linux-kernel - Re: [PATCH v15 2/3] rust: xarray: Add an abstraction for XArray

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Message-ID: <Z6Tu8E4r5ZEolFX1@Mac.home>
Date: Thu, 6 Feb 2025 09:18:40 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Tamir Duberstein <tamird@...il.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...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>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Matthew Wilcox <willy@...radead.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Maíra Canal <mcanal@...lia.com>,
	Asahi Lina <lina@...hilina.net>, rust-for-linux@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH v15 2/3] rust: xarray: Add an abstraction for XArray

Hi Tamir,

This looks good to me overall, a few comments below:

On Thu, Feb 06, 2025 at 11:24:44AM -0500, Tamir Duberstein wrote:
[...]
> +impl<'a, T: ForeignOwnable> Guard<'a, T> {
[...]
> +    /// Loads an entry from the array.
> +    ///
> +    /// Returns the entry at the given index.
> +    pub fn get(&self, index: usize) -> Option<T::Borrowed<'_>> {
> +        self.load(index, |ptr| {
> +            // SAFETY: `ptr` came from `T::into_foreign`.
> +            unsafe { T::borrow(ptr.as_ptr()) }
> +        })
> +    }
> +
> +    /// Loads an entry from the array.

Nit: firstly, this function has the same description of `get()`, also
I would prefer something like "Returns a [`T::Borrowed`] of the object
at `index`" rather then "Loads an entry from the array", thoughts?

> +    ///
> +    /// Returns the entry at the given index.
> +    pub fn get_mut(&mut self, index: usize) -> Option<T::BorrowedMut<'_>> {
> +        self.load(index, |ptr| {
> +            // SAFETY: `ptr` came from `T::into_foreign`.
> +            unsafe { T::borrow_mut(ptr.as_ptr()) }
> +        })
> +    }
> +
> +    /// Erases an entry from the array.

Nit: s/Erases/Removes?

> +    ///
> +    /// Returns the entry which was previously at the given index.
> +    pub fn remove(&mut self, index: usize) -> Option<T> {
> +        // SAFETY: `self.xa.xa` is always valid by the type invariant.
> +        //
> +        // SAFETY: The caller holds the lock.
> +        let ptr = unsafe { bindings::__xa_erase(self.xa.xa.get(), index) }.cast();
> +        // SAFETY: `ptr` is either NULL or came from `T::into_foreign`.

SAFETY comment here needs to mention why there is no alive `T::Borrowed`
or `T::BorrowedMut` out there per the safety requirement.

Regards,
Boqun

> +        unsafe { T::try_from_foreign(ptr) }
> +    }
> +
[...]