nixos-rebuild build-vm - fails with "waiting for device to appear"

[vacy]

Hello,

thank you for the effort on the module, much appreciated!
I am fairly new to nixOS, just started a month ago and from the very beginning I wanted to setup my systems with impermanence - and now I am about to get it done - sooo close!

Now I

1. took my testsystems hardwareconfig and modified the mounts
2. added the impermanence module + config to the flake
3. ran nixos-rebuild --flake .#testvm build-vm

It builds the vm perfectly fine, but the boot fails in stage1 since its

"waiting for device /mnt-root/nix/persist/system/var/lib/nixos to appear"

and fails into:

"nixos failed: No such file or directory"

I dont know where the "mnt-root" comes from, I dont find it in my own config nor in your codebase here on github, so I am guessing thats coming from nixOS itself?
You'll see some mntroot mounts in my config, that is me stumbling around with that error message, I tried to align my config with the error message and had configured to mount to /mnt-root in the beginning.
But changed back to /mntroot later on.

[root@nixtop:/etc/nixos/flakes]# grep -r mnt-root
grep: vm.qcow2: binary file matches

So I figured the /nix/persist/system does not exist on a new system, I did some research and guess your #193 sounds promising.
But I am running on your master branch, so I wont know how to continue.

Ive tried to workaround that problem in the flake with:

systemd.tmpfiles.rules = [
"d /nix/persist/ 0755 root root"
"d /nix/persist/system 0755 root root"
];

Doesnt matter, it ends up in the same problem.
So my best guess is: build-vm is out of scope for your project?
Oh headsup, I am still on 24.05
edit:/ changed my flake inputs to 24.11 and came up with the same problem. sitenote: nix is great for being that quick making such changes :)

Config details:

flake

environment.persistence."/nix/persist/system" = {
hideMounts = true;
directories = [
"/var/log"
"/var/lib/bluetooth"
"/var/lib/nixos"
"/var/lib/systemd/coredump"
"/etc/NetworkManager/system-connections"
{ directory = "/var/lib/colord"; user = "colord"; group = "colord"; mode = "u=rwx,g=rx,o="; }
];
files = [
"/etc/machine-id"
{ file = "/etc/nix/id_rsa"; parentDirectory = { mode = "u=rwx,g=,o="; }; }
];
};

hardware config

fileSystems."/mntroot" =
{ device = "/dev/disk/by-uuid/e68f113f-fd75-42d7-83f6-11162ee458ef";
fsType = "ext4";
neededForBoot = true;
};

fileSystems."/boot/efi" =
{ device = "/dev/disk/by-uuid/2F54-21C5";
fsType = "vfat";
options = [ "fmask=0022" "dmask=0022" ];
depends = [ "/boot" ];
};

fileSystems."/nix" =
{ device = "/dev/disk/by-uuid/ceded120-72ae-4d1d-a847-577eb072732c";
fsType = "ext4";
neededForBoot = true;
};

fileSystems."/boot" =
{ device = "/mntroot/boot";
fsType = "bind";
depends = [ "/mntroot" ];
};

fileSystems."/home" =
{ device = "/mntroot/home";
fsType = "bind";
depends = [ "/mntroot" ];
};

fileSystems."/" =
{ device = "none";
fsType = "tmpfs";
neededForBoot = true;
options = [ "size=200M" "mode=755" ]; # mode=755 so only root can write to those files
};