Re: Rust BoF and maintainer minutes and planning the roadmap to Rust

["Alex Bennée" <alex.bennee@linaro.org>]

Stefan Hajnoczi <stefanha@gmail.com> writes:

> On Thu, 26 Sept 2024 at 10:24, Alex Bennée <alex.bennee@linaro.org> wrote:
<snip>
>> Another potential area for conversion was the VirtIO device and
>> vhost-user code which could expect to re-use a lot of the crates from
>> the rust-vmm project. However this did bring up the point of maintainer
>> buy in. Stefan brought up the example of the simpletrace rewrite which
>> while it may have brought some advantages he felt he was unable to take
>> as a maintainer as he was not familiar with Rust at that point.
>
> Familiarity with Rust was not the issue with simpletrace. I had
> already worked on libblkio in Rust and was able to understand the Rust
> simpletrace patches.

Apologies for misrepresenting the issue there. My notes obviously didn't
capture that nuance. 

> It was a question of when rewriting in Rust is appropriate. Surprising
> maintainers with a rewrite is risky because they may not be convinced
> by the rewrite after all the work to write it has been done.
>
> In the case of simpletrace there wasn't a clear benefit to a rewrite:
> performance was potentially better in Rust (performance hadn't been a
> problem for users though) but usability was impacted by converting a
> scriptable Python module to Rust (requiring users to rewrite their
> scripts). The rewrite was dropped.
>
> What I tried to express at the Rust BoF was: talk to maintainers
> before embarking on a rewrite.

Yes this is the I think the key takeaway because the project would not
be able to absorb a bunch of drive-by rust rewrites from well meaning
contributors.

>> With relative inexperience there was a concern we could inadvertently
>> introduce technical debt in the code base (C-like Rust vs Rusty rust).
>> What can we do to mitigate that issue?
>
> My suggestion is that every `unsafe` needs a comment explaining why it
> is safe. That increases the cost of using `unsafe` and encourages safe
> abstractions.
>
> There are plenty of unidiomatic ways of using Rust, but none are as
> bad as sprinkling `unsafe` everywhere (i.e. writing C in Rust) since
> that's how undefined behavior is introduced.
>
> Stefan

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro