From patchwork Fri Feb 21 20:27:41 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Tamir Duberstein X-Patchwork-Id: 13986258 Received: from mail-qk1-f175.google.com (mail-qk1-f175.google.com [209.85.222.175]) (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 DDF90253F0D; Fri, 21 Feb 2025 20:27:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.222.175 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740169671; cv=none; b=nvkdCkj1PYrLHut0Y/Sbv56zd3tjW/nPe10WfrXQRzLsmZeopbQEgGoISRZ/r3GZrdEQ35wky0T1LaxoxTW8xngsUDHxqUC/GuJs9RjlWlf4UBOvtzRoKyDgblXMZAYRYHb6GTai5627Yj50mTMVbIOZp33YbRVjvmwdmKFPang= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740169671; c=relaxed/simple; bh=79VkQRszeTKai8h1oQJKIFbB9SETkGd3FPdSPispFCs=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=ik+o3ht+4thyAmlk6b13tSiHY+rsSVf/5ZT7YMVcoLqDneeHwXP2b5g8mG+Q2aiYJSHbyTqWazfD5N8PjgKqaZ6+xhXOFwK9HDA/d9Q6LcfrFuGRsQ1WwUb4XM6bPR+wDK5mTNv1Bs9ilnFGzTqBr5xbhZaSpdu5D6qWI0AQ4iI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=R88BDILB; arc=none smtp.client-ip=209.85.222.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="R88BDILB" Received: by mail-qk1-f175.google.com with SMTP id af79cd13be357-7be8f28172dso175168085a.3; Fri, 21 Feb 2025 12:27:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1740169668; x=1740774468; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=XFXvKkJUD37pdr/9jEL9ZkBZwOEHfbsPm8qU02bWGDg=; b=R88BDILBDw+41+FFWY32YP+KsbCgfBcDzkat+ljSpHRQzTdOkV5EOEOA4/FgoV3Yvs 1W/3tMPy3omK4IZkO0flUhjjNuaduZ2Os9M3wCwJbQY4mfk/JTypiKLJGmWpispoQfQm nzyqZ4Dmhowvfy8HlZy70oPcdUKkqimAsV49YSM3FalUysNXFPY06Xcd/G/3Z4x0dWK6 2K3EBC7IvbcNdqTmv1satDALr4zOLYKRB3OH5T5ecKxb+gnqek/mQucXw/bmtkXXA8l7 D4UvQgUhVwcSHTHAbMBqwgw4alt5EEdqrmlSZOfgiBwl1OpCg4bbwKJHh+84oogWxf+W eoiw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740169668; x=1740774468; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=XFXvKkJUD37pdr/9jEL9ZkBZwOEHfbsPm8qU02bWGDg=; b=fqS/x4NFenYUUUdUXTzzXdvhL25sdrEsrCLRko5FOO35Ia4uBPgrNzuUNFx2hTqd6T tMu3Jo0VXeK+En5x7K1fz6zVzQm24sL0mkK9TxoA2cAXmj93gb6UfRk8luMd02xZi8tX /q1n9nDv58EwvSwi76URRsy/MivTxjhg0PMvMvpkv3UKc5kmBhm4fNtHggccHJ10n6Is +XXwbO4wcs+hfC5XcTJa6xddaR4oFh7C8vJTyIdNSp+3hFGCvD/2EtPYeJF/fVZ7Eer8 v1cAyWZMBEwAYfORMpz+yqW5Pee8Tzq2nCmaLbcLqaK7Npq508ImDAMjOoHlEkuRey33 A0uQ== X-Forwarded-Encrypted: i=1; AJvYcCUBkTlzEsTN4AgRf1fXcNKU6SLe2Zhjt/r/qNajY2G0Tdr7rR13Le6sFjLVfRjR5ptWtLXkj9UKtKlY/PCGcyc=@vger.kernel.org, AJvYcCWi6FNGfVcRYrgxCs/S/53tR3nDzgZK8astfu0e6rdVCAMGfp5luycDxJ5lmbFBYsH1IH5cYLJKxw9lrP3E@vger.kernel.org, AJvYcCXSWMw3OurbwPAhLTYmCVqo/O4p5Gp9diqF/fvR9Z7d7D9F3Yb0cj0/crg6PiQDpVuZMdK17XwOFFVN@vger.kernel.org, AJvYcCXeKTXw5Zg1tW4AtvpuTKUG/0csWvsHf3HIBx9gFEtuXY5KH3RwMzKuBGzb+eA3Jit24cjV6yqCU9ObDqXQ@vger.kernel.org X-Gm-Message-State: AOJu0Yx2kZbx43IR7cp7/AlqYGrMM+/SLz0Bs1vUL5rb7ISWhgJ4FnAW Xb0O8S9JrGK5VzrjryVatDTyQrVvet3P/TiguPUuUlnJvnkIIaft X-Gm-Gg: ASbGncsQe0Ek7JRt77NJu7CfvSvhiEe5AIPHrbzyf5ERgzgyM+apqfVdDhBuiNv+8py QQXwHS37BDqrxgVlTcLwtIHB6TUevVyUFanlIipKmahZesgWa0Xb+Za/E5pSIH3ffBOzxNE6pfp 