From 06cb58b310ea38a8135827f726157df59a95376e Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Fri, 22 Aug 2025 08:42:32 +0000 Subject: [PATCH 1/5] rust: iov: add iov_iter abstractions for ITER_SOURCE This adds abstractions for the iov_iter type in the case where data_source is ITER_SOURCE. This will make Rust implementations of fops->write_iter possible. This series only has support for using existing IO vectors created by C code. Additional abstractions will be needed to support the creation of IO vectors in Rust code. These abstractions make the assumption that `struct iov_iter` does not have internal self-references, which implies that it is valid to move it between different local variables. Reviewed-by: Andreas Hindborg Reviewed-by: Danilo Krummrich Signed-off-by: Alice Ryhl Signed-off-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20250822-iov-iter-v5-1-6ce4819c2977@google.com --- rust/kernel/iov.rs | 171 +++++++++++++++++++++++++++++++++++++++++++++ rust/kernel/lib.rs | 1 + 2 files changed, 172 insertions(+) create mode 100644 rust/kernel/iov.rs diff --git a/rust/kernel/iov.rs b/rust/kernel/iov.rs new file mode 100644 index 000000000000..01f4b90ff8b4 --- /dev/null +++ b/rust/kernel/iov.rs @@ -0,0 +1,171 @@ +// SPDX-License-Identifier: GPL-2.0 + +// Copyright (C) 2025 Google LLC. + +//! IO vectors. +//! +//! C headers: [`include/linux/iov_iter.h`](srctree/include/linux/iov_iter.h), +//! [`include/linux/uio.h`](srctree/include/linux/uio.h) + +use crate::{ + alloc::{Allocator, Flags}, + bindings, + prelude::*, + types::Opaque, +}; +use core::{marker::PhantomData, mem::MaybeUninit, ptr, slice}; + +const ITER_SOURCE: bool = bindings::ITER_SOURCE != 0; + +/// An IO vector that acts as a source of data. +/// +/// The data may come from many different sources. This includes both things in kernel-space and +/// reading from userspace. It's not necessarily the case that the data source is immutable, so +/// rewinding the IO vector to read the same data twice is not guaranteed to result in the same +/// bytes. It's also possible that the data source is mapped in a thread-local manner using e.g. +/// `kmap_local_page()`, so this type is not `Send` to ensure that the mapping is read from the +/// right context in that scenario. +/// +/// # Invariants +/// +/// Must hold a valid `struct iov_iter` with `data_source` set to `ITER_SOURCE`. For the duration +/// of `'data`, it must be safe to read from this IO vector using the standard C methods for this +/// purpose. +#[repr(transparent)] +pub struct IovIterSource<'data> { + iov: Opaque, + /// Represent to the type system that this value contains a pointer to readable data it does + /// not own. + _source: PhantomData<&'data [u8]>, +} + +impl<'data> IovIterSource<'data> { + /// Obtain an `IovIterSource` from a raw pointer. + /// + /// # Safety + /// + /// * The referenced `struct iov_iter` must be valid and must only be accessed through the + /// returned reference for the duration of `'iov`. + /// * The referenced `struct iov_iter` must have `data_source` set to `ITER_SOURCE`. + /// * For the duration of `'data`, it must be safe to read from this IO vector using the + /// standard C methods for this purpose. + #[track_caller] + #[inline] + pub unsafe fn from_raw<'iov>(ptr: *mut bindings::iov_iter) -> &'iov mut IovIterSource<'data> { + // SAFETY: The caller ensures that `ptr` is valid. + let data_source = unsafe { (*ptr).data_source }; + assert_eq!(data_source, ITER_SOURCE); + + // SAFETY: The caller ensures the type invariants for the right durations, and + // `IovIterSource` is layout compatible with `struct iov_iter`. + unsafe { &mut *ptr.cast::>() } + } + + /// Access this as a raw `struct iov_iter`. + #[inline] + pub fn as_raw(&mut self) -> *mut bindings::iov_iter { + self.iov.get() + } + + /// Returns the number of bytes available in this IO vector. + /// + /// Note that this may overestimate the number of bytes. For example, reading from userspace + /// memory could fail with `EFAULT`, which will be treated as the end of the IO vector. + #[inline] + pub fn len(&self) -> usize { + // SAFETY: We have shared access to this IO vector, so we can read its `count` field. + unsafe { + (*self.iov.get()) + .__bindgen_anon_1 + .__bindgen_anon_1 + .as_ref() + .count + } + } + + /// Returns whether there are any bytes left in this IO vector. + /// + /// This may return `true` even if there are no more bytes available. For example, reading from + /// userspace memory could fail with `EFAULT`, which will be treated as the end of the IO vector. