nixos-hardware/microsoft/hyper-v

This is a setup for installing NixOS in Hyper-V as a guest.

I don't have details handy anymore on the detailed steps I had to do on the Windows host (there's no NixWindows yet, unfortunately...), so you'll have to try googling that yourself, e.g. something like "linux on hyper-v" or "ubuntu on hyper-v". (You're welcome to send PRs with improvements of this guide.) Below, I'm providing only the info with what to do on the NixOS side of things.

Installation

I basically followed the guide for NixOS on VirtualBox. However, some additional changes in /etc/nixos/configuration.nix were required to really make it work (I don't include them as a .nix file, as they must be done before nixos-install, and I'm not sure how to proceed with cloning the nixos-hardware repo at this stage):

# REQUIRED - see: https://github.com/nixos/nixpkgs/issues/9899
boot.initrd.kernelModules = ["hv_vmbus" "hv_storvsc"];

# RECOMMENDED
# - use 800x600 resolution for text console, to make it easy to fit on screen
boot.kernelParams = ["video=hyperv_fb:800x600"];  # https://askubuntu.com/a/399960
# - avoid a problem with `nix-env -i` running out of memory
boot.kernel.sysctl."vm.overcommit_memory" = "1"; # https://github.com/NixOS/nix/issues/421

# UNKNOWN - not sure if below are needed; were suggested for VirtualBox and I used them
boot.loader.grub.device = "/dev/sda";
boot.initrd.checkJournalingFS = false;

Shared folder

To share a folder between Windows host and Linux/NixOS guest, the typical solution seems to be to make a folder "shared" on Windows, then access it via Samba from NixOS. On the Windows host, I had to make an additional virtual switch in Hyper-V Manager, with mode "internal". Then in properties of the virtual network card on Windows host (attached to the virtual switch), I changed the IP to a fixed 10.0.0.100 (mask 255.255.255.240). I also added a special purpose user on the host, with some long randomly generated password, to act as Samba credentials for NixOS. To test that it works, I used the following commands:

$ nix-env -iA nixos.samba
$ smbclient -L //10.0.0.100 -U shares-guest%ReplaceWithSomeLongRandomlyGeneratedPassword
Domain=[DESKTOP-ABCD123] OS=[Windows 10 Pro 14393] Server=[Windows 10 Pro 6.3]

	Sharename       Type      Comment
	---------       ----      -------
	ADMIN$          Disk      Administracja zdalna
	C$              Disk      Domyślny udział
	IPC$            IPC       Zdalne wywołanie IPC 
	shared-space    Disk      
Connection to 10.0.0.100 failed (Error NT_STATUS_RESOURCE_NAME_NOT_FOUND)
NetBIOS over TCP disabled -- no workgroup available

$ nix-env -e samba

Then I added the following lines in /etc/nixos/configuration.nix:

# Client for shared folder on Windows Hyper-V host
# Based on: nixpkgs.git/nixos/tests/samba.nix
fileSystems."/vm-share" = {
  fsType = "cifs";
  device = "//10.0.0.100/shared-space";
  options = [ "username=shares-guest" "password=ReplaceWithSomeLongRandomlyGeneratedPassword" ];
};
networking.interfaces.eth1.ip4 = [{address="10.0.0.101"; prefixLength=28;}];