linux-kernel - Re: [PATCH 3/5] rust: miscdevice: Provide additional abstractions for iov

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Message-ID: <87plicg6th.fsf@kernel.org>
Date: Wed, 19 Mar 2025 20:26:50 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,  "Alexander Viro"
 <viro@...iv.linux.org.uk>,  "Arnd Bergmann" <arnd@...db.de>,  "Miguel
 Ojeda" <ojeda@...nel.org>,  "Boqun Feng" <boqun.feng@...il.com>,  "Gary
 Guo" <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,
  "Benno Lossin" <benno.lossin@...ton.me>,  "Trevor Gross"
 <tmgross@...ch.edu>,  "Danilo Krummrich" <dakr@...nel.org>,  "Matthew
 Maurer" <mmaurer@...gle.com>,  "Lee Jones" <lee@...nel.org>,
  <linux-kernel@...r.kernel.org>,  <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH 3/5] rust: miscdevice: Provide additional abstractions
 for iov_iter and kiocb structures

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> These will be used for the read_iter() and write_iter() callbacks, which
> are now the preferred back-ends for when a user operates on a char device
> with read() and write() respectively.
>
> Co-developed-by: Lee Jones <lee@...nel.org>
> Signed-off-by: Lee Jones <lee@...nel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  rust/kernel/miscdevice.rs | 97 ++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 96 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
> index fa9ecc42602a477328a25b5d357db90b59dc72ae..8daafdc7f3e47aef3c90507082d35ad6819598eb 100644
> --- a/rust/kernel/miscdevice.rs
> +++ b/rust/kernel/miscdevice.rs
> @@ -14,12 +14,13 @@
>      error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
>      ffi::{c_int, c_long, c_uint, c_ulong},
>      fs::File,
> +    iov::{IovIterDest, IovIterSource},
>      prelude::*,
>      seq_file::SeqFile,
>      str::CStr,
>      types::{ForeignOwnable, Opaque},
>  };
> -use core::{marker::PhantomData, mem::MaybeUninit, pin::Pin};
> +use core::{marker::PhantomData, mem::MaybeUninit, pin::Pin, ptr::NonNull};
>
>  /// Options for creating a misc device.
>  #[derive(Copy, Clone)]
> @@ -119,6 +120,16 @@ fn release(device: Self::Ptr, _file: &File) {
>          drop(device);
>      }
>
> +    /// Read from this miscdevice.
> +    fn read_iter(_kiocb: Kiocb<'_, Self::Ptr>, _iov: &mut IovIterDest<'_>) -> Result<usize> {
> +        build_error!(VTABLE_DEFAULT_ERROR)
> +    }
> +
> +    /// Write to this miscdevice.
> +    fn write_iter(_kiocb: Kiocb<'_, Self::Ptr>, _iov: &mut IovIterSource<'_>) -> Result<usize> {
> +        build_error!(VTABLE_DEFAULT_ERROR)
> +    }
> +
>      /// Handler for ioctls.
>      ///
>      /// The `cmd` argument is usually manipulated using the utilties in [`kernel::ioctl`].
> @@ -160,6 +171,36 @@ fn show_fdinfo(
>      }
>  }
>
> +/// Wrapper for the kernel's `struct kiocb`.

Could you give more context? Please describe the purpose for the type
and intended use. Perhaps give an example that can be compile tested.


> +///
> +/// The type `T` represents the private data of the file.
> +pub struct Kiocb<'a, T> {
> +    inner: NonNull<bindings::kiocb>,
> +    _phantom: PhantomData<&'a T>,
> +}

An abstraction for `kiocb` does not belong here. It should go into kernel/fs.


Best regards,
Andreas Hindborg