[PATCH v6 0/5] rust: miscdevice: Provide sample driver using the new MiscDevice bindings

[PATCH v6 0/5] rust: miscdevice: Provide sample driver using the new MiscDevice bindings

[Lee Jones]

This set depends on Alice's most recent MiscDevice changes:

https://lore.kernel.org/all/20241210-miscdevice-file-param-v3-0-b2a79b666dc5@google.com/

Changelog v5 -> v6:
 - pr_info() to dev_info() conversion (based on Alice's new set)
 - Moved the example C program from the commit message to the file comments
 - Changed mutex-drop commentary

Lee Jones (5):
  Documentation: ioctl-number: Carve out some identifiers for use by
    sample drivers
  samples: rust: Provide example using the new Rust MiscDevice
    abstraction
  samples: rust_misc_device: Demonstrate additional get/set value
    functionality
  MAINTAINERS: Add Rust Misc Sample to MISC entry
  samples: rust_misc_device: Provide an example C program to exercise
    functionality

 .../userspace-api/ioctl/ioctl-number.rst      |   1 +
 MAINTAINERS                                   |   1 +
 samples/rust/Kconfig                          |  10 +
 samples/rust/Makefile                         |   1 +
 samples/rust/rust_misc_device.rs              | 238 ++++++++++++++++++
 5 files changed, 251 insertions(+)
 create mode 100644 samples/rust/rust_misc_device.rs

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v6 1/5] Documentation: ioctl-number: Carve out some identifiers for use by sample drivers

[Lee Jones]

32 IDs should be plenty (at yet, not too greedy) since a lot of sample
drivers will use their own subsystem allocations.

Sample drivers predominately reside in <KERNEL_ROOT>/samples, but there
should be no issue with in-place example drivers using them.

Signed-off-by: Lee Jones <lee@kernel.org>
---
 Documentation/userspace-api/ioctl/ioctl-number.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index 243f1f1b554a..dc4bc0cab69f 100644
--- a/Documentation/userspace-api/ioctl/ioctl-number.rst
+++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
@@ -311,6 +311,7 @@ Code  Seq#    Include File                                           Comments
                                                                      <mailto:oe@port.de>
 'z'   10-4F  drivers/s390/crypto/zcrypt_api.h                        conflict!
 '|'   00-7F  linux/media.h
+'|'   80-9F  samples/                                                Any sample and example drivers
 0x80  00-1F  linux/fb.h
 0x81  00-1F  linux/vduse.h
 0x89  00-06  arch/x86/include/asm/sockios.h
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v6 2/5] samples: rust: Provide example using the new Rust MiscDevice abstraction

[Lee Jones]

This sample driver demonstrates the following basic operations:

* Register a Misc Device
* Create /dev/rust-misc-device
* Provide open call-back for the aforementioned character device
* Operate on the character device via a simple ioctl()
* Provide close call-back for the character device

Signed-off-by: Lee Jones <lee@kernel.org>
---
 samples/rust/Kconfig             | 10 ++++
 samples/rust/Makefile            |  1 +
 samples/rust/rust_misc_device.rs | 87 ++++++++++++++++++++++++++++++++
 3 files changed, 98 insertions(+)
 create mode 100644 samples/rust/rust_misc_device.rs

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index b0f74a81c8f9..df384e679901 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -20,6 +20,16 @@ config SAMPLE_RUST_MINIMAL
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_MISC_DEVICE
+	tristate "Misc device"
+	help
+	  This option builds the Rust misc device.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_misc_device.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_PRINT
 	tristate "Printing macros"
 	help
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index c1a5c1655395..ad4b97a98580 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -2,6 +2,7 @@
 ccflags-y += -I$(src)				# needed for trace events
 
 obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
+obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
new file mode 100644
index 000000000000..324c3696ae3f
--- /dev/null
+++ b/samples/rust/rust_misc_device.rs
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Rust misc device sample.
+
+use kernel::{
+    c_str,
+    device::Device,
+    fs::File,
+    ioctl::_IO,
+    miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
+    prelude::*,
+    types::ARef,
+};
+
+const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 0x80);
+
+module! {
+    type: RustMiscDeviceModule,
+    name: "rust_misc_device",
+    author: "Lee Jones",
+    description: "Rust misc device sample",
+    license: "GPL",
+}
+
+#[pin_data]
+struct RustMiscDeviceModule {
+    #[pin]
+    _miscdev: MiscDeviceRegistration<RustMiscDevice>,
+}
+
+impl kernel::InPlaceModule for RustMiscDeviceModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        pr_info!("Initialising Rust Misc Device Sample\n");
+
+        let options = MiscDeviceOptions {
+            name: c_str!("rust-misc-device"),
+        };
+
+        try_pin_init!(Self {
+            _miscdev <- MiscDeviceRegistration::register(options),
+        })
+    }
+}
+
+struct RustMiscDevice {
+    dev: ARef<Device>,
+}
+
+#[vtable]
+impl MiscDevice for RustMiscDevice {
+    type Ptr = KBox<Self>;
+
+    fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<KBox<Self>> {
+        let dev = ARef::from(misc.device());
+
+        dev_info!(dev, "Opening Rust Misc Device Sample\n");
+
+        Ok(KBox::new(RustMiscDevice { dev }, GFP_KERNEL)?)
+    }
+
+    fn ioctl(
+        me: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
+        cmd: u32,
+        _arg: usize,
+    ) -> Result<isize> {
+        dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
+
+        match cmd {
+            RUST_MISC_DEV_HELLO => dev_info!(me.dev, "Hello from the Rust Misc Device\n"),
+            _ => {
+                dev_err!(me.dev, "-> IOCTL not recognised: {}\n", cmd);
+                return Err(ENOTTY);
+            }
+        }
+
+        Ok(0)
+    }
+}
+
+impl Drop for RustMiscDevice {
+    fn drop(&mut self) {
+        dev_info!(self.dev, "Exiting the Rust Misc Device Sample\n");
+    }
+}
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v6 3/5] samples: rust_misc_device: Demonstrate additional get/set value functionality

[Lee Jones]

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>
---
 samples/rust/rust_misc_device.rs | 89 +++++++++++++++++++++++++++-----
 1 file changed, 75 insertions(+), 14 deletions(-)

diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index 324c3696ae3f..ae1474a451f1 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/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)
+    }
+}
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v6 4/5] MAINTAINERS: Add Rust Misc Sample to MISC entry

[Lee Jones]

Signed-off-by: Lee Jones <lee@kernel.org>
---
 MAINTAINERS | 1 +
 1 file changed, 1 insertion(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 81348dbce8ca..d3e3b20e0376 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5346,6 +5346,7 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
 F:	drivers/char/
 F:	drivers/misc/
 F:	include/linux/miscdevice.h
+F:	samples/rust/rust_misc_device.rs
 X:	drivers/char/agp/
 X:	drivers/char/hw_random/
 X:	drivers/char/ipmi/
-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH v6 5/5] samples: rust_misc_device: Provide an example C program to exercise functionality

[Lee Jones]

Here is the expected output (manually spliced together):

USERSPACE: Opening /dev/rust-misc-device for reading and writing
KERNEL: rust_misc_device: Opening Rust Misc Device Sample
USERSPACE: Calling Hello
KERNEL: rust_misc_device: IOCTLing Rust Misc Device Sample
KERNEL: rust_misc_device: -> Hello from the Rust Misc Device
USERSPACE: Fetching initial value
KERNEL: rust_misc_device: IOCTLing Rust Misc Device Sample
KERNEL: rust_misc_device: -> Copying data to userspace (value: 0)
USERSPACE: Submitting new value (1)
KERNEL: rust_misc_device: IOCTLing Rust Misc Device Sample
KERNEL: rust_misc_device: -> Copying data from userspace (value: 1)
USERSPACE: Fetching new value
KERNEL: rust_misc_device: IOCTLing Rust Misc Device Sample
KERNEL: rust_misc_device: -> Copying data to userspace (value: 1)
USERSPACE: Attempting to call in to an non-existent IOCTL
KERNEL: rust_misc_device: IOCTLing Rust Misc Device Sample
KERNEL: rust_misc_device: -> IOCTL not recognised: 20992
USERSPACE: ioctl: Succeeded to fail - this was expected: Inappropriate ioctl for device
USERSPACE: Closing /dev/rust-misc-device
KERNEL: rust_misc_device: Exiting the Rust Misc Device Sample
USERSPACE: Success

Signed-off-by: Lee Jones <lee@kernel.org>
---
 samples/rust/rust_misc_device.rs | 90 ++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index ae1474a451f1..40ad7266c225 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -4,6 +4,96 @@
 
 //! Rust misc device sample.
 
