linux-kernel - Re: [PATCH 00/17] Rust support

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Date:   Wed, 7 Jul 2021 15:07:50 +0100
From:   Wedson Almeida Filho <wedsonaf@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        rust-for-linux <rust-for-linux@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/17] Rust support

On Wed, Jul 07, 2021 at 02:50:54PM +0200, Greg Kroah-Hartman wrote:
> On Wed, Jul 07, 2021 at 02:33:57PM +0200, Miguel Ojeda wrote:
> > Now, if you are OK with non-hardware modules, you can take a look at
> > Rust Binder (last patch in the series) which is a non-trivial module
> > and it is already working.
> 
> Cool, does it actually pass the binder self-tests that the Android
> systems have for the codebase?

We haven't run the Android tests yet because they depend on an Android-specific
service (servicemanager) running and other Android-specific libraries. What we
are doing instead is adding binder tests that don't depend on anything
Android-specific; in fact, we are putting them in tools/testing/selftests/binder
so that they can run on any vanilla system.

The commit is available here:
https://github.com/wedsonaf/linux/commit/f90ec49be9207fa765f07ad1071210ad871712ac

The tests are written in C and run successfully against both C and Rust drivers.
I still have another ~20 tests that I wrote in another harness that I will
convert to selftests soon, but the two together I believe have more coverage
than the ones in Android.

We also have a trivial latency benchmark (ping with no payload) where the Rust
version performs better than the C one.

The benchmark is available here: https://github.com/wedsonaf/linux/commits/ping

> Last I looked at this thing, it was not
> feature-complete compared to the in-kernel binder code, has that been
> resolved and the needed filesystem changes added?

It is not feature-complete in comparison to the C one just yet, it is missing a
few things but not for any fundamental reason -- we were mostly focusing on the
kernel crate and tests.

Miguel's point is that it does implement the vast majority of binder features
and is non-trivial, so it could be used as evidence that useful kernel drivers
can be built with Rust; not just "transpiled" from C, but written with the Rust
safety guarantees.

Cheers,
-Wedson