMWjqb65+e9DYWEbWTsfDIAstK dI60ENuK9Cjias/AhF20ByhxHnPZvcp+C+ZfRxnfWfHBWqpzElFhm/pMPoKHER7D1wsR BSx+186h/vaXIoSMOAnSxt5NykiaL/mFMcyxno3rzE0z43/ZEv2YLxl8AmCNj7jrkzGi vsS/6MDif2lVGvZaMtpL1VyAeDGztqSukBL+b02ZqId6LyXpTOp6wGkc27PEsEtpIcH9 PzGef+t/t0SjpemAX9ur6c5sXkbhfD8XcOmSrXzidXSDa/po3WqyIXaR8GxyfOkbeNsk QszQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1743092200; x=1743697000; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=CaI5jeiepnCukVYTE/StOGk7ZSuQkrGrfxX0IW/jO00=; b=wPxHCbbj/ofFbKrQjQbctvqOJYvNk3X/I0Eh/L+7/5DSiS3sL0I+fZmFxgv/egetH9 UqHs1KSkISA/D0Unh2GzwVKWQoyrinnJRjNobsOTMTdTBKCQJIUvlkDZc60FJLD5PrEU GNtvmy2aCeIDWw9hDFFg2d2OpJXZWz/w3uVMTVi8KmCcSYxrC8HpcLrvaBeo8gFAuDIM IKcTtbeVGMEQj9LvcM0O1Iz4h51A4Zvfa4erOF0iYQV0pndxpcvYqf+GumP2bdqk19ib 3vNFByS3srJtRq5zrQukP8hu9fcylJJ7BvKjT9SkgvQdN0UiKQ2DPzNMII0My1zZivjd vkQg== X-Forwarded-Encrypted: i=1; AJvYcCVII16f/CA7IW3VKRTrklMQtdL+TjSD2Xt2YmcZUPS/ezw5vGTTyYBnOFPszM+xyMQWLLFuZyBTiry4Z6M=@vger.kernel.org X-Gm-Message-State: AOJu0YyLBOI2NWSfWd0FPOpfetx6DOKGA2upN8QJw1Wd48XU+yxMFXmr mNxJ9x50SXt9BhQcqGDw3JkQXvKecjV+6hj0jB3O+YV846dS75yZNN/SbeGW3Hfqog== X-Google-Smtp-Source: AGHT+IGMNNLBeGoFDGM/YN3dohqRU/VHAkNClOFV3WlHWzboKThygC1+BFMBGcJLJZuE8N9hNGiNS+c= X-Received: from wmdd9.prod.google.com ([2002:a05:600c:a209:b0:43d:896f:72e5]) (user=bqe job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6000:40e0:b0:399:7f43:b3a4 with SMTP id ffacd0b85a97d-39ad1748dc1mr3646412f8f.24.1743092200090; Thu, 27 Mar 2025 09:16:40 -0700 (PDT) Date: Thu, 27 Mar 2025 16:16:14 +0000 In-Reply-To: <20250327161617.117748-1-bqe@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250327161617.117748-1-bqe@google.com> X-Mailer: git-send-email 2.49.0.395.g12beb8f557-goog Message-ID: <20250327161617.117748-5-bqe@google.com> Subject: [PATCH v6 4/4] rust: add dynamic ID pool abstraction for bitmap From: Burak Emir To: Yury Norov Cc: Burak Emir , Rasmus Villemoes , Viresh Kumar , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This is a port of the Binder data structure introduced in commit 15d9da3f818c ("binder: use bitmap for faster descriptor lookup") to Rust. Like drivers/android/dbitmap.h, the ID pool abstraction lets clients acquire and release IDs. The implementation uses a bitmap to know what IDs are in use, and gives clients fine-grained control over the time of allocation. This fine-grained control is needed in the Android Binder. We provide an example that release a spinlock for allocation and unit tests (rustdoc examples). The implementation is not aware that the underlying Bitmap abstraction handles lengths below BITS_PER_LONG without allocation. Suggested-by: Alice Ryhl Suggested-by: Yury Norov Signed-off-by: Burak Emir --- MAINTAINERS | 1 + rust/kernel/id_pool.rs | 201 +++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 3 files changed, 203 insertions(+) create mode 100644 rust/kernel/id_pool.rs diff --git a/MAINTAINERS b/MAINTAINERS index efb0d367dea2..13bc1c695858 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4040,6 +4040,7 @@ M: Burak Emir R: