linux-kernel - Re: [PATCH v2 2/4] rust: xarray: abstract `xa

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Message-ID: <CAJ-ks9mtfVmP+SwZvBVuQSwViiqo2ZngSGQuU5Y7A-Q_JSwjKQ@mail.gmail.com>
Date: Wed, 8 Oct 2025 09:59:12 -0700
From: Tamir Duberstein <tamird@...il.com>
To: Onur Özkan <work@...rozkan.dev>
Cc: rust-for-linux@...r.kernel.org, ojeda@...nel.org, alex.gaynor@...il.com, 
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, 
	lossin@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu, dakr@...nel.org, 
	linux-kernel@...r.kernel.org, acourbot@...dia.com, airlied@...il.com, 
	simona@...ll.ch, maarten.lankhorst@...ux.intel.com, mripard@...nel.org, 
	tzimmermann@...e.de, corbet@....net, lyude@...hat.com, 
	linux-doc@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/4] rust: xarray: abstract `xa_alloc`

On Wed, Oct 8, 2025 at 6:05 AM Onur Özkan <work@...rozkan.dev> wrote:
>
> Implements `alloc` function to `XArray<T>` that wraps
> `xa_alloc` safely, which will be used to generate the
> auxiliary device IDs.
>
> Resolves a task from the nova/core task list under the "XArray
> bindings [XARR]" section in "Documentation/gpu/nova/core/todo.rst"
> file.
>
> Signed-off-by: Onur Özkan <work@...rozkan.dev>
> ---
>  rust/kernel/xarray.rs | 41 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/xarray.rs b/rust/kernel/xarray.rs
> index 90e27cd5197e..0711ccf99fb4 100644
> --- a/rust/kernel/xarray.rs
> +++ b/rust/kernel/xarray.rs
> @@ -10,7 +10,7 @@
>      ffi::c_void,
>      types::{ForeignOwnable, NotThreadSafe, Opaque},
>  };
> -use core::{iter, marker::PhantomData, pin::Pin, ptr::NonNull};
> +use core::{iter, marker::PhantomData, ops::Range, pin::Pin, ptr::NonNull};
>  use pin_init::{pin_data, pin_init, pinned_drop, PinInit};
>
>  /// An array which efficiently maps sparse integer indices to owned objects.
> @@ -268,6 +268,45 @@ pub fn store(
>              Ok(unsafe { T::try_from_foreign(old) })
>          }
>      }
> +
> +    /// Allocates an empty slot within the given `limit` and stores `value` there.
> +    ///
> +    /// May drop the lock if needed to allocate memory, and then reacquire it afterwards.
> +    ///
> +    /// On success, returns the allocated index.

Returning the index is not a very good abstraction. Would the
reservation API meet your needs?

https://lore.kernel.org/all/20250713-xarray-insert-reserve-v2-3-b939645808a2@gmail.com/

If yes, I would appreciate your tags there.