7lfE1qCh4lOJu+V2/4Y/0kgGxed3KnzIigo3bSzq8SUer1a2TPcPciRBINbxAIILINd0ImDU0I+ djbzaXhQG29VlEhIv90DNmo3NLoaIrsYoMn4uIbKhimz1KOkFg+5V64hn+bDG+HiNfsW0vCn/uO 2RiwYZPELGsgVdMSGdzIdqFvLOj8/N3dHYxnu7QPD+ZUtQwWWA== X-Google-Smtp-Source: AGHT+IGG40wmJBIe3UfeV3nvKhEypy7SjBjMM7cZnhd8thtWl2fJLRx4zMaodX5KMlEP/uRKGtAM3Q== X-Received: by 2002:a05:620a:2801:b0:7c0:b3cd:9bc7 with SMTP id af79cd13be357-7c0ceeeae37mr692165785a.3.1740169667560; Fri, 21 Feb 2025 12:27:47 -0800 (PST) Received: from tamird-mac.local ([2600:4041:5be7:7c00:880f:47d4:56c6:b852]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c0a99d363csm539224985a.70.2025.02.21.12.27.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Feb 2025 12:27:47 -0800 (PST) From: Tamir Duberstein Date: Fri, 21 Feb 2025 15:27:41 -0500 Subject: [PATCH v18 2/3] rust: xarray: Add an abstraction for XArray Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250221-rust-xarray-bindings-v18-2-cbabe5ddfc32@gmail.com> References: <20250221-rust-xarray-bindings-v18-0-cbabe5ddfc32@gmail.com> In-Reply-To: <20250221-rust-xarray-bindings-v18-0-cbabe5ddfc32@gmail.com> To: Danilo Krummrich , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Matthew Wilcox , Bjorn Helgaas , Greg Kroah-Hartman , "Rafael J. Wysocki" , Tamir Duberstein , FUJITA Tomonori , "Rob Herring (Arm)" Cc: =?utf-8?q?Ma=C3=ADra_Canal?= , Asahi Lina , rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org X-Mailer: b4 0.15-dev `XArray` is an efficient sparse array of pointers. Add a Rust abstraction for this type. This implementation bounds the element type on `ForeignOwnable` and requires explicit locking for all operations. Future work may leverage RCU to enable lockless operation. Inspired-by: Maíra Canal Inspired-by: Asahi Lina Reviewed-by: Andreas Hindborg Reviewed-by: Alice Ryhl Signed-off-by: Tamir Duberstein --- rust/bindings/bindings_helper.h | 6 + rust/helpers/helpers.c | 1 + rust/helpers/xarray.c | 28 ++++ rust/kernel/lib.rs | 1 + rust/kernel/xarray.rs | 277 ++++++++++++++++++++++++++++++++++++++++ 5 files changed, 313 insertions(+) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index f46cf3bb7069..18a40a83453d 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -35,6 +35,7 @@ #include #include #include +#include #include /* `bindgen` gets confused at certain things. */ @@ -48,3 +49,8 @@ const gfp_t RUST_CONST_HELPER___GFP_ZERO = __GFP_ZERO; const gfp_t RUST_CONST_HELPER___GFP_HIGHMEM = ___GFP_HIGHMEM; const gfp_t RUST_CONST_HELPER___GFP_NOWARN = ___GFP_NOWARN; const blk_features_t RUST_CONST_HELPER_BLK_FEAT_ROTATIONAL = BLK_FEAT_ROTATIONAL; + +const xa_mark_t RUST_CONST_HELPER_XA_PRESENT = XA_PRESENT; + +const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC = XA_FLAGS_ALLOC; +const gfp_t RUST_CONST_HELPER_XA_FLAGS_ALLOC1 = XA_FLAGS_ALLOC1; diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c index 0640b7e115be..6811f71f2cbb 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -35,3 +35,4 @@ #include "vmalloc.c" #include "wait.c" #include "workqueue.c" +#include "xarray.c" diff --git a/rust/helpers/xarray.c b/rust/helpers/xarray.c new file mode 100644 index 000000000000..60b299f11451 --- /dev/null +++ b/rust/helpers/xarray.c @@ -0,0 +1,28 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include + +int rust_helper_xa_err(void *entry) +{ + return xa_err(entry); +} + +void rust_helper_xa_init_flags(struct xarray *xa, gfp_t flags) +{ + return xa_init_flags(xa, flags); +} + +int rust_helper_xa_trylock(struct xarray *xa) +{ + return xa_trylock(xa); +} + +void rust_helper_xa_lock(struct xarray *xa) +{ + return xa_lock(xa); +} + +void rust_helper_xa_unlock(struct xarray *xa) +{ + return xa_unlock(xa); +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 398242f92a96..e6e49dcdcb4c 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -85,6 +85,7 @@ pub mod types; pub mod uaccess; pub mod workqueue; +pub mod xarray; #[doc(hidden)] pub use bindings; diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs new file mode 100644 index 000000000000..58ea5cf8c314 --- /dev/null +++ b/rust/kernel/xarray.rs @@ -0,0 +1,277 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! XArray abstraction. +//! +//! C header: [`include/linux/xarray.h`](srctree/include/linux/xarray.h) + +use crate::{ + alloc, bindings, build_assert, + error::{Error, Result}, + init::PinInit, + pin_init, + types::{ForeignOwnable, NotThreadSafe, Opaque}, +}; +use core::{iter, marker::PhantomData, mem, pin::Pin, ptr::NonNull}; +use macros::{pin_data, pinned_drop}; + +/// An array which efficiently maps sparse integer indices to owned objects. +/// +/// This is similar to a [`crate::alloc::kvec::Vec>`], but more efficient when there are +/// holes in the index space, and can be efficiently grown. +/// +/// # Invariants +/// +/// `self.xa` is always an initialized and valid [`bindings::xarray`] whose entries are either +/// `XA_ZERO_ENTRY` or came from `T::into_foreign`. +/// +/// # Examples +/// +/// ```rust +/// use kernel::alloc::KBox; +/// use kernel::xarray::{AllocKind, XArray}; +/// +/// let xa = KBox::pin_init(XArray::new(AllocKind::Alloc1), GFP_KERNEL)?; +/// +/// let dead = KBox::new(0xdead, GFP_KERNEL)?; +/// let beef = KBox::new(0xbeef, GFP_KERNEL)?; +/// +/// let mut guard = xa.lock(); +/// +/// assert_eq!(guard.get(0), None); +/// +/// assert_eq!(guard.store(0, dead, GFP_KERNEL)?.as_deref(), None); +/// assert_eq!(guard.get(0).copied(), Some(0xdead)); +/// +/// *guard.get_mut(0).unwrap() = 0xffff; +/// assert_eq!(guard.get(0).copied(), Some(0xffff)); +/// +/// assert_eq!(guard.store(0, beef, GFP_KERNEL)?.as_deref().copied(), Some(0xffff)); +/// assert_eq!(guard.get(0).copied(), Some(0xbeef)); +/// +/// guard.remove(0); +/// assert_eq!