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Message-ID: <20250813-iov-iter-v4-3-c4f1932b05ef@google.com>
Date: Wed, 13 Aug 2025 08:27:19 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alexander Viro <viro@...iv.linux.org.uk>,
Arnd Bergmann <arnd@...db.de>, Miguel Ojeda <ojeda@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>,
Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Matthew Maurer <mmaurer@...gle.com>,
Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>,
Benno Lossin <lossin@...nel.org>, Christian Brauner <brauner@...nel.org>
Subject: [PATCH v4 3/4] rust: miscdevice: Provide additional abstractions for
iov_iter and kiocb structures
These will be used for the read_iter() and write_iter() callbacks, which
are now the preferred back-ends for when a user operates on a char device
with read() and write() respectively.
Cc: Christian Brauner <brauner@...nel.org>
Co-developed-by: Lee Jones <lee@...nel.org>
Signed-off-by: Lee Jones <lee@...nel.org>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
rust/kernel/fs.rs | 3 +++
rust/kernel/fs/kiocb.rs | 68 +++++++++++++++++++++++++++++++++++++++++++++++
rust/kernel/miscdevice.rs | 63 ++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 133 insertions(+), 1 deletion(-)
diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs
index 0121b38c59e63d01a89f22c8ef6983ef5c3234de..6ba6bdf143cb991c6e78215178eb585260215da0 100644
--- a/rust/kernel/fs.rs
+++ b/rust/kernel/fs.rs
@@ -6,3 +6,6 @@
pub mod file;
pub use self::file::{File, LocalFile};
+
+mod kiocb;
+pub use self::kiocb::Kiocb;
diff --git a/rust/kernel/fs/kiocb.rs b/rust/kernel/fs/kiocb.rs
new file mode 100644
index 0000000000000000000000000000000000000000..84c936cd69b0e9b490d54c87d8c7279b27d4476a
--- /dev/null
+++ b/rust/kernel/fs/kiocb.rs
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Kernel IO callbacks.
+//!
+//! C headers: [`include/linux/fs.h`](srctree/include/linux/fs.h)
+
+use core::marker::PhantomData;
+use core::ptr::NonNull;
+use kernel::types::ForeignOwnable;
+
+/// Wrapper for the kernel's `struct kiocb`.
+///
+/// Currently this abstractions is incomplete and is essentially just a tuple containing a
+/// reference to a file and a file position.
+///
+/// The type `T` represents the filesystem or driver specific data associated with the file.
+///
+/// # Invariants
+///
+/// `inner` points at a valid `struct kiocb` whose file has the type `T` as its private data.
+pub struct Kiocb<'a, T> {
+ inner: NonNull<bindings::kiocb>,
+ _phantom: PhantomData<&'a T>,
+}
+
+impl<'a, T: ForeignOwnable> Kiocb<'a, T> {
+ /// Create a `Kiocb` from a raw pointer.
+ ///
+ /// # Safety
+ ///
+ /// The pointer must reference a valid `struct kiocb` for the duration of `'a`. The private
+ /// data of the file must be `T`.
+ pub unsafe fn from_raw(kiocb: *mut bindings::kiocb) -> Self {
+ Self {
+ // SAFETY: If a pointer is valid it is not null.
+ inner: unsafe { NonNull::new_unchecked(kiocb) },
+ _phantom: PhantomData,
+ }
+ }
+
+ /// Access the underlying `struct kiocb` directly.
+ pub fn as_raw(&self) -> *mut bindings::kiocb {
+ self.inner.as_ptr()
+ }
+
+ /// Get the filesystem or driver specific data associated with the file.
+ pub fn file(&self) -> <T as ForeignOwnable>::Borrowed<'a> {
+ // SAFETY: We have shared access to this kiocb and hence the underlying file, so we can
+ // read the file's private data.
+ let private = unsafe { (*(*self.as_raw()).ki_filp).private_data };
+ // SAFETY: The kiocb has shared access to the private data.
+ unsafe { <T as ForeignOwnable>::borrow(private) }
+ }
+
+ /// Gets the current value of `ki_pos`.
+ pub fn ki_pos(&self) -> i64 {
+ // SAFETY: We have shared access to the kiocb, so we can read its `ki_pos` field.