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// Advance this IO vector by `bytes` bytes. + /// + /// If `bytes` is larger than the size of this IO vector, it is advanced to the end. + #[inline] + pub fn advance(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector. + unsafe { bindings::iov_iter_advance(self.as_raw(), bytes) }; + } + + /// Advance this IO vector backwards by `bytes` bytes. + /// + /// # Safety + /// + /// The IO vector must not be reverted to before its beginning. + #[inline] + pub unsafe fn revert(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector, and the caller + // ensures that `bytes` is in bounds. + unsafe { bindings::iov_iter_revert(self.as_raw(), bytes) }; + } + + /// Read data from this IO vector. + /// + /// Returns the number of bytes that have been copied. + #[inline] + pub fn copy_from_iter(&mut self, out: &mut [u8]) -> usize { + // SAFETY: `Self::copy_from_iter_raw` guarantees that it will not write any uninitialized + // bytes in the provided buffer, so `out` is still a valid `u8` slice after this call. + let out = unsafe { &mut *(ptr::from_mut(out) as *mut [MaybeUninit]) }; + + self.copy_from_iter_raw(out).len() + } + + /// Read data from this IO vector and append it to a vector. + /// + /// Returns the number of bytes that have been copied. + #[inline] + pub fn copy_from_iter_vec( + &mut self, + out: &mut Vec, + flags: Flags, + ) -> Result { + out.reserve(self.len(), flags)?; + let len = self.copy_from_iter_raw(out.spare_capacity_mut()).len(); + // SAFETY: + // - `len` is the length of a subslice of the spare capacity, so `len` is at most the + // length of the spare capacity. + // - `Self::copy_from_iter_raw` guarantees that the first `len` bytes of the spare capacity + // have been initialized. + unsafe { out.inc_len(len) }; + Ok(len) + } + + /// Read data from this IO vector into potentially uninitialized memory. + /// + /// Returns the sub-slice of the output that has been initialized. If the returned slice is + /// shorter than the input buffer, then the entire IO vector has been read. + /// + /// This will never write uninitialized bytes to the provided buffer. + #[inline] + pub fn copy_from_iter_raw(&mut self, out: &mut [MaybeUninit]) -> &mut [u8] { + let capacity = out.len(); + let out = out.as_mut_ptr().cast::(); + + // GUARANTEES: The C API guarantees that it does not write uninitialized bytes to the + // provided buffer. + // SAFETY: + // * By the type invariants, it is still valid to read from this IO vector. + // * `out` is valid for writing for `capacity` bytes because it comes from a slice of + // that length. + let len = unsafe { bindings::_copy_from_iter(out.cast(), capacity, self.as_raw()) }; + + // SAFETY: The underlying C api guarantees that initialized bytes have been written to the + // first `len` bytes of the spare capacity. + unsafe { slice::from_raw_parts_mut(out, len) } + } +} diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index ed53169e795c..99dbb7b2812e 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -92,6 +92,7 @@ pub mod init; pub mod io; pub mod ioctl; +pub mod iov; pub mod jump_label; #[cfg(CONFIG_KUNIT)] pub mod kunit; From ce2e0829241ab96af9c8a12b511debc5e3188934 Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Fri, 22 Aug 2025 08:42:33 +0000 Subject: [PATCH 2/5] rust: iov: add iov_iter abstractions for ITER_DEST This adds abstractions for the iov_iter type in the case where data_source is ITER_DEST. This will make Rust implementations of fops->read_iter possible. This series only has support for using existing IO vectors created by C code. Additional abstractions will be needed to support the creation of IO vectors in Rust code. These abstractions make the assumption that `struct iov_iter` does not have internal self-references, which implies that it is valid to move it between different local variables. This patch adds an IovIterDest struct that is very similar to the IovIterSource from the previous patch. However, as the methods on the two structs have very little overlap (just getting the length and advance/revert), I do not think it is worth it to try and deduplicate this logic. Reviewed-by: Andreas Hindborg Reviewed-by: Danilo Krummrich Signed-off-by: Alice Ryhl Signed-off-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20250822-iov-iter-v5-2-6ce4819c2977@google.com --- rust/kernel/iov.rs | 143 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 143 insertions(+) diff --git a/rust/kernel/iov.rs b/rust/kernel/iov.rs index 01f4b90ff8b4..43bae8923c46 100644 --- a/rust/kernel/iov.rs +++ b/rust/kernel/iov.rs @@ -16,6 +16,15 @@ use core::{marker::PhantomData, mem::MaybeUninit, ptr, slice}; const ITER_SOURCE: bool = bindings::ITER_SOURCE != 0; +const ITER_DEST: bool = bindings::ITER_DEST != 0; + +// Compile-time assertion for the above constants. +const _: () = { + build_assert!