lxcfs: add module

nixos/modules/module-list.nix

@@ -618,6 +618,7 @@
   ./virtualisation/docker.nix
   ./virtualisation/libvirtd.nix
   ./virtualisation/lxc.nix
+  ./virtualisation/lxcfs.nix
   ./virtualisation/lxd.nix
   ./virtualisation/amazon-options.nix
   ./virtualisation/openvswitch.nix

nixos/modules/virtualisation/lxcfs.nix

@@ -0,0 +1,49 @@
+# LXC Configuration
+
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.virtualisation.lxc.lxcfs;
+in {
+  meta.maintainers = [ maintainers.mic92 ];
+
+  ###### interface
+  options.virtualisation.lxc.lxcfs = {
+    enable =
+      mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          This enables LXCFS, a FUSE filesystem for LXC.
+          To use lxcfs in include the following configuration in your
+          container configuration:
+          <code>
+            virtualisation.lxc.defaultConfig = "lxc.include = ''${pkgs.lxcfs}/share/lxc/config/common.conf.d/00-lxcfs.conf";
+          </code>
+        '';
+      };
+  };
+
+  ###### implementation
+  config = mkIf cfg.enable {
+    services.cgmanager.enable = true;
+
+    systemd.services.lxcfs = {
+      description = "FUSE filesystem for LXC";
+      wantedBy = [ "multi-user.target" ];
+      requires = [ "cgmanager.service" ];
+      after = [ "cgmanager.service" ];
+      before = [ "lxc.service" ];
+      restartIfChanged = false;
+      serviceConfig = {
+        ExecStartPre="${pkgs.coreutils}/bin/mkdir -p /var/lib/lxcfs";
+        ExecStart="${pkgs.lxcfs}/bin/lxcfs /var/lib/lxcfs";
+        ExecStopPost="-${pkgs.fuse}/bin/fusermount -u /var/lib/lxcfs";
+        KillMode="process";
+        Restart="on-failure";
+      };
+    };
+  };
+}