+ unsafe { (*self.as_raw()).ki_pos }
+ }
+
+ /// Gets a mutable reference to the `ki_pos` field.
+ pub fn ki_pos_mut(&mut self) -> &mut i64 {
+ // SAFETY: We have exclusive access to the kiocb, so we can write to `ki_pos`.
+ unsafe { &mut (*self.as_raw()).ki_pos }
+ }
+}
diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 6373fe183b2748162988b45d7ed8f563045d3b4d..35630fc638751c416d009fcf0c0ffdf0a4da1218 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -13,7 +13,8 @@
device::Device,
error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
ffi::{c_int, c_long, c_uint, c_ulong},
- fs::File,
+ fs::{File, Kiocb},
+ iov::{IovIterDest, IovIterSource},
mm::virt::VmaNew,
prelude::*,
seq_file::SeqFile,
@@ -141,6 +142,16 @@ fn mmap(
build_error!(VTABLE_DEFAULT_ERROR)
}
+ /// Read from this miscdevice.
+ fn read_iter(_kiocb: Kiocb<'_, Self::Ptr>, _iov: &mut IovIterDest<'_>) -> Result<usize> {
+ build_error!(VTABLE_DEFAULT_ERROR)
+ }
+
+ /// Write to this miscdevice.
+ fn write_iter(_kiocb: Kiocb<'_, Self::Ptr>, _iov: &mut IovIterSource<'_>) -> Result<usize> {
+ build_error!(VTABLE_DEFAULT_ERROR)
+ }
+
/// Handler for ioctls.
///
/// The `cmd` argument is usually manipulated using the utilities in [`kernel::ioctl`].
@@ -245,6 +256,46 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
0
}
+ /// # Safety
+ ///
+ /// `kiocb` must be correspond to a valid file that is associated with a
+ /// `MiscDeviceRegistration<T>`. `iter` must be a valid `struct iov_iter` for writing.
+ unsafe extern "C" fn read_iter(
+ kiocb: *mut bindings::kiocb,
+ iter: *mut bindings::iov_iter,
+ ) -> isize {
+ // SAFETY: The caller provides a valid `struct kiocb` associated with a
+ // `MiscDeviceRegistration<T>` file.
+ let kiocb = unsafe { Kiocb::from_raw(kiocb) };
+ // SAFETY: This is a valid `struct iov_iter` for writing.
+ let iov = unsafe { IovIterDest::from_raw(iter) };
+
+ match T::read_iter(kiocb, iov) {
+ Ok(res) => res as isize,
+ Err(err) => err.to_errno() as isize,
+ }
+ }
+
+ /// # Safety
+ ///
+ /// `kiocb` must be correspond to a valid file that is associated with a
+ /// `MiscDeviceRegistration<T>`. `iter` must be a valid `struct iov_iter` for writing.
+ unsafe extern "C" fn write_iter(
+ kiocb: *mut bindings::kiocb,
+ iter: *mut bindings::iov_iter,
+ ) -> isize {
+ // SAFETY: The caller provides a valid `struct kiocb` associated with a
+ // `MiscDeviceRegistration<T>` file.
+ let kiocb = unsafe { Kiocb::from_raw(kiocb) };
+ // SAFETY: This is a valid `struct iov_iter` for reading.
+ let iov = unsafe { IovIterSource::from_raw(iter) };
+
+ match T::write_iter(kiocb, iov) {
+ Ok(res) => res as isize,
+ Err(err) => err.to_errno() as isize,
+ }
+ }
+
/// # Safety
///
/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
@@ -341,6 +392,16 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
open: Some(Self::open),
release: Some(Self::release),
mmap: if T::HAS_MMAP { Some(Self::mmap) } else { None },
+ read_iter: if T::HAS_READ_ITER {
+ Some(Self::read_iter)
+ } else {
+ None
+ },
+ write_iter: if T::HAS_WRITE_ITER {
+ Some(Self::write_iter)
+ } else {
+ None
+ },
unlocked_ioctl: if T::HAS_IOCTL {
Some(Self::ioctl)
} else {
--
2.51.0.rc0.205.g4a044479a3-goog
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