I could use some advice on the miri error. It looks like perhaps the miri test environment does not support the memfd syscall, which is used in the Rust DNS module and thus the DNS test cases. I'm wondering if this is a valid case where we should turn off the miri test for the DNS unit tests, and if so how to do that.

Looks like we could ignore a test in miri with #[cfg_attr(miri, ignore)], but still not sure if it is valid to do so in this case.

I could use some advice on the miri error. It looks like perhaps the miri test environment does not support the memfd syscall, which is used in the Rust DNS module and thus the DNS test cases. I'm wondering if this is a valid case where we should turn off the miri test for the DNS unit tests, and if so how to do that.

Looks like we could ignore a test in miri with #[cfg_attr(miri, ignore)], but still not sure if it is valid to do so in this case.

I think there are two equally fine options:

1. Since the new rust code is not using any unsafe (within shadow's code at least), it's fine to skip miri tests with #[cfg_attr(miri, ignore)]. In theory since the test only uses the new code and none of the new code uses unsafe, miri shouldn't be needed.

2. It's not bad to test with miri anyways. Instead of disabling the test under miri, you could modify DnsBuilder::into_dns to do something like:

#[cfg(not(miri))]
let mut file = File::from(rustix::fs::memfd_create(name, MemfdFlags::CLOEXEC)?);
#[cfg(miri)]
let mut file = tempfile::tempfile().unwrap();

It seems like miri is getting stuck due to the "/proc/pid/fd/X" :( Here's a playground link that shows miri not working with the "/proc/self/fd/{}" line, but working if you just reuse the original file:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=2274b85d39a3b2925618e371c84b1ebe

I'm guessing that since miri does it's own virtualized file descriptors, it just doesn't support these paths.

The only thing I can think to do instead is to try using a NamedTempFile, using NamedTempFile::keep, using the returned path for hosts_path, and then adding a drop handler to Dns which deletes the file with that path if miri is being used.