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Fri, 13 Dec 2024 11:55:40 -0800 (PST) Received: from 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa ([2620:10d:c091:600::1:e1cd]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-467b2ca087esm1047261cf.28.2024.12.13.11.55.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Dec 2024 11:55:39 -0800 (PST) From: Tamir Duberstein Date: Fri, 13 Dec 2024 14:55:18 -0500 Subject: [PATCH v13 2/2] 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: <20241213-rust-xarray-bindings-v13-2-8655164e624f@gmail.com> References: <20241213-rust-xarray-bindings-v13-0-8655164e624f@gmail.com> In-Reply-To: <20241213-rust-xarray-bindings-v13-0-8655164e624f@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 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, Tamir Duberstein 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/alloc.rs | 5 + rust/kernel/lib.rs | 1 + rust/kernel/xarray.rs | 289 ++++++++++++++++++++++++++++++++++++++++ 6 files changed, 330 insertions(+) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 5c4dfe22f41a5a106330e8c43ffbd342c69c4e0b..9f39d673b240281aed2759b5bd076aa43fb54951 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -30,6 +30,7 @@ #include #include #include +#include #include /* `bindgen` gets confused at certain things. */ @@ -43,3 +44,8 @@ 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 dcf827a61b52e71e46fd5378878602eef5e538b6..ff28340e78c53c79baf18e2927cc90350d8ab513 100644 --- a/rust/helpers/helpers.c +++ b/rust/helpers/helpers.c @@ -30,3 +30,4 @@ #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 0000000000000000000000000000000000000000..60b299f11451d2c4a75e50e25dec4dac13f143f4 --- /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/alloc.rs b/rust/kernel/alloc.rs index f2f7f3a53d298cf899e062346202ba3285ce3676..be9f164ece2e0fe71143e0201247d2b70c193c51 100644 --- a/rust/kernel/alloc.rs +++ b/rust/kernel/alloc.rs @@ -39,6 +39,11 @@ pub struct Flags(u32); impl Flags { + /// Get a flags value with all bits unset. + pub fn empty() -> Self { + Self(0) + } + /// Get the raw representation of this flag. pub(crate) fn as_raw(self) -> u32 { self.0 diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index e1065a7551a39e68d6379031d80d4be336e652a3..9ca524b15920c525c7db419e60dec4c43522751d 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -68,6 +68,7 @@ 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 0000000000000000000000000000000000000000..e320198301e14413e9d54e8c457e399eeebcb4a4 --- /dev/null +++ b/rust/kernel/xarray.rs @@ -0,0 +1,289 @@ +// 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, build_error, + 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 [`XArray`]. + 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. + xa <- Opaque::ffi_init(|xa| unsafe { + bindings::xa_init_flags(xa, flags) + }), + _p: PhantomData, + }) + } + + fn iter(&self) -> impl Iterator> + '_ { + // TODO: Remove and use usize::MAX when + // https://lore.kernel.org/all/20240913213041.395655-5-gary@garyguo.net/ is applied. + const MAX: crate::ffi::c_ulong = crate::ffi::c_ulong::MAX; + + 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, 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, 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()) }; + } +} + +// TODO: Remove when https://lore.kernel.org/all/20240913213041.395655-5-gary@garyguo.net/ is applied. +fn to_index(i: usize) -> crate::ffi::c_ulong { + i.try_into() + .unwrap_or_else(|_| build_error!("cannot convert usize to c_ulong")) +} + +/// 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 { + let StoreError { error, value: _ } = value; + 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(), to_index(index)) }; + let ptr = NonNull::new(ptr.cast())?; + Some(f(ptr)) + } + + /// Loads an entry from the array. + /// + /// Returns the entry 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()) } + }) + } + + /// Loads an entry from the array. + /// + /// Returns the entry 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()) } + }) + } + + /// Erases an entry from the array. + /// + /// Returns the entry which was previously at the given index. + pub fn remove(&mut self, index: usize) -> Option { + // SAFETY: `self.xa.xa` is always valid by the type invariant. + // + // SAFETY: The caller holds the lock. + let ptr = unsafe { bindings::__xa_erase(self.xa.xa.get(), to_index(index)) }.cast(); + // SAFETY: `ptr` is either NULL or came from `T::into_foreign`. + unsafe { T::try_from_foreign(ptr) } + } + + /// Stores an entry in the array. + /// + /// May drop the lock if needed to allocate memory, and then reacquire it afterwards. + /// + /// On success, returns the entry which was previously at the given index. + /// + /// On failure, returns the entry 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. + // + // SAFETY: The caller holds the lock. + // + // INVARIANT: `new` came from `T::into_foreign`. + unsafe { bindings::__xa_store(self.xa.xa.get(), to_index(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 {}