nixos/lxd: add preseed option

nixos/modules/virtualisation/lxd.nix

@@ -4,6 +4,7 @@
 
 let
   cfg = config.virtualisation.lxd;
+  preseedFormat = pkgs.formats.yaml {};
 in {
   imports = [
     (lib.mkRemovedOptionModule [ "virtualisation" "lxd" "zfsPackage" ] "Override zfs in an overlay instead to override it globally")
@@ -73,6 +74,65 @@ in {
         '';
       };
 
+      preseed = lib.mkOption {
+        type = lib.types.nullOr (lib.types.submodule {
+          freeformType = preseedFormat.type;
+        });
+
+        default = null;
+
+        description = lib.mdDoc ''
+          Configuration for LXD preseed, see
+          <https://documentation.ubuntu.com/lxd/en/latest/howto/initialize/#initialize-preseed>
+          for supported values.
+
+          Changes to this will be re-applied to LXD which will overwrite existing entities or create missing ones,
+          but entities will *not* be removed by preseed.
+        '';
+
+        example = lib.literalExpression ''
+          {
+            networks = [
+              {
+                name = "lxdbr0";
+                type = "bridge";
+                config = {
+                  "ipv4.address" = "10.0.100.1/24";
+                  "ipv4.nat" = "true";
+                };
+              }
+            ];
+            profiles = [
+              {
+                name = "default";
+                devices = {
+                  eth0 = {
+                    name = "eth0";
+                    network = "lxdbr0";
+                    type = "nic";
+                  };
+                  root = {
+                    path = "/";
+                    pool = "default";
+                    size = "35GiB";
+                    type = "disk";
+                  };
+                };
+              }
+            ];
+            storage_pools = [
+              {
+                name = "default";
+                driver = "dir";
+                config = {
+                  source = "/var/lib/lxd/storage-pools/default";
+                };
+              }
+            ];
+          }
+        '';
+      };
+
       startTimeout = lib.mkOption {
         type = lib.types.int;
         default = 600;
@@ -176,6 +236,21 @@ in {
       };
     };
 
+    systemd.services.lxd-preseed = lib.mkIf (cfg.preseed != null) {
+      description = "LXD initialization with preseed file";
+      wantedBy = ["multi-user.target"];
+      requires = ["lxd.service"];
+      after = ["lxd.service"];
+
+      script = ''
+        ${pkgs.coreutils}/bin/cat ${preseedFormat.generate "lxd-preseed.yaml" cfg.preseed} | ${cfg.package}/bin/lxd init --preseed
+      '';
+
+      serviceConfig = {
+        Type = "oneshot";
+      };
+    };
+
     users.groups.lxd = {};
 
     users.users.root = {

nixos/tests/lxd/container.nix

@@ -49,6 +49,9 @@ in {
     # Wait for lxd to settle
     machine.succeed("lxd waitready")
 
+    # no preseed should mean no service
+    machine.fail("systemctl status lxd-preseed.service")
+
     machine.succeed("lxd init --minimal")
 
     machine.succeed(

nixos/tests/lxd/default.nix

@@ -5,6 +5,7 @@
 }: {
   container = import ./container.nix {inherit system pkgs;};
   nftables = import ./nftables.nix {inherit system pkgs;};
+  preseed = import ./preseed.nix {inherit system pkgs;};
   ui = import ./ui.nix {inherit system pkgs;};
   virtual-machine = import ./virtual-machine.nix { inherit system pkgs; };
 }

nixos/tests/lxd/preseed.nix

@@ -0,0 +1,71 @@
+import ../make-test-python.nix ({ pkgs, lib, ... } :
+
+{
+  name = "lxd-preseed";
+
+  meta = {
+    maintainers = with lib.maintainers; [ adamcstephens ];
+  };
+
+  nodes.machine = { lib, ... }: {
+    virtualisation = {
+      diskSize = 4096;
+
+      lxc.lxcfs.enable = true;
+      lxd.enable = true;
+
+      lxd.preseed = {
+        networks = [
+          {
+            name = "nixostestbr0";
+            type = "bridge";
+            config = {
+              "ipv4.address" = "10.0.100.1/24";
+              "ipv4.nat" = "true";
+            };
+          }
+        ];
+        profiles = [
+          {
+            name = "nixostest_default";
+            devices = {
+              eth0 = {
+                name = "eth0";
+                network = "nixostestbr0";
+                type = "nic";
+              };
+              root = {
+                path = "/";
+                pool = "default";
+                size = "35GiB";
+                type = "disk";
+              };
+            };
+          }
+        ];
+        storage_pools = [
+          {
+            name = "nixostest_pool";
+            driver = "dir";
+          }
+        ];
+      };
+    };
+  };
+
+  testScript = ''
+    def wait_for_preseed(_) -> bool:
+      _, output = machine.systemctl("is-active lxd-preseed.service")
+      return ("inactive" in output)
+
+    machine.wait_for_unit("sockets.target")
+    machine.wait_for_unit("lxd.service")
+    with machine.nested("Waiting for preseed to complete"):
+      retry(wait_for_preseed)
+
+    with subtest("Verify preseed resources created"):
+      machine.succeed("lxc profile show nixostest_default")
+      machine.succeed("lxc network info nixostestbr0")
+      machine.succeed("lxc storage show nixostest_pool")
+  '';
+})