linux-kernel - Re: [PATCH v3 1/3] rust: miscdevice: access file in fops

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Message-ID: <20241211115651.GB7139@google.com>
Date: Wed, 11 Dec 2024 11:56:51 +0000
From: Lee Jones <lee@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] rust: miscdevice: access file in fops

On Tue, 10 Dec 2024, Alice Ryhl wrote:

> This allows fops to access information about the underlying struct file
> for the miscdevice. For example, the Binder driver needs to inspect the
> O_NONBLOCK flag inside the fops->ioctl() hook.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  rust/kernel/miscdevice.rs | 31 +++++++++++++++++++++++++------
>  1 file changed, 25 insertions(+), 6 deletions(-)

Reviewed-by: Lee Jones <lee@...nel.org>

> diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
> index 7e2a79b3ae26..0cb79676c139 100644
> --- a/rust/kernel/miscdevice.rs
> +++ b/rust/kernel/miscdevice.rs
> @@ -11,6 +11,7 @@
>  use crate::{
>      bindings,
>      error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
> +    fs::File,
>      prelude::*,
>      str::CStr,
>      types::{ForeignOwnable, Opaque},
> @@ -103,10 +104,10 @@ pub trait MiscDevice {
>      /// Called when the misc device is opened.
>      ///
>      /// The returned pointer will be stored as the private data for the file.
> -    fn open() -> Result<Self::Ptr>;
> +    fn open(_file: &File) -> Result<Self::Ptr>;
>  
>      /// Called when the misc device is released.
> -    fn release(device: Self::Ptr) {
> +    fn release(device: Self::Ptr, _file: &File) {
>          drop(device);
>      }
>  
> @@ -117,6 +118,7 @@ fn release(device: Self::Ptr) {
>      /// [`kernel::ioctl`]: mod@...te::ioctl
>      fn ioctl(
>          _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
> +        _file: &File,
>          _cmd: u32,
>          _arg: usize,
>      ) -> Result<isize> {
> @@ -133,6 +135,7 @@ fn ioctl(
>      #[cfg(CONFIG_COMPAT)]
>      fn compat_ioctl(
>          _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
> +        _file: &File,
>          _cmd: u32,
>          _arg: usize,
>      ) -> Result<isize> {
> @@ -187,7 +190,10 @@ impl<T: MiscDevice> VtableHelper<T> {
>          return ret;
>      }
>  
> -    let ptr = match T::open() {
> +    // SAFETY:
> +    // * The file is valid for the duration of this call.
> +    // * There is no active fdget_pos region on the file on this thread.
> +    let ptr = match T::open(unsafe { File::from_raw_file(file) }) {
>          Ok(ptr) => ptr,
>          Err(err) => return err.to_errno(),
>      };
> @@ -211,7 +217,10 @@ impl<T: MiscDevice> VtableHelper<T> {
>      // SAFETY: The release call of a file owns the private data.
>      let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private) };
>  
> -    T::release(ptr);
> +    // SAFETY:
> +    // * The file is valid for the duration of this call.
> +    // * There is no active fdget_pos region on the file on this thread.
> +    T::release(ptr, unsafe { File::from_raw_file(file) });
>  
>      0
>  }
> @@ -229,7 +238,12 @@ impl<T: MiscDevice> VtableHelper<T> {
>      // SAFETY: Ioctl calls can borrow the private data of the file.
>      let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
>  
> -    match T::ioctl(device, cmd, arg as usize) {
> +    // SAFETY:
> +    // * The file is valid for the duration of this call.
> +    // * There is no active fdget_pos region on the file on this thread.
> +    let file = unsafe { File::from_raw_file(file) };
> +
> +    match T::ioctl(device, file, cmd, arg as usize) {
>          Ok(ret) => ret as c_long,
>          Err(err) => err.to_errno() as c_long,
>      }
> @@ -249,7 +263,12 @@ impl<T: MiscDevice> VtableHelper<T> {
>      // SAFETY: Ioctl calls can borrow the private data of the file.
>      let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
>  
> -    match T::compat_ioctl(device, cmd, arg as usize) {
> +    // SAFETY:
> +    // * The file is valid for the duration of this call.
> +    // * There is no active fdget_pos region on the file on this thread.
> +    let file = unsafe { File::from_raw_file(file) };
> +
> +    match T::compat_ioctl(device, file, cmd, arg as usize) {
>          Ok(ret) => ret as c_long,
>          Err(err) => err.to_errno() as c_long,
>      }
> 
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
> 

-- 
Lee Jones [李琼斯]