linux-kernel - Re: [PATCH 3/4] rust: miscdevice: add uring

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Message-ID: <CADUfDZpmD-WfVsrzNOt6T6132M+EHCGtRcnQH7p0z2f3f6dBvw@mail.gmail.com>
Date: Sun, 20 Jul 2025 16:08:19 -0400
From: Caleb Sander Mateos <csander@...estorage.com>
To: Sidong Yang <sidong.yang@...iosa.ai>
Cc: Miguel Ojeda <ojeda@...nel.org>, Arnd Bergmann <arnd@...db.de>, Jens Axboe <axboe@...nel.dk>, 
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
	io-uring@...r.kernel.org
Subject: Re: [PATCH 3/4] rust: miscdevice: add uring_cmd() for MiscDevice trait

On Sat, Jul 19, 2025 at 10:35 AM Sidong Yang <sidong.yang@...iosa.ai> wrote:
>
> This patch adds uring_cmd() function for MiscDevice trait and its
> callback implementation. It uses IoUringCmd that io_uring_cmd rust
> abstraction.
>
> Signed-off-by: Sidong Yang <sidong.yang@...iosa.ai>
> ---
>  rust/kernel/miscdevice.rs | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
> index 288f40e79906..5255faf27934 100644
> --- a/rust/kernel/miscdevice.rs
> +++ b/rust/kernel/miscdevice.rs
> @@ -14,6 +14,7 @@
>      error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
>      ffi::{c_int, c_long, c_uint, c_ulong},
>      fs::File,
> +    io_uring::IoUringCmd,
>      mm::virt::VmaNew,
>      prelude::*,
>      seq_file::SeqFile,
> @@ -175,6 +176,15 @@ fn show_fdinfo(
>      ) {
>          build_error!(VTABLE_DEFAULT_ERROR)
>      }
> +
> +    fn uring_cmd(
> +        _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
> +        _file: &File,
> +        _io_uring_cmd: &IoUringCmd,
> +        issue_flags: u32,
> +    ) -> Result<isize> {

Would i32 make more sense as the return value, since that's what
io_uring_cqe actually stores?

> +        build_error!(VTABLE_DEFAULT_ERROR)
> +    }
>  }
>
>  /// A vtable for the file operations of a Rust miscdevice.
> @@ -332,6 +342,25 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
>          T::show_fdinfo(device, m, file);
>      }
>
> +    unsafe extern "C" fn uring_cmd(
> +        ioucmd: *mut bindings::io_uring_cmd,
> +        issue_flags: ffi::c_uint,
> +    ) -> ffi::c_int {
> +        // SAFETY: The file is valid for the duration of this call.
> +        let ioucmd = unsafe { IoUringCmd::from_raw(ioucmd) };
> +        let file = ioucmd.file();
> +
> +        // SAFETY: The file is valid for the duration of this call.
> +        let private = unsafe { (*file.as_ptr()).private_data }.cast();
> +        // SAFETY: Ioctl calls can borrow the private data of the file.

"Ioctl" -> "uring cmd"?

Best,
Caleb

> +        let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
> +
> +        match T::uring_cmd(device, file, ioucmd, issue_flags) {
> +            Ok(ret) => ret as ffi::c_int,
> +            Err(err) => err.to_errno() as ffi::c_int,
> +        }
> +    }
> +
>      const VTABLE: bindings::file_operations = bindings::file_operations {
>          open: Some(Self::open),
>          release: Some(Self::release),
> @@ -354,6 +383,11 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
>          } else {
>              None
>          },
> +        uring_cmd: if T::HAS_URING_CMD {
> +            Some(Self::uring_cmd)
> +        } else {
> +            None
> +        },
>          // SAFETY: All zeros is a valid value for `bindings::file_operations`.
>          ..unsafe { MaybeUninit::zeroed().assume_init() }
>      };
> --
> 2.43.0
>
>