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Fri, 22 Aug 2025 05:56:45 -0700 (PDT) Received: from sidong.sidong.yang.office.furiosa.vpn ([175.195.128.78]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b4764003537sm7194544a12.25.2025.08.22.05.56.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 Aug 2025 05:56:44 -0700 (PDT) From: Sidong Yang To: Jens Axboe , Daniel Almeida , Caleb Sander Mateos , Benno Lossin Cc: Miguel Ojeda , Arnd Bergmann , Greg Kroah-Hartman , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, io-uring@vger.kernel.org, Sidong Yang Subject: [RFC PATCH v3 3/5] rust: io_uring: introduce rust abstraction for io-uring cmd Date: Fri, 22 Aug 2025 12:55:53 +0000 Message-ID: <20250822125555.8620-4-sidong.yang@furiosa.ai> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250822125555.8620-1-sidong.yang@furiosa.ai> References: <20250822125555.8620-1-sidong.yang@furiosa.ai> Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Implment the io-uring abstractions needed for miscdevicecs and other char devices that have io-uring command interface. * `io_uring::IoUringCmd` : Rust abstraction for `io_uring_cmd` which will be used as arg for `MiscDevice::uring_cmd()`. And driver can get `cmd_op` sent from userspace. Also it has `flags` which includes option that is reissued. * `io_uring::IoUringSqe` : Rust abstraction for `io_uring_sqe` which could be get from `IoUringCmd::sqe()` and driver could get `cmd_data` from userspace. Also `IoUringSqe` has more data like opcode could be used in driver. Signed-off-by: Sidong Yang --- rust/kernel/io_uring.rs | 306 ++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 2 files changed, 307 insertions(+) create mode 100644 rust/kernel/io_uring.rs diff --git a/rust/kernel/io_uring.rs b/rust/kernel/io_uring.rs new file mode 100644 index 000000000000..61e88bdf4e42 --- /dev/null +++ b/rust/kernel/io_uring.rs @@ -0,0 +1,306 @@ +// SPDX-License-Identifier: GPL-2.0 +// SPDX-FileCopyrightText: (C) 2025 Furiosa AI + +//! Abstractions for io-uring. +//! +//! This module provides types for implements io-uring interface for char device. +//! +//! +//! C headers: [`include/linux/io_uring/cmd.h`](srctree/include/linux/io_uring/cmd.h) and +//! [`include/linux/io_uring/io_uring.h`](srctree/include/linux/io_uring/io_uring.h) + +use core::{mem::MaybeUninit, pin::Pin}; + +use crate::error::from_result; +use crate::transmute::{AsBytes, FromBytes}; +use crate::{fs::File, types::Opaque}; + +use crate::prelude::*; + +/// io-uring opcode +pub mod opcode { + /// opcode for uring cmd + pub const URING_CMD: u32 = bindings::io_uring_op_IORING_OP_URING_CMD; +} + +/// A Rust abstraction for the Linux kernel's `io_uring_cmd` structure. +/// +/// This structure is a safe, opaque wrapper around the raw C `io_uring_cmd` +/// binding from the Linux kernel. It represents a command structure used +/// in io_uring operations within the kernel. +/// This type is used internally by the io_uring subsystem to manage +/// asynchronous I/O commands. +/// +/// This type should not be constructed or manipulated directly by +/// kernel module developers. +/// +/// # INVARIANT +/// - `self.inner` always points to a valid, live `bindings::io_uring_cmd`. +#[repr(transparent)] +pub struct IoUringCmd { + /// An opaque wrapper containing the actual `io_uring_cmd` data. + inner: Opaque, +} + +impl IoUringCmd { + /// Returns the cmd_op with associated with the `io_uring_cmd`. + #[inline] + pub fn cmd_op(&self) -> u32 { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + unsafe { (*self.inner.get()).cmd_op } + } + + /// Returns the flags with associated with the `io_uring_cmd`. + #[inline] + pub fn flags(&self) -> u32 { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + unsafe { (*self.inner.get()).flags } + } + + /// Reads protocol data unit as `T` that impl `FromBytes` from uring cmd + /// + /// Fails with [`EFAULT`] if size of `T` is bigger than pdu size. + #[inline] + pub fn read_pdu(&self) -> Result { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + let inner = unsafe { &mut *self.inner.get() }; + + let len = size_of::(); + if len > inner.pdu.len() { + return Err(EFAULT); + } + + let mut out: MaybeUninit = MaybeUninit::uninit(); + let ptr = &raw mut inner.pdu as *const c_void; + + // SAFETY: + // * The `ptr` is valid pointer from `self.inner` that is guaranteed by type invariant. + // * The `out` is valid pointer that points `T` which impls `FromBytes` and checked + // size of `T` is smaller than pdu size. + unsafe { + core::ptr::copy_nonoverlapping(ptr, out.as_mut_ptr().cast::(), len); + } + + // SAFETY: The read above has initialized all bytes in `out`, and since `T` implements + // `FromBytes`, any bit-pattern is a valid value for this type. + Ok(unsafe { out.assume_init() }) + } + + /// Writes the provided `value` to `pdu` in uring_cmd `self` + /// + /// Fails with [`EFAULT`] if size of `T` is bigger than pdu size. + #[inline] + pub fn write_pdu(&mut self, value: &T) -> Result<()> { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + let inner = unsafe { &mut *self.inner.get() }; + + let len = size_of::(); + if len > inner.pdu.len() { + return Err(EFAULT); + } + + let src = (value as *const T).cast::(); + let dst = &raw mut inner.pdu as *mut c_void; + + // SAFETY: + // * The `src` is points valid memory that is guaranteed by `T` impls `AsBytes` + // * The `dst` is valid. It's from `self.inner` that is guaranteed by type invariant. + // * It's safe to copy because size of `T` is no more than len of pdu. + unsafe { + core::ptr::copy_nonoverlapping(src, dst, len); + } + + Ok(()) + } + + /// Constructs a new [`IoUringCmd`] from a raw `io_uring_cmd` + /// + /// # Safety + /// + /// The caller must guarantee that: + /// - `ptr` is non-null, properly aligned, and points to a valid + /// `bindings::io_uring_cmd`. + /// - The pointed-to memory remains initialized and valid for the entire + /// lifetime `'a` of the returned reference. + /// - While the returned `Pin<&'a mut IoUringCmd>` is alive, the underlying + /// object is **not moved** (pinning requirement). + /// - **Aliasing rules:** the returned `&mut` has **exclusive** access to the same + /// object for its entire lifetime: + /// - No other `&mut` **or** `&` references to the same `io_uring_cmd` may be + /// alive at the same time. + /// - There must be no concurrent reads/writes through raw pointers, FFI, or + /// other kernel paths to the same object during this lifetime. + /// - If the object can be touched from other contexts (e.g. IRQ/another CPU), + /// the caller must provide synchronization to uphold this exclusivity. + /// - This function relies on `IoUringCmd` being `repr(transparent)` over + /// `bindings::io_uring_cmd` so the cast preserves layout. + #[inline] + pub unsafe fn from_raw<'a>(ptr: *mut bindings::io_uring_cmd) -> Pin<&'a mut IoUringCmd> { + // SAFETY: + // * The caller guarantees that the pointer is not dangling and stays + // valid for the duration of 'a. + // * The cast is okay because `IoUringCmd` is `repr(transparent)` and + // has the same memory layout as `bindings::io_uring_cmd`. + // * The returned `Pin` ensures that the object cannot be moved, which + // is required because the kernel may hold pointers to this memory + // location and moving it would invalidate those pointers. + unsafe { Pin::new_unchecked(&mut *ptr.cast()) } + } + + /// Returns the file that referenced by uring cmd self. + #[inline] + pub fn file(&self) -> &File { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + let file = unsafe { (*self.inner.get()).file }; + + // SAFETY: + // * The `file` points valid file. + // * refcount is positive after submission queue entry issued. + // * There is no active fdget_pos region on the file on this thread. + unsafe { File::from_raw_file(file) } + } + + /// Returns an reference to the [`IoUringSqe`] associated with this command. + #[inline] + pub fn sqe(&self) -> &IoUringSqe { + // SAFETY: `self.inner` is guaranteed by the type invariant to point + // to a live `io_uring_cmd`, so dereferencing is safe. + let sqe = unsafe { (*self.inner.get()).sqe }; + // SAFETY: The call guarantees that the `sqe` points valid io_uring_sqe. + unsafe { IoUringSqe::from_raw(sqe) } + } + + /// Completes an this [`IoUringCmd`] request that was previously queued. + /// + /// # Safety + /// + /// - This function must be called **only** for a command whose `uring_cmd` + /// handler previously returned **`-EIOCBQUEUED`** to io_uring. + /// + /// # Parameters + /// + /// - `ret`: Result to return to userspace. + /// - `res2`: Extra for big completion queue entry `IORING_SETUP_CQE32`. + /// - `issue_flags`: Flags associated with this request, typically the same + /// as those passed to the `uring_cmd` handler. + #[inline] + pub fn done(self: Pin<&mut IoUringCmd>, ret: Result, res2: u64, issue_flags: u32) { + let ret = from_result(|| ret) as isize; + // SAFETY: The call guarantees that `self.inner` is not dangling and stays valid + unsafe { + bindings::io_uring_cmd_done(self.inner.get(), ret, res2, issue_flags); + } + } +} + +/// A Rust abstraction for the Linux kernel's `io_uring_sqe` structure. +/// +/// This structure is a safe, opaque wrapper around the