[RFC PATCH v3 5/5] samples: rust: Add `uring_cmd` example to `rust_misc_device`

[Sidong Yang <sidong.yang@furiosa.ai>]

This patch extends the `rust_misc_device` sample to demonstrate how to
use the `uring_cmd` interface for asynchronous device operations.

The new implementation handles two `uring_cmd` operations:

*   `RUST_MISC_DEV_URING_CMD_SET_VALUE`: Sets a value in the device.
*   `RUST_MISC_DEV_URING_CMD_GET_VALUE`: Gets a value from the device.

To use this new functionality, users can submit `IORING_OP_URING_CMD`
operations to the `rust_misc_device` character device.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
---
 samples/rust/rust_misc_device.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index e7ab77448f75..1f25d2b1f4d8 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -101,6 +101,7 @@
     c_str,
     device::Device,
     fs::File,
+    io_uring::IoUringCmd,
     ioctl::{_IO, _IOC_SIZE, _IOR, _IOW},
     miscdevice::{MiscDevice, MiscDeviceOptions, MiscDeviceRegistration},
     new_mutex,
@@ -114,6 +115,9 @@
 const RUST_MISC_DEV_GET_VALUE: u32 = _IOR::<i32>('|' as u32, 0x81);
 const RUST_MISC_DEV_SET_VALUE: u32 = _IOW::<i32>('|' as u32, 0x82);
 
+const RUST_MISC_DEV_URING_CMD_SET_VALUE: u32 = _IOR::<i32>('|' as u32, 0x83);
+const RUST_MISC_DEV_URING_CMD_GET_VALUE: u32 = _IOW::<i32>('|' as u32, 0x84);
+
 module! {
     type: RustMiscDeviceModule,
     name: "rust_misc_device",
@@ -192,6 +196,29 @@ fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result
 
         Ok(0)
     }
+
+    fn uring_cmd(
+        me: Pin<&RustMiscDevice>,
+        io_uring_cmd: Pin<&mut IoUringCmd>,
+        _issue_flags: u32,
+    ) -> Result<i32> {
+        dev_info!(me.dev, "UringCmd Rust Misc Device Sample\n");
+
+        let cmd = io_uring_cmd.cmd_op();
+        let addr: usize = io_uring_cmd.sqe().cmd_data()?;
+        let user_ptr = UserPtr::from_addr(addr);
+        let user_slice = UserSlice::new(user_ptr, 8);
+
+        match cmd {
+            RUST_MISC_DEV_URING_CMD_SET_VALUE => me.set_value(user_slice.reader())?,
+            RUST_MISC_DEV_URING_CMD_GET_VALUE => me.get_value(user_slice.writer())?,
+            _ => {
+                dev_err!(me.dev, "-> uring_cmd not recognised: {}\n", cmd);
+                return Err(ENOTTY);
+            }
+        };
+        Ok(0)
+    }
 }
 
 #[pinned_drop]
-- 
2.43.0