Re: [PATCH v2] rust: rbtree: add immutable cursor

["Alexandre Courbot" <acourbot@nvidia.com>]

On Thu Sep 11, 2025 at 4:40 AM JST, John Hubbard wrote:
> On 9/9/25 7:50 PM, Miguel Ojeda wrote:
>> On Wed, Sep 10, 2025 at 3:09 AM John Hubbard <jhubbard@nvidia.com> wrote:
>>>
>>> Interesting. I know the topic of rustc minimum version (1.78 right now)
>>> has been discussed a lot, but I'm somehow still confused about how this
>>> works, on nova for example.
>>>
>>> The &raw feature requires rustc 1.82.0. So I thought we couldn't use
>>> it. But clearly we can...right?
>>>
>>> So confused. Please help. :)
>> 
>> Please see what I have at this subpage:
>> 
>>      https://rust-for-linux.com/unstable-features
>> 
>> I hope that helps!
>> 
>
> Hi Miguel!
>
> It leaves unanswered, the question of whether (and how) to use something
> like the &raw feature, which requires Rust 1.82.0, given that the
> stated min Rust version is 1.78.
>
> Is there some sort of exception to the "min Rust version"? I haven't
> figured out where that is written down.

My understanding is that while the feature enabling this syntax
(`raw_ref_op`) is stable since 1.82, it has been introduced as an
unstable feature before 1.78. So it is here, just not enabled by
default before 1.82.

R4L enables some of these unstable features when needed, especially
since they have been stabilized meanwhile. For instance, we did it with
the `pointer_is_aligned` feature for the `FromBytes` patch [1].

[1] https://lore.kernel.org/rust-for-linux/20250824213134.27079-1-christiansantoslima21@gmail.com/#iZ31rust:kernel:lib.rs