Yury Norov S: Maintained F: rust/kernel/bitmap.rs +F: rust/kernel/id_pool.rs =20 BITOPS API M: Yury Norov diff --git a/rust/kernel/id_pool.rs b/rust/kernel/id_pool.rs new file mode 100644 index 000000000000..8f07526bb580 --- /dev/null +++ b/rust/kernel/id_pool.rs @@ -0,0 +1,201 @@ +// SPDX-License-Identifier: GPL-2.0 + +// Copyright (C) 2025 Google LLC. + +//! Rust API for an ID pool backed by a `Bitmap`. + +use crate::alloc::{AllocError, Flags}; +use crate::bitmap::Bitmap; + +/// Represents a dynamic ID pool backed by a `Bitmap`. +/// +/// Clients acquire and release IDs from zero bits in a bitmap. +/// +/// The ID pool can grow or shrink as needed. It has been designed +/// to support the scenario where users need to control the time +/// of allocation of a new backing bitmap, which may require release +/// of locks. +/// These operations then, are verified to determine if the grow or +/// shrink is sill valid. +/// +/// # Examples +/// +/// Basic usage +/// +/// ``` +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL}; +/// use kernel::id_pool::IdPool; +/// +/// let mut pool =3D IdPool::new(64, GFP_KERNEL)?; +/// for i in 0..64 { +/// assert_eq!(i, pool.acquire_next_id(i).ok_or(ENOSPC)?); +/// } +/// +/// pool.release_id(23); +/// assert_eq!(23, pool.acquire_next_id(0).ok_or(ENOSPC)?); +/// +/// assert_eq!(None, pool.acquire_next_id(0)); // time to realloc. +/// let resizer =3D pool.grow_alloc().alloc(GFP_KERNEL)?; +/// pool.grow(resizer); +/// +/// assert_eq!(pool.acquire_next_id(0), Some(64)); +/// # Ok::<(), Error>(()) +/// ``` +/// +/// Releasing spinlock to grow the pool +/// +/// ```no_run +/// use kernel::alloc::{AllocError, flags::GFP_KERNEL}; +/// use kernel::sync::{new_spinlock, SpinLock}; +/// use kernel::id_pool::IdPool; +/// +/// fn get_id_maybe_alloc(guarded_pool: &SpinLock) -> Result { +/// let mut pool =3D guarded_pool.lock(); +/// loop { +/// match pool.acquire_next_id(0) { +/// Some(index) =3D> return Ok(index), +/// None =3D> { +/// let alloc_request =3D pool.grow_alloc(); +/// drop(pool); +/// let resizer =3D alloc_request.alloc(GFP_KERNEL)?; +/// pool =3D guarded_pool.lock(); +/// pool.grow(resizer) +/// } +/// } +/// } +/// } +/// ``` +pub struct IdPool { + map: Bitmap, +} + +/// Returned when the `IdPool` should change size. +pub struct AllocRequest { + nbits: usize, +} + +/// Contains an allocated `Bitmap` for resizing `IdPool`. +pub struct PoolResizer { + new: Bitmap, +} + +impl AllocRequest { + /// Allocates a new `Bitmap` for `IdPool`. + pub fn alloc(&self, flags: Flags) -> Result { + let new =3D Bitmap::new(self.nbits, flags)?; + Ok(PoolResizer { new }) + } +} + +impl IdPool { + /// Constructs a new `[IdPool]`. + #[inline] + pub fn new(nbits: usize, flags: Flags) -> Result { + let map =3D Bitmap::new(nbits, flags)?; + Ok(Self { map }) + } + + /// Returns how many IDs this pool can currently have. + #[inline] + pub fn len(&self) -> usize { + self.map.len() + } + + /// Returns an [`AllocRequest`] if the [`IdPool`] can be shrunk, [`Non= e`] otherwise. + /// + /// # Examples + /// + /// ``` + /// use kernel::alloc::{AllocError, flags::GFP_KERNEL}; + /// use kernel::id_pool::{AllocRequest, IdPool}; + /// + /// let mut pool =3D IdPool::new(1024, GFP_KERNEL)?; + /// let alloc_request =3D pool.shrink_alloc().ok_or(AllocError)?; + /// let resizer =3D alloc_request.alloc(GFP_KERNEL)?; + /// pool.shrink(resizer); + /// assert_eq!