(guard.get(0), None); +/// +/// # Ok::<(), Error>(()) +/// ``` +#[pin_data(PinnedDrop)] +pub struct XArray { + #[pin] + xa: Opaque, + _p: PhantomData, +} + +#[pinned_drop] +impl PinnedDrop for XArray { + fn drop(self: Pin<&mut Self>) { + self.iter().for_each(|ptr| { + let ptr = ptr.as_ptr(); + // SAFETY: `ptr` came from `T::into_foreign`. + // + // INVARIANT: we own the only reference to the array which is being dropped so the + // broken invariant is not observable on function exit. + drop(unsafe { T::from_foreign(ptr) }) + }); + + // SAFETY: `self.xa` is always valid by the type invariant. + unsafe { bindings::xa_destroy(self.xa.get()) }; + } +} + +/// Flags passed to [`XArray::new`] to configure the array's allocation tracking behavior. +pub enum AllocKind { + /// Consider the first element to be at index 0. + Alloc, + /// Consider the first element to be at index 1. + Alloc1, +} + +impl XArray { + /// Creates a new initializer for this type. + pub fn new(kind: AllocKind) -> impl PinInit { + let flags = match kind { + AllocKind::Alloc => bindings::XA_FLAGS_ALLOC, + AllocKind::Alloc1 => bindings::XA_FLAGS_ALLOC1, + }; + pin_init!(Self { + // SAFETY: `xa` is valid while the closure is called. + // + // INVARIANT: `xa` is initialized here to an empty, valid [`bindings::xarray`]. + xa <- Opaque::ffi_init(|xa| unsafe { + bindings::xa_init_flags(xa, flags) + }), + _p: PhantomData, + }) + } + + fn iter(&self) -> impl Iterator> + '_ { + let mut index = 0; + + // SAFETY: `self.xa` is always valid by the type invariant. + iter::once(unsafe { + bindings::xa_find(self.xa.get(), &mut index, usize::MAX, bindings::XA_PRESENT) + }) + .chain(iter::from_fn(move || { + // SAFETY: `self.xa` is always valid by the type invariant. + Some(unsafe { + bindings::xa_find_after(self.xa.get(), &mut index, usize::MAX, bindings::XA_PRESENT) + }) + })) + .map_while(|ptr| NonNull::new(ptr.cast())) + } + + /// Attempts to lock the [`XArray`] for exclusive access. + pub fn try_lock(&self) -> Option> { + // SAFETY: `self.xa` is always valid by the type invariant. + if (unsafe { bindings::xa_trylock(self.xa.get()) } != 0) { + Some(Guard { + xa: self, + _not_send: NotThreadSafe, + }) + } else { + None + } + } + + /// Locks the [`XArray`] for exclusive access. + pub fn lock(&self) -> Guard<'_, T> { + // SAFETY: `self.xa` is always valid by the type invariant. + unsafe { bindings::xa_lock(self.xa.get()) }; + + Guard { + xa: self, + _not_send: NotThreadSafe, + } + } +} + +/// A lock guard. +/// +/// The lock is unlocked when the guard goes out of scope. +#[must_use = "the lock unlocks immediately when the guard is unused"] +pub struct Guard<'a, T: ForeignOwnable> { + xa: &'a XArray, + _not_send: NotThreadSafe, +} + +impl Drop for Guard<'_, T> { + fn drop(&mut self) { + // SAFETY: + // - `self.xa.xa` is always valid by the type invariant. + // - The caller holds the lock, so it is safe to unlock it. + unsafe { bindings::xa_unlock(self.xa.xa.get()) }; + } +} + +/// The error returned by [`store`](Guard::store). +/// +/// Contains the underlying error and the value that was not stored. +pub struct StoreError { + /// The error that occurred. + pub error: Error, + /// The value that was not stored. + pub value: T, +} + +impl From> for Error { + fn from(value: StoreError) -> Self { + self.error + } +} + +impl<'a, T: ForeignOwnable> Guard<'a, T> { + fn load(&self, index: usize, f: F) -> Option + where + F: FnOnce(NonNull) -> U, + { + // SAFETY: `self.xa.xa` is always valid by the type invariant. + let ptr = unsafe { bindings::xa_load(self.xa.xa.get(), index) }; + let ptr = NonNull::new(ptr.cast())?; + Some(f(ptr)) + } + + /// Provides a reference to the element at the given index. + pub fn get(&self, index: usize) -> Option> { + self.load(index, |ptr| { + // SAFETY: `ptr` came from `T::into_foreign`. + unsafe { T::borrow(ptr.as_ptr()) } + }) + } + + /// Provides a mutable reference to the element at the given index. + pub fn get_mut(&mut self, index: usize) -> Option> { + self.load(index, |ptr| { + // SAFETY: `ptr` came from `T::into_foreign`. + unsafe { T::borrow_mut(ptr.as_ptr()) } + }) + } + + /// Removes and returns the element at the given index. + pub fn remove(&mut self, index: usize) -> Option { + // SAFETY: + // - `self.xa.xa` is always valid by the type invariant. + // - The caller holds the lock. + let ptr = unsafe { bindings::__xa_erase(self.xa.xa.get(), index) }.cast(); + // SAFETY: + // - `ptr` is either NULL or came from `T::into_foreign`. + // - `&mut self` guarantees that the lifetimes of [`T::Borrowed`] and [`T::BorrowedMut`] + // borrowed from `self` have ended. + unsafe { T::try_from_foreign(ptr) } + } + + /// Stores an element at the given index. + /// + /// May drop the lock if needed to allocate memory, and then reacquire it afterwards. + /// + /// On success, returns the element which was previously at the given index. + /// + /// On failure, returns the element which was attempted to be stored. + pub fn store( + &mut self, + index: usize, + value: T, + gfp: alloc::Flags, + ) -> Result, StoreError> { + build_assert!( + mem::align_of::() >= 4, + "pointers stored in XArray must be 4-byte aligned" + ); + let new = value.into_foreign(); + + let old = { + let new = new.cast(); + // SAFETY: + // - `self.xa.xa` is always valid by the type invariant. + // - The caller holds the lock. + // + // INVARIANT: `new` came from `T::into_foreign`. + unsafe { bindings::__xa_store(self.xa.xa.get(), index, new, gfp.as_raw()) } + }; + + // SAFETY: `__xa_store` returns the old entry at this index on success or `xa_err` if an + // error happened. + let errno = unsafe { bindings::xa_err(old) }; + if errno != 0 { + // SAFETY: `new` came from `T::into_foreign` and `__xa_store` does not take + // ownership of the value on error. + let value = unsafe { T::from_foreign(new) }; + Err(StoreError { + value, + error: Error::from_errno(errno), + }) + } else { + let old = old.cast(); + // SAFETY: `ptr` is either NULL or came from `T::into_foreign`. + // + // NB: `XA_ZERO_ENTRY` is never returned by functions belonging to the Normal XArray + // API; such entries present as `NULL`. + Ok(unsafe { T::try_from_foreign(old) }) + } + } +} + +// SAFETY: `XArray` has no shared mutable state so it is `Send` iff `T` is `Send`. +unsafe impl Send for XArray {} + +// SAFETY: `XArray` serialises the interior mutability it provides so it is `Sync` iff `T` is +// `Send`. +unsafe impl Sync for XArray {}