+/// Below is an example userspace C program that exercises this sample's functionality.
+///
+/// ```c
+/// #include <stdio.h>
+/// #include <stdlib.h>
+/// #include <errno.h>
+/// #include <fcntl.h>
+/// #include <unistd.h>
+/// #include <sys/ioctl.h>
+///
+/// #define RUST_MISC_DEV_FAIL _IO('|', 0)
+/// #define RUST_MISC_DEV_HELLO _IO('|', 0x80)
+/// #define RUST_MISC_DEV_GET_VALUE _IOR('|', 0x81, int)
+/// #define RUST_MISC_DEV_SET_VALUE _IOW('|', 0x82, int)
+///
+/// int main() {
+///   int value, new_value;
+///   int fd, ret;
+///
+///   // Open the device file
+///   printf("Opening /dev/rust-misc-device for reading and writing\n");
+///   fd = open("/dev/rust-misc-device", O_RDWR);
+///   if (fd < 0) {
+///     perror("open");
+///     return errno;
+///   }
+///
+///   // Make call into driver to say "hello"
+///   printf("Calling Hello\n");
+///   ret = ioctl(fd, RUST_MISC_DEV_HELLO, NULL);
+///   if (ret < 0) {
+///     perror("ioctl: Failed to call into Hello");
+///     close(fd);
+///     return errno;
+///   }
+///
+///   // Get initial value
+///   printf("Fetching initial value\n");
+///   ret = ioctl(fd, RUST_MISC_DEV_GET_VALUE, &value);
+///   if (ret < 0) {
+///     perror("ioctl: Failed to fetch the initial value");
+///     close(fd);
+///     return errno;
+///   }
+///
+///   value++;
+///
+///   // Set value to something different
+///   printf("Submitting new value (%d)\n", value);
+///   ret = ioctl(fd, RUST_MISC_DEV_SET_VALUE, &value);
+///   if (ret < 0) {
+///     perror("ioctl: Failed to submit new value");
+///     close(fd);
+///     return errno;
+///   }
+///
+///   // Ensure new value was applied
+///   printf("Fetching new value\n");
+///   ret = ioctl(fd, RUST_MISC_DEV_GET_VALUE, &new_value);
+///   if (ret < 0) {
+///     perror("ioctl: Failed to fetch the new value");
+///     close(fd);
+///     return errno;
+///   }
+///
+///   if (value != new_value) {
+///     printf("Failed: Committed and retrieved values are different (%d - %d)\n", value, new_value);
+///     close(fd);
+///     return -1;
+///   }
+///
+///   // Call the unsuccessful ioctl
+///   printf("Attempting to call in to an non-existent IOCTL\n");
+///   ret = ioctl(fd, RUST_MISC_DEV_FAIL, NULL);
+///   if (ret < 0) {
+///     perror("ioctl: Succeeded to fail - this was expected");
+///   } else {
+///     printf("ioctl: Failed to fail\n");
+///     close(fd);
+///     return -1;
+///   }
+///
+///   // Close the device file
+///   printf("Closing /dev/rust-misc-device\n");
+///   close(fd);
+///
+///   printf("Success\n");
+///   return 0;
+/// }
+/// ```
 use core::pin::Pin;
 
 use kernel::{
-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH v6 0/5] rust: miscdevice: Provide sample driver using the new MiscDevice bindings

[Greg KH]

On Fri, Dec 13, 2024 at 01:47:05PM +0000, Lee Jones wrote:
> This set depends on Alice's most recent MiscDevice changes:
> 
> https://lore.kernel.org/all/20241210-miscdevice-file-param-v3-0-b2a79b666dc5@google.com/
> 
> Changelog v5 -> v6:
>  - pr_info() to dev_info() conversion (based on Alice's new set)
>  - Moved the example C program from the commit message to the file comments
>  - Changed mutex-drop commentary

Much nicer, thanks!  I've applied, and Alice's changes, to my
driver-core-testing branch, let's see what 0-day has to say about
them...

greg k-h

Re: [PATCH v6 2/5] samples: rust: Provide example using the new Rust MiscDevice abstraction

[Danilo Krummrich]

On Fri, Dec 13, 2024 at 01:47:07PM +0000, Lee Jones wrote:
> This sample driver demonstrates the following basic operations:
> 
> * Register a Misc Device
> * Create /dev/rust-misc-device
> * Provide open call-back for the aforementioned character device
> * Operate on the character device via a simple ioctl()
> * Provide close call-back for the character device
> 
> Signed-off-by: Lee Jones <lee@kernel.org>

