docker: Add Nix Store volume support

[otavio]

When running inside NixOS or using Nix packaging we need to add the Nix
Store to the running container so it can load the needed binaries.

Signed-off-by: Otavio Salvador [email protected]

[otavio]

The error on the pipeline does not seem related. Any idea what might have caused it?

[otavio]

The error on the pipeline does not seem related. Any idea what might have caused it?

This is indeed not related. See:

E: Unable to locate package linux-image-4.19.0-11-arm64:arm64
E: Couldn't find any package by glob 'linux-image-4.19.0-11-arm64'
E: Couldn't find any package by regex 'linux-image-4.19.0-11-arm64'

[otavio]

Any news on this?

[reitermarkus]

What is the use case for this? It seems like this should already be possible using env.volumes.

[otavio]

It fails to run automatically; so we would need to pass it to every time we call cross when using NixOS.

[reitermarkus]

It fails to run automatically

What exactly fails to run? I'm not really familiar with NixOS, can you explain in more detail which packages need to be available/mounted in the container and why?

[otavio]

I am unsure if you know what NixOS is. So please take a look at How Nix works document. It explains how the Nix store works and more.

In summary, without the patch, cross fails to run because it cannot find the binaries it runs inside the container. It took me a while to understand the root cause of the error but now it works just fine. This is the same patch I apply in the official Nix package.

[reitermarkus]

It explains how the Nix store works and more.

Okay, I understand now what the Nix store is/does.

it cannot find the binaries it runs inside the container

I'm still not sure what specifically the problem is though. Let me know if the following assumption is correct.

Let's say we are talking about the cargo binary:

• We mount the rustup toolchain into the container.
• The toolchain's ./bin/cargo is not a binary but a symlink into the Nix store.
• Calling cargo fails since the Nix store is not mounted.

[otavio]

Exactly, your understanding is correct. Doing the mount inside the container allows it to run successfully.

[reitermarkus]

Just one more question. Does Nix use some kind of customized version of rustup or how does symlinking the toolchain bineries into Nix store happen? I'd assume rustup just installs a complete pre-built toolchain from a tarball. Or is this a custom toolchain installed by Nix and not rustup?

[otavio]

Yes, it does. See rustup.

[reitermarkus]

bors r+

[bors]

Build failed:

• conclusion

[otavio]

Should I do anything on my side on this one?

[Emilgardis]

fix the fmt error and it should be good to go :)

https://github.com/cross-rs/cross/runs/5578287402?check_suite_focus=true#step:4:10

bors d+

edit:: Actually, delegation doesn't work well when new commits dismisses reviews :/

[bors]

✌️ otavio can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[otavio]

bors r+

[bors]

👎 Rejected by too few approved reviews

[Emilgardis]

yeah, thought so. Should maybe fix that in upstream bors (or disable dismissal)

[Emilgardis]

bors r+

[bors]

Build succeeded:

• conclusion

[Emilgardis]

I think there was an issue for this, this should pr should close that