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

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Message-ID: <8734f8g4is.fsf@kernel.org>
Date: Wed, 19 Mar 2025 21:16:27 +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>

[...]

> +impl<'a, T: ForeignOwnable> Kiocb<'a, T> {
> +    /// Get the private data in this kiocb.
> +    pub fn private_data(&self) -> <T as ForeignOwnable>::Borrowed<'a> {
> +        // SAFETY: The `kiocb` lets us access the private data.
> +        let private = unsafe { (*(*self.inner.as_ptr()).ki_filp).private_data };
> +        // SAFETY: The kiocb has shared access to the private data.
> +        unsafe { <T as ForeignOwnable>::borrow(private) }
> +    }

Another quick observation: `kiocb` has a `void *private` field that is
used in the same way that `struct file` `private_data` field is used.
The naming of this function is misleading, since it does not return the
`kiocb` private data.

Either rename this function or exchange it for an access method for the
associated file.


Best regards,
Andreas Hindborg