samples: rust_misc_device: Demonstrate additional get/set value functionality

Expand the complexity of the sample driver by providing the ability to
get and set an integer.  The value is protected by a mutex.

Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20241213134715.601415-4-lee@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

samples/rust/rust_misc_device.rs

@@ -4,17 +4,24 @@
 
 //! Rust misc device sample.
 
+use core::pin::Pin;
+
 use kernel::{
     c_str,
     device::Device,
     fs::File,
-    ioctl::_IO,
+    ioctl::{_IO, _IOC_SIZE, _IOR, _IOW},
     miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
+    new_mutex,
     prelude::*,
+    sync::Mutex,
     types::ARef,
+    uaccess::{UserSlice, UserSliceReader, UserSliceWriter},
 };
 
 const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 0x80);
+const RUST_MISC_DEV_GET_VALUE: u32 = _IOR::<i32>('|' as u32, 0x81);
+const RUST_MISC_DEV_SET_VALUE: u32 = _IOW::<i32>('|' as u32, 0x82);
 
 module! {
     type: RustMiscDeviceModule,
@@ -44,44 +51,98 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
     }
 }
 
+struct Inner {
+    value: i32,
+}
+
+#[pin_data(PinnedDrop)]
 struct RustMiscDevice {
+    #[pin]
+    inner: Mutex<Inner>,
     dev: ARef<Device>,
 }
 
 #[vtable]
 impl MiscDevice for RustMiscDevice {
-    type Ptr = KBox<Self>;
+    type Ptr = Pin<KBox<Self>>;
 
-    fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<KBox<Self>> {
+    fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Self>>> {
         let dev = ARef::from(misc.device());
 
         dev_info!(dev, "Opening Rust Misc Device Sample\n");
 
-        Ok(KBox::new(RustMiscDevice { dev }, GFP_KERNEL)?)
+        KBox::try_pin_init(
+            try_pin_init! {
+                RustMiscDevice {
+                    inner <- new_mutex!( Inner{ value: 0_i32 } ),
+                    dev: dev,
+                }
+            },
+            GFP_KERNEL,
+        )
     }
 
-    fn ioctl(
-        me: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
-        _file: &File,
-        cmd: u32,
-        _arg: usize,
-    ) -> Result<isize> {
+    fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result<isize> {
         dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
 
+        let size = _IOC_SIZE(cmd);
+
         match cmd {
-            RUST_MISC_DEV_HELLO => dev_info!(me.dev, "Hello from the Rust Misc Device\n"),
+            RUST_MISC_DEV_GET_VALUE => me.get_value(UserSlice::new(arg, size).writer())?,
+            RUST_MISC_DEV_SET_VALUE => me.set_value(UserSlice::new(arg, size).reader())?,
+            RUST_MISC_DEV_HELLO => me.hello()?,
             _ => {
                 dev_err!(me.dev, "-> IOCTL not recognised: {}\n", cmd);
                 return Err(ENOTTY);
             }
-        }
+        };
 
         Ok(0)
     }
 }
 
-impl Drop for RustMiscDevice {
-    fn drop(&mut self) {
+#[pinned_drop]
+impl PinnedDrop for RustMiscDevice {
+    fn drop(self: Pin<&mut Self>) {
         dev_info!(self.dev, "Exiting the Rust Misc Device Sample\n");
     }
 }
+
+impl RustMiscDevice {
+    fn set_value(&self, mut reader: UserSliceReader) -> Result<isize> {
+        let new_value = reader.read::<i32>()?;
+        let mut guard = self.inner.lock();
+
+        dev_info!(
+            self.dev,
+            "-> Copying data from userspace (value: {})\n",
+            new_value
+        );
+
+        guard.value = new_value;
+        Ok(0)
+    }
+
+    fn get_value(&self, mut writer: UserSliceWriter) -> Result<isize> {
+        let guard = self.inner.lock();
+        let value = guard.value;
+
+        // Free-up the lock and use our locally cached instance from here
+        drop(guard);
+
+        dev_info!(
+            self.dev,
+            "-> Copying data to userspace (value: {})\n",
+            &value
+        );
+
+        writer.write::<i32>(&value)?;
+        Ok(0)
+    }
+
+    fn hello(&self) -> Result<isize> {
+        dev_info!(self.dev, "-> Hello from the Rust Misc Device\n");
+
+        Ok(0)
+    }
+}