Reviewed-by: Danilo Krummrich <dakr@kernel.org>

> ---
>  samples/rust/Kconfig             | 10 ++++
>  samples/rust/Makefile            |  1 +
>  samples/rust/rust_misc_device.rs | 87 ++++++++++++++++++++++++++++++++
>  3 files changed, 98 insertions(+)
>  create mode 100644 samples/rust/rust_misc_device.rs
> 
> diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
> index b0f74a81c8f9..df384e679901 100644
> --- a/samples/rust/Kconfig
> +++ b/samples/rust/Kconfig
> @@ -20,6 +20,16 @@ config SAMPLE_RUST_MINIMAL
>  
>  	  If unsure, say N.
>  
> +config SAMPLE_RUST_MISC_DEVICE
> +	tristate "Misc device"
> +	help
> +	  This option builds the Rust misc device.
> +
> +	  To compile this as a module, choose M here:
> +	  the module will be called rust_misc_device.
> +
> +	  If unsure, say N.
> +
>  config SAMPLE_RUST_PRINT
>  	tristate "Printing macros"
>  	help
> diff --git a/samples/rust/Makefile b/samples/rust/Makefile
> index c1a5c1655395..ad4b97a98580 100644
> --- a/samples/rust/Makefile
> +++ b/samples/rust/Makefile
> @@ -2,6 +2,7 @@
>  ccflags-y += -I$(src)				# needed for trace events
>  
>  obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
> +obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
>  obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
>  
>  rust_print-y := rust_print_main.o rust_print_events.o
> diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> new file mode 100644
> index 000000000000..324c3696ae3f
> --- /dev/null
> +++ b/samples/rust/rust_misc_device.rs
> @@ -0,0 +1,87 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Rust misc device sample.
> +
> +use kernel::{
> +    c_str,
> +    device::Device,
> +    fs::File,
> +    ioctl::_IO,
> +    miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
> +    prelude::*,
> +    types::ARef,
> +};
> +
> +const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 0x80);
> +
> +module! {
> +    type: RustMiscDeviceModule,
> +    name: "rust_misc_device",
> +    author: "Lee Jones",
> +    description: "Rust misc device sample",
> +    license: "GPL",
> +}
> +
> +#[pin_data]
> +struct RustMiscDeviceModule {
> +    #[pin]
> +    _miscdev: MiscDeviceRegistration<RustMiscDevice>,
> +}
> +
> +impl kernel::InPlaceModule for RustMiscDeviceModule {
> +    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
> +        pr_info!("Initialising Rust Misc Device Sample\n");
> +
> +        let options = MiscDeviceOptions {
> +            name: c_str!("rust-misc-device"),
> +        };
> +
> +        try_pin_init!(Self {
> +            _miscdev <- MiscDeviceRegistration::register(options),
> +        })
> +    }
> +}
> +
> +struct RustMiscDevice {
> +    dev: ARef<Device>,
> +}
> +
> +#[vtable]
> +impl MiscDevice for RustMiscDevice {
> +    type Ptr = KBox<Self>;
> +
> +    fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<KBox<Self>> {
> +        let dev = ARef::from(misc.device());
> +
> +        dev_info!(dev, "Opening Rust Misc Device Sample\n");
> +
> +        Ok(KBox::new(RustMiscDevice { dev }, GFP_KERNEL)?)
> +    }
> +
> +    fn ioctl(
> +        me: <Self::Ptr as kernel::types::ForeignOwnable>::Borrowed<'_>,
> +        _file: &File,
> +        cmd: u32,
> +        _arg: usize,
> +    ) -> Result<isize> {
> +        dev_info!(me.dev, "IOCTLing Rust Misc Device Sample\n");
> +
> +        match cmd {
> +            RUST_MISC_DEV_HELLO => dev_info!(me.dev, "Hello from the Rust Misc Device\n"),
> +            _ => {
> +                dev_err!(me.dev, "-> IOCTL not recognised: {}\n", cmd);
> +                return Err(ENOTTY);
> +            }
> +        }
> +
> +        Ok(0)
> +    }
> +}
> +
> +impl Drop for RustMiscDevice {
> +    fn drop(&mut self) {
> +        dev_info!(self.dev, "Exiting the Rust Misc Device Sample\n");
> +    }
> +}
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
> 
>