(pool.len(), kernel::bindings::BITS_PER_LONG as usize); + /// # Ok::<(), AllocError>(()) + /// ``` + #[inline] + pub fn shrink_alloc(&self) -> Option { + let len =3D self.map.len(); + if len <=3D bindings::BITS_PER_LONG as usize { + return None; + } + /* + * Determine if the bitmap can shrink based on the position of + * its last set bit. If the bit is within the first quarter of + * the bitmap then shrinking is possible. In this case, the + * bitmap should shrink to half its current size. + */ + match self.map.last_bit() { + Some(bit) =3D> { + if bit < (len >> 2) { + Some(AllocRequest { nbits: len >> 1 }) + } else { + None + } + } + None =3D> Some(AllocRequest { + nbits: bindings::BITS_PER_LONG as usize, + }), + } + } + + /// Shrinks pool by using a new `Bitmap`, if still possible. + #[inline] + pub fn shrink(&mut self, mut resizer: PoolResizer) { + // Verify that shrinking is still possible. The `resizer` + // bitmap might have been allocated without locks, so this call + // could now be outdated. In this case, drop `resizer` and move on. + if let Some(AllocRequest { nbits }) =3D self.shrink_alloc() { + if nbits <=3D resizer.new.len() { + resizer.new.copy_and_extend(&self.map); + self.map =3D resizer.new; + return; + } + } + } + + /// Returns an `AllocRequest` for growing this `IdPool`. + #[inline] + pub fn grow_alloc(&self) -> AllocRequest { + AllocRequest { + nbits: self.map.len() << 1, + } + } + + /// Grows pool by using a new `Bitmap`, if still necessary. + #[inline] + pub fn grow(&mut self, mut resizer: PoolResizer) { + // `resizer` bitmap might have been allocated without locks, + // so this call could now be outdated. In this case, drop + // `resizer` and move on. + if resizer.new.len() <=3D self.map.len() { + return; + } + + resizer.new.copy_and_extend(&self.map); + self.map =3D resizer.new; + } + + /// Acquires a new ID by finding and setting the next zero bit in the + /// bitmap. Upon success, returns its index. Otherwise, returns `None` + /// to indicate that a `grow_alloc` is needed. + #[inline] + pub fn acquire_next_id(&mut self, offset: usize) -> Option { + match self.map.next_zero_bit(offset) { + res @ Some(nr) =3D> { + self.map.set_bit(nr); + res + } + None =3D> None, + } + } + + /// Releases an ID. + #[inline] + pub fn release_id(&mut self, id: usize) { + self.map.clear_bit(id); + } +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index c82b23236056..fc19d97f7b9b 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -51,6 +51,7 @@ #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)] pub mod firmware; pub mod fs; +pub mod id_pool; pub mod init; pub mod io; pub mod ioctl; --=20 2.49.0.395.g12beb8f557-goog