Merge patch series "Rust support for `struct iov_iter`"

Alice Ryhl <aliceryhl@google.com> says:

This series adds support for the `struct iov_iter` type. This type
represents an IO buffer for reading or writing, and can be configured
for either direction of communication.

In Rust, we define separate types for reading and writing. This will
ensure that you cannot mix them up and e.g. call copy_from_iter in a
read_iter syscall.

To use the new abstractions, miscdevices are given new methods read_iter
and write_iter that can be used to implement the read/write syscalls on
a miscdevice. The miscdevice sample is updated to provide read/write
operations.

Intended for Greg's miscdevice tree.

Link: https://lore.kernel.org/r/20250822-iov-iter-v5-0-6ce4819c2977@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 68 insertions, 0 deletions

diff --git a/rust/kernel/fs/kiocb.rs b/rust/kernel/fs/kiocb.rs
new file mode 100644
index 000000000000..84c936cd69b0
--- /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 }
+    }
+}