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

[Caleb Sander Mateos <csander@purestorage.com>]

On Sat, Jul 19, 2025 at 10:35 AM Sidong Yang <sidong.yang@furiosa.ai> wrote:
>
> 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 | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
>
> diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> index c881fd6dbd08..cd0e578231d2 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 = 0x83;
> +const RUST_MISC_DEV_URING_CMD_GET_VALUE: u32 = 0x84;

In real uring_cmd() implementations, the cmd_op values are assigned
using the _IO* macros, same as for ioctls. But I suppose that's not
strictly required for the sample driver.

> +
>  module! {
>      type: RustMiscDeviceModule,
>      name: "rust_misc_device",
> @@ -190,6 +194,32 @@ fn ioctl(me: Pin<&RustMiscDevice>, _file: &File, cmd: u32, arg: usize) -> Result
>
>          Ok(0)
>      }
> +
> +    fn uring_cmd(
> +        me: Pin<&RustMiscDevice>,
> +        _file: &File,
> +        io_uring_cmd: &IoUringCmd,
> +        _issue_flags: u32,
> +    ) -> Result<isize> {
> +        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;
> +        let addr = unsafe { *cmd_data };

The io_uring_sqe is user-mapped memory, so this load needs to be
atomic. In C, the uring_cmd() implementation would use READ_ONCE().
Sounds like Rust code is currently using read_volatile() (with a FIXME
comment to switch to read_once() once that's available).

Best,
Caleb

> +
> +        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
>
>