fix(uhyve): fix improper unlink string handling

[n0toose]

Taken from traverse_open.

[n0toose]

I caught this as I was working on benchmarks for Uhyve. Using a modified test of Uhyve, this seems to be working. There was an error when converting a char pointer to an str because it was not in UTF-8 - which is a check that I built into Uhyve to prevent weird behavior like this. This means that fs::remove_file has been broken on Uhyve for a while now - but I did not catch that, as I tested the call on my host system without a UhyveVm under the assumption that it previously did.

Anyways, this is not the case anymore. CC: @jounathaen

[0][INFO] Try to initialize uhyve filesystem
[0][INFO] Mounting uhyve filesystem at /root
[0][INFO] Jumping into application
Hello from create_file!
Successfully removed file!
Number of interrupts
[0][FPU]: 1

[n0toose]

Here's the code to reproduce, @mkroening:

use std::{fs::File, io::prelude::*, fs::remove_file};

#[cfg(target_os = "hermit")]
use hermit as _;

fn main() {
	println!("Hello from create_file!");

	let mut file = File::create("/root/foo.txt").unwrap();
	file.write_all(b"Hello, world!").unwrap();
        // this is what I added to the test myself
	remove_file("/root/foo.txt").unwrap();
	println!("Successfully removed file!");
}

Seems like this "bug" was caused by the following commit: ba9f92c

... which took some extra steps to ensure that null terminators were handled properly in traverse_open but were perhaps forgotten about in traverse_unlink, which was unused at the time. The unlink call at the time accepted any path on the host OS and was / is not 'mount-aware' the same way open is.