Add redox-os to conditional compilation #[cfg] for ucred usage alongside other linux-like OS

[andrewdavidmackenzie]

I recently got an MR merged into rust libc to add the ucred struct for redox-os.
That was what was missing in order to allow tokio to compile for redox-os.
That change was recently released as part of libc version 0.2.245.

This PR adds the redox-os to the conditional compile directives for the linux-like OSs, so that it can use ucred and compile without any tokio code changes.

This will unblock much useage (and fork and patch maintenance) in redox development for tokio, and allow it to be used much more widely.

It's still WIP as I work on an issue on my end, but wanted to get it here sooner rather than later - hope that is OK.

[Darksonn]

This looks good to me.

Since this is WIP, I will be marking this as a draft. Please remove the draft marker when you think this is ready.

[andrewdavidmackenzie]

I don't understand the rustfmt check error. Is a change required to pass it?

[Darksonn]

Yes, you'll need to reformat the file to pass the check. You can do that by executing rustfmt src/path/to/file. (Note that cargo fmt does not work in our repository, see CONTRIBUTING.md for more info.)

[Darksonn]

Do you know if its possible to run our tests on redox OS in our CI setup?

[andrewdavidmackenzie]

Re: "Do you know if its possible to run our tests on redox OS in our CI setup?"

Thanks for asking!

That is a definite goal for me.

I will ask our BDFL and resident experts to join in here, about how that can be done (I believe using the "redoxer" image on docker, but I am far from an expert on this matter in redox...)

[andrewdavidmackenzie]

AN initial compile check could be done using cargo check --target x86_64-unknown-redox, but to link, you need the redox linker, and probably the redoxer image is the path to do that.

We would really appreciate including that (fairly cheap?) check. Then linking and running correctly (which still requires some work) would be on redox for now. Later, maybe offering you an image as a path to link, run and pass tests on redox.

[andrewdavidmackenzie]

OK, checks passed. Up to you now @Darksonn :-)

[andrewdavidmackenzie]

@Darksonn would you like me to take a shot at a separate PR to add a cargo check check, for redox?

[Darksonn]

Thanks.

[Darksonn]

Yes, if you're able to get a CI check working, then that would be great. We want to avoid breaking platforms once we get them working.

[andrewdavidmackenzie]

I've looked through the ci.yml workflow.
I'm not sure where best to add it....

it's a fairly inexpensive check, but for a platform I wouldn't consider "top tier" yet.
It's just a cargo check (for now) not a full test, so doesn't fit with the tests on matrix.os there.

Add as a new (expensive) step - that runs on ubuntu (for now) and migrate to a redox entry in matrix.os at a later date when we have it running and tests passing?

Thanks for any pointers.

[Darksonn]

If it's possible to run cargo test on Redox via an ubuntu worker, then that sounds like it would be great. As long as it isn't very slow.

[andrewdavidmackenzie]

Not yet.

I am proposing a first step that runs cargo check --target=x86_64-unknown-redox that ensures it all compiles OK (linking is another mater).

[Darksonn]

Okay. Let's do that, then.

[andrewdavidmackenzie]

PR sent #5800 we can continue any related discussion over there.
Thanks for your collaboration!