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

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

On Sun, Jul 20, 2025 at 04:21:00PM -0400, Caleb Sander Mateos wrote:
> 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.

Okay, I'll use same _IO* pattern with ioctl.
> 
> > +
> >  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).

Yes, I've missed this. read_volatile with comment would be good.

Thanks,
Sidong
> 
> 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
> >
> >