raw C [`io_uring_sqe`](srctree/include/uapi/linux/io_uring.h) +/// binding from the Linux kernel. It represents a Submission Queue Entry +/// used in io_uring operations within the kernel. +/// +/// # Type Safety +/// +/// The `#[repr(transparent)]` attribute ensures that this wrapper has +/// the same memory layout as the underlying `io_uring_sqe` structure, +/// allowing it to be safely transmuted between the two representations. +/// +/// # Fields +/// +/// * `inner` - An opaque wrapper containing the actual `io_uring_sqe` data. +/// The `Opaque` type prevents direct access to the internal +/// structure fields, ensuring memory safety and encapsulation. +/// +/// # Usage +/// +/// This type represents a submission queue entry that describes an I/O +/// operation to be executed by the io_uring subsystem. It contains +/// information such as the operation type, file descriptor, buffer +/// pointers, and other operation-specific data. +/// +/// Users can obtain this type from [`IoUringCmd::sqe()`] method, which +/// extracts the submission queue entry associated with a command. +/// +/// This type should not be constructed or manipulated directly by +/// kernel module developers. +/// +/// # INVARIANT +/// - `self.inner` always points to a valid, live `bindings::io_uring_sqe`. +#[repr(transparent)] +pub struct IoUringSqe { + inner: Opaque, +} + +impl IoUringSqe { + /// Reads and interprets the `cmd` field of an `bindings::io_uring_sqe` as a value of type `T`. + /// + /// # Safety & Invariants + /// - Construction of `T` is delegated to `FromBytes`, which guarantees that `T` has no + /// invalid bit patterns and can be safely reconstructed from raw bytes. + /// - **Limitation:** This implementation does not support `IORING_SETUP_SQE128` (larger SQE entries). + /// Only the standard `io_uring_sqe` layout is handled here. + /// + /// # Errors + /// * Returns `EINVAL` if the `self` does not hold a `opcode::URING_CMD`. + /// * Returns `EFAULT` if the command buffer is smaller than the requested type `T`. + /// + /// # Returns + /// * On success, returns a `T` deserialized from the `cmd`. + /// * On failure, returns an appropriate error as described above. + pub fn cmd_data(&self) -> Result { + // SAFETY: `self.inner` guaranteed by the type invariant to point + // to a live `io_uring_sqe`, so dereferencing is safe. + let sqe = unsafe { &*self.inner.get() }; + + if u32::from(sqe.opcode) != opcode::URING_CMD { + return Err(EINVAL); + } + + // SAFETY: Accessing the `sqe.cmd` union field is safe because we've + // verified that `sqe.opcode == IORING_OP_URING_CMD`, which guarantees + // that this union variant is initialized and valid. + let cmd = unsafe { sqe.__bindgen_anon_6.cmd.as_ref() }; + let cmd_len = size_of_val(&sqe.__bindgen_anon_6.bindgen_union_field); + + if cmd_len < size_of::() { + return Err(EFAULT); + } + + let cmd_ptr = cmd.as_ptr() as *mut T; + + // SAFETY: `cmd_ptr` is valid from `self.inner` which is guaranteed by + // type variant. And also it points to initialized `T` from userspace. + let ret = unsafe { core::ptr::read_unaligned(cmd_ptr) }; + + Ok(ret) + } + + /// Constructs a new `IoUringSqe` from a raw `io_uring_sqe`. + /// + /// # Safety + /// + /// The caller must guarantee that: + /// - `ptr` is non-null, properly aligned, and points to a valid initialized + /// `bindings::io_uring_sqe`. + /// - The pointed-to memory remains valid (not freed or repurposed) for the + /// entire lifetime `'a` of the returned reference. + /// - **Aliasing rules (for `&T`):** while the returned `&'a IoUringSqe` is + /// alive, there must be **no mutable access** to the same object through any + /// path (no `&mut`, no raw-pointer writes, no FFI/IRQ/other-CPU writers). + /// Multiple `&` is fine **only if all of them are read-only** for the entire + /// overlapping lifetime. + /// - This relies on `IoUringSqe` being `repr(transparent)` over + /// `bindings::io_uring_sqe`, so the cast preserves layout. + #[inline] + pub unsafe fn from_raw<'a>(ptr: *const bindings::io_uring_sqe) -> &'a IoUringSqe { + // SAFETY: The caller guarantees that the pointer is not dangling and stays valid for the + // duration of 'a. The cast is okay because `IoUringSqe` is `repr(transparent)` and has the + // same memory layout as `bindings::io_uring_sqe`. + unsafe { &*ptr.cast() } + } +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index ed53169e795c..d38cf7137401 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -91,6 +91,7 @@ pub mod fs; pub mod init; pub mod io; +pub mod io_uring; pub mod ioctl; pub mod jump_label; #[cfg(CONFIG_KUNIT)] -- 2.43.0