Re: [PATCH v6 4/6] rust: xarray: Add support for index reservations

[Philipp Stanner]

On Wed, 2026-08-05 at 10:50 +0200, Andreas Hindborg wrote:
> "Philipp Stanner" <phasta@xxxxxxxxxx> writes:
> 
> > One often cannot allocate in the kernel with the desired flags, most
> > notably in atomic context. Pre-allocating the memory is the preferred
> > solution in such situations.
> > 
> > Add support for xa_reserve() in the Rust abstractions of xarray. Create
> > a Reservation object similar to a lock-guard, that can be dropped once
> > the reservation is no longer needed or once the index was stored to.
> > 
> > Signed-off-by: Philipp Stanner <phasta@xxxxxxxxxx>
> > ---
> > Please regard this more as an RFC.
> > 
> > I need pre-allocating in XArray for DmaFence. How exactly we achieve
> > this is open for discussion.
> 
> Do you need to actually reserve a key, or do you just need atomic
> allocation?

I would just have needed a position to store to, but the fence sequence
number would be the only reasonable index, so you'd also reserve a key.



Anyways, please forget about this for now, we abstained from using the
XArray in the current revision (v8) of this patch series.


Thx
P.