Re: [RFC PATCH 0/7] Rust Socket abstractions

[Miguel Ojeda]

On Thu, Aug 17, 2023 at 4:53 PM Michele Dalle Rive
<dallerivemichele@xxxxxxxxx> wrote:
>
> The idea behind this patch is that, as of now, Rust is not a viable option for
> any OOT module that requires even the highest-level network support.
>
> I am wondering whether the `net` subsystem is interested in reviewing, giving
> feedback and eventually accepting code that is currently OOT-only.

It is unlikely kernel maintainers in general accept code intended for
out-of-tree modules only.

To be clear, Rust for Linux's focus has never been out-of-tree
modules. In fact, the whole effort since the beginning was about
adding support for Rust in-tree, unlike other projects that e.g.
linked `rustc`-built object files into an out-of-tree kernel module.

We do support out-of-tree modules, and have a sample of that, but that
is just only to the degree that the kernel supports out-of-tree
modules in general.

The abstractions that have been upstreamed so far are those that have
(or should soon have) a user in-tree. Sometimes we have had to bend a
bit the rules in order to split the dependency chain or make things
easier, but abstractions (in general) cannot be upstreamed that do not
have at least an expected and public user that is going upstream too.
Here, by user, we generally mean an actual driver or useful component
(rather than a sample).

If I understood correctly from Zulip, you cannot (right now) show your
use case because it is confidential and therefore you cannot upstream
it, so we will need another user (and, of course, that is a necessary
but not sufficient condition for the code to be accepted).

> Also, it would be interesting if you could provide us any module or
> functionality you are planning to get in-tree which might use this interface;
> it could be useful in order to understand the applicability of these
> abstractions and find a concrete in-kernel use-case.

I think it is easier if it is the other way around :) That is, the
people/companies that already have a use case for the abstractions
should come forward and publish them so that the abstractions are
justified.

Of course, this does not preclude discussing about them or having a
`rust-net` branch or sub-subsystem or similar. That could be quite
useful so develop those users and to experiment. In fact, we are
actively trying to onboard more people (and companies and other
entities) to the Rust overall kernel effort, so please feel free to
join us.

> I included in the email a couple of sample OOT modules that showcase the
> functionalities of the socket API; they will be attached as an actual patch if
> there will be a v2.

The sample should not be an out-of-tree module, it should be an
in-tree one. However, for upstreaming, just a sample is likely to not
be enough for most kernel maintainers, as mentioned above.

By the way, I am a bit confused -- the patch seems to add an in-tree
sample, not an out-of-tree one.

Cheers,
Miguel