add btrfs subvolumes

default.nix

@@ -69,6 +69,18 @@ let
 
   create-f = q: x: create.${x.type} q x;
 
+  create.btrfs = q: x: ''
+    mkfs.btrfs ${q.device}
+    ${lib.optionalString (!isNull x.subvolumes or null) ''
+      MNTPOINT=$(mktemp -d)
+      (
+        mount ${q.device} "$MNTPOINT"
+        trap 'umount $MNTPOINT; rm -rf $MNTPOINT' EXIT
+        ${concatMapStringsSep "\n" (subvolume: "btrfs subvolume create \"$MNTPOINT\"/${subvolume}") x.subvolumes}
+      )
+    ''}
+  '';
+
   create.filesystem = q: x: ''
     mkfs.${x.format} ${q.device}
   '';
@@ -178,6 +190,8 @@ let
       '';
     };
 
+  mount.btrfs = mount.filesystem;
+
   mount.devices = q: x: let
     z = foldl' recursiveUpdate {} (mapAttrsToList (name: mount-f { device = "/dev/${name}"; inherit name; }) x.content);
     # attrValues returns values sorted by name.  This is important, because it

example/btrfs-subvolumes.nix

@@ -0,0 +1,26 @@
+{
+  type = "devices";
+  content = {
+    vdb = {
+      type = "table";
+      format = "gpt";
+      partitions = [
+        {
+          type = "partition";
+          part-type = "primary";
+          start = "0%";
+          end = "100%";
+          content = {
+            type = "btrfs";
+            mountpoint = "/";
+            subvolumes = [
+              "/home"
+              "/test"
+            ];
+          };
+        }
+      ];
+    };
+  };
+}
+

tests/btrfs-subvolumes.nix

@@ -0,0 +1,40 @@
+{ makeTest ? import <nixpkgs/nixos/tests/make-test-python.nix>
+, pkgs ? (import <nixpkgs> {})
+}:
+let
+  makeTest' = args:
+    makeTest args {
+      inherit pkgs;
+      inherit (pkgs) system;
+    };
+  disko-config = import ../example/btrfs-subvolumes.nix;
+  tsp-create = pkgs.writeScript "create" ((pkgs.callPackage ../. {}).create disko-config);
+  tsp-mount = pkgs.writeScript "mount" ((pkgs.callPackage ../. {}).mount disko-config);
+in makeTest' {
+  name = "disko";
+
+  nodes.machine =
+    { config, pkgs, modulesPath, ... }:
+
+    {
+      imports = [
+        (modulesPath + "/profiles/installation-device.nix")
+        (modulesPath + "/profiles/base.nix")
+      ];
+
+      # speed-up eval
+      documentation.enable = false;
+
+      virtualisation.emptyDiskImages = [ 512 ];
+    };
+
+  testScript = ''
+    machine.succeed("echo 'secret' > /tmp/secret.key");
+    machine.succeed("${tsp-create}");
+    machine.succeed("${tsp-mount}");
+    machine.succeed("${tsp-mount}"); # verify that the command is idempotent
+    machine.succeed("test -e /mnt/test");
+    machine.succeed("btrfs subvolume list /mnt | grep -qs 'path test$'");
+  '';
+}
+