[RFC PATCH v2 4/4] samples: rust: rust_misc_device: add uring_cmd example

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

This patch makes rust_misc_device handle uring_cmd. Command ops are like
ioctl that set or get values in simple way.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
---
 samples/rust/rust_misc_device.rs | 34 ++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index c881fd6dbd08..1044bde86e8d 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",
@@ -190,6 +194,36 @@ 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 cmd_data = io_uring_cmd.sqe().cmd_data().as_ptr() as *const usize;
+
+        // SAFETY: `cmd_data` is guaranteed to be a valid pointer to the command data
+        // within the SQE structure.
+        // FIXME: switch to read_once() when it's available.
+        let addr = unsafe { core::ptr::read_volatile(cmd_data) };
+
+        match cmd {
+            RUST_MISC_DEV_URING_CMD_SET_VALUE => {
+                me.set_value(UserSlice::new(addr, 8).reader())?;
+            }
+            RUST_MISC_DEV_URING_CMD_GET_VALUE => {
+                me.get_value(UserSlice::new(addr, 8).writer())?;
+            }
+            _ => {
+                dev_err!(me.dev, "-> uring_cmd not recognised: {}\n", cmd);
+                return Err(ENOTTY);
+            }
+        }
+        Ok(0)
+    }
 }
 
 #[pinned_drop]
-- 
2.43.0