( + ITER_SOURCE != ITER_DEST, + "ITER_DEST and ITER_SOURCE should be different." + ); +}; /// An IO vector that acts as a source of data. /// @@ -169,3 +178,137 @@ pub fn copy_from_iter_raw(&mut self, out: &mut [MaybeUninit]) -> &mut [u8] { unsafe { slice::from_raw_parts_mut(out, len) } } } + +/// An IO vector that acts as a destination for data. +/// +/// IO vectors support many different types of destinations. This includes both buffers in +/// kernel-space and writing to userspace. It's possible that the destination buffer is mapped in a +/// thread-local manner using e.g. `kmap_local_page()`, so this type is not `Send` to ensure that +/// the mapping is written to the right context in that scenario. +/// +/// # Invariants +/// +/// Must hold a valid `struct iov_iter` with `data_source` set to `ITER_DEST`. For the duration of +/// `'data`, it must be safe to write to this IO vector using the standard C methods for this +/// purpose. +#[repr(transparent)] +pub struct IovIterDest<'data> { + iov: Opaque, + /// Represent to the type system that this value contains a pointer to writable data it does + /// not own. + _source: PhantomData<&'data mut [u8]>, +} + +impl<'data> IovIterDest<'data> { + /// Obtain an `IovIterDest` from a raw pointer. + /// + /// # Safety + /// + /// * The referenced `struct iov_iter` must be valid and must only be accessed through the + /// returned reference for the duration of `'iov`. + /// * The referenced `struct iov_iter` must have `data_source` set to `ITER_DEST`. + /// * For the duration of `'data`, it must be safe to write to this IO vector using the + /// standard C methods for this purpose. + #[track_caller] + #[inline] + pub unsafe fn from_raw<'iov>(ptr: *mut bindings::iov_iter) -> &'iov mut IovIterDest<'data> { + // SAFETY: The caller ensures that `ptr` is valid. + let data_source = unsafe { (*ptr).data_source }; + assert_eq!(data_source, ITER_DEST); + + // SAFETY: The caller ensures the type invariants for the right durations, and + // `IovIterSource` is layout compatible with `struct iov_iter`. + unsafe { &mut *ptr.cast::>() } + } + + /// Access this as a raw `struct iov_iter`. + #[inline] + pub fn as_raw(&mut self) -> *mut bindings::iov_iter { + self.iov.get() + } + + /// Returns the number of bytes available in this IO vector. + /// + /// Note that this may overestimate the number of bytes. For example, reading from userspace + /// memory could fail with EFAULT, which will be treated as the end of the IO vector. + #[inline] + pub fn len(&self) -> usize { + // SAFETY: We have shared access to this IO vector, so we can read its `count` field. + unsafe { + (*self.iov.get()) + .__bindgen_anon_1 + .__bindgen_anon_1 + .as_ref() + .count + } + } + + /// Returns whether there are any bytes left in this IO vector. + /// + /// This may return `true` even if there are no more bytes available. For example, reading from + /// userspace memory could fail with EFAULT, which will be treated as the end of the IO vector. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// Advance this IO vector by `bytes` bytes. + /// + /// If `bytes` is larger than the size of this IO vector, it is advanced to the end. + #[inline] + pub fn advance(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector. + unsafe { bindings::iov_iter_advance(self.as_raw(), bytes) }; + } + + /// Advance this IO vector backwards by `bytes` bytes. + /// + /// # Safety + /// + /// The IO vector must not be reverted to before its beginning. + #[inline] + pub unsafe fn revert(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector, and the caller + // ensures that `bytes` is in bounds. + unsafe { bindings::iov_iter_revert(self.as_raw(), bytes) }; + } + + /// Write data to this IO vector. + /// + /// Returns the number of bytes that were written. If this is shorter than the provided slice, + /// then no more bytes can be written. + #[inline] + pub fn copy_to_iter(&mut self, input: &[u8]) -> usize { + // SAFETY: + // * By the type invariants, it is still valid to write to this IO vector. + // * `input` is valid for `input.len()` bytes. + unsafe { bindings::_copy_to_iter(input.as_ptr().cast(), input.len(), self.as_raw()) } + } + + /// Utility for implementing `read_iter` given the full contents of the file. + /// + /// The full contents of the file being read from is represented by `contents`. This call will + /// write the appropriate sub-slice of `contents` and update the file position in `ppos` so + /// that the file will appear to contain `contents` even if takes multiple reads to read the + /// entire file. + #[inline] + pub fn simple_read_from_buffer(&mut self, ppos: &mut i64, contents: &[u8]) -> Result { + if *ppos < 0 { + return Err(EINVAL); + } + let Ok(pos) = usize::try_from(*ppos) else { + return Ok(0); + }; + if pos >= contents.len() { + return Ok(0); + } + + // BOUNDS: We just checked that `pos < contents.len()` above. + let num_written = self.copy_to_iter(&contents[pos..]); + + // OVERFLOW: `pos+num_written <= contents.len() <= isize::MAX <= i64::MAX`. + *ppos = (pos + num_written) as i64; + + Ok(num_written) + } +} From 5e15de179a204ce26623d8468283ac04a0dc672f Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Fri, 22 Aug 2025 08:42:34 +0000 Subject: [PATCH 3/5] rust: fs: add Kiocb struct This adds a very simple Kiocb struct that lets you access the inner file's private data and the file position. For now, nothing else is supported. Cc: Christian Brauner Reviewed-by: Andreas Hindborg Signed-off-by: Alice Ryhl Signed-off-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20250822-iov-iter-v5-3-6ce4819c2977@google.com --- rust/kernel/fs.rs | 3 ++ rust/kernel/fs/kiocb.rs | 68 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) create mode 100644 rust/kernel/fs/kiocb.rs diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs index 0121b38c59e6..6ba6bdf143cb 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 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, + _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) -> ::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 { ::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 } + } +} From 39c2745b37dac18c6604083f26caea3fd7e4c50b Mon Sep 17 00:00:00 2001 From: Alice Ryhl Date: Fri, 22 Aug 2025 08:42:35 +0000 Subject: [PATCH 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 Signed-off-by: Lee Jones Reviewed-by: Andreas Hindborg Signed-off-by: Alice Ryhl Signed-off-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20250822-iov-iter-v5-4-6ce4819c2977@google.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 6373fe183b27..35630fc63875 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 { + build_error!(VTABLE_DEFAULT_ERROR) + } + + /// Write to this miscdevice. + fn write_iter(_kiocb: Kiocb<'_, Self::Ptr>, _iov: &mut IovIterSource<'_>) -> Result { + 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 MiscdeviceVTable { 0 } + /// # Safety + /// + /// `kiocb` must be correspond to a valid file that is associated with a + /// `MiscDeviceRegistration`. `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` 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`. `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` 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`. @@ -341,6 +392,16 @@ impl MiscdeviceVTable { 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 { From e5b0d7da941a7dc1ced09d57b967fdc124f510f8 Mon Sep 17 00:00:00 2001 From: Lee Jones Date: Fri, 22 Aug 2025 08:42:36 +0000 Subject: [PATCH 5/5] samples: rust_misc_device: Expand the sample to support read()ing from userspace A userland application can now operate on the char device with read() in order to consume a locally held buffer. Memory for the buffer is to be provisioned and the buffer populated in its subsequently provided write() counterpart. Signed-off-by: Lee Jones Reviewed-by: Andreas Hindborg Co-developed-by: Alice Ryhl Signed-off-by: Alice Ryhl Signed-off-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20250822-iov-iter-v5-5-6ce4819c2977@google.com --- samples/rust/rust_misc_device.rs | 36 ++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs index e7ab77448f75..9e4005e33796 100644 --- a/samples/rust/rust_misc_device.rs +++ b/samples/rust/rust_misc_device.rs @@ -100,8 +100,9 @@ use kernel::{ c_str, device::Device, - fs::File, + fs::{File, Kiocb}, ioctl::{_IO, _IOC_SIZE, _IOR, _IOW}, + iov::{IovIterDest, IovIterSource}, miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration}, new_mutex, prelude::*, @@ -144,6 +145,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit { struct Inner { value: i32, + buffer: KVVec, } #[pin_data(PinnedDrop)] @@ -165,7 +167,10 @@ fn open(_file: &File, misc: &MiscDeviceRegistration) -> Result) -> Result, iov: &mut IovIterDest<'_>) -> Result { + let me = kiocb.file(); + dev_info!(me.dev, "Reading from Rust Misc Device Sample\n"); + + let inner = me.inner.lock(); + // Read the buffer contents, taking the file position into account. + let read = iov.simple_read_from_buffer(kiocb.ki_pos_mut(), &inner.buffer)?; + + Ok(read) + } + + fn write_iter(mut kiocb: Kiocb<'_, Self::Ptr>, iov: &mut IovIterSource<'_>) -> Result { + let me = kiocb.file(); + dev_info!(me.dev, "Writing to Rust Misc Device Sample\n"); + + let mut inner = me.inner.lock(); + + // Replace buffer contents. + inner.buffer.clear(); + let len = iov.copy_from_iter_vec(&mut inner.buffer, GFP_KERNEL)?; + + // Set position to zero so that future `read` calls will see the new contents. + *kiocb.ki_pos_mut() = 0; + + Ok(len) + } + fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result { dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");