linux-kernel - [PATCH v5 4/5] rust: miscdevice: Provide additional abstractions for iov

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Message-ID: <20250822-iov-iter-v5-4-6ce4819c2977@google.com>
Date: Fri, 22 Aug 2025 08:42:35 +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, linux-fsdevel@...r.kernel.org, 
	Alice Ryhl <aliceryhl@...gle.com>, Benno Lossin <lossin@...nel.org>
Subject: [PATCH v5 4/5] 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.

Co-developed-by: Lee Jones <lee@...nel.org>
Signed-off-by: Lee Jones <lee@...nel.org>
Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/miscdevice.rs | 63 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 62 insertions(+), 1 deletion(-)

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.rc2.233.g662b1ed5c5-goog