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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 <lee@kernel.org>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Co-developed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250822-iov-iter-v5-5-6ce4819c2977@google.com
This commit is contained in:
Lee Jones 2025-08-22 08:42:36 +00:00 committed by Greg Kroah-Hartman
parent 39c2745b37
commit e5b0d7da94
1 changed files with 34 additions and 2 deletions
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36
samples/rust/rust_misc_device.rs
View File

@ -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<Self, Error> {
struct Inner {
value: i32,
buffer: KVVec<u8>,
}
#[pin_data(PinnedDrop)]
@ -165,7 +167,10 @@ fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Se
KBox::try_pin_init(
try_pin_init! {
RustMiscDevice {
inner <- new_mutex!( Inner{ value: 0_i32 } ),
inner <- new_mutex!(Inner {
value: 0_i32,
buffer: KVVec::new(),
}),
dev: dev,
}
},
@ -173,6 +178,33 @@ fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Se
)
}
fn read_iter(mut kiocb: Kiocb<'_, Self::Ptr>, iov: &mut IovIterDest<'_>) -> Result<usize> {
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<usize> {
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<isize> {
dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");