add btrfs root

machines/laptop/hardware-configuration.nix

@@ -18,11 +18,38 @@
   boot.extraModulePackages = [];
 
   fileSystems."/" = {
-    device = "none";
+    #device = "none";
-    fsType = "tmpfs";
+    #fsType = "tmpfs";
-    options = ["defaults" "size=60%" "mode=755"];
+    #options = ["defaults" "size=60%" "mode=755"];
+    device = "/dev/disk/by-uuid/16c93673-4f0e-4010-a7f4-7ccffb20edb7";
+    fsType = "btrfs";
   };
 
+  boot.initrd.postResumeCommands = lib.mkAfter ''
+    mkdir /btrfs_tmp
+    mount ${config.fileSystems."/".device} /btrfs_tmp
+    if [[ -e /btrfs_tmp/root ]]; then
+      mkdir -p /btrfs_tmp/old_roots
+      timestamp=$(date --date="@$(stat -c %Y /btrfs_tmp/root)" "+%Y-%m-%-d_%H:$M:%S")
+      mv /btrfs_tmp/root "/btrfs_tmp/old_roots/$timestamp"
+    fi
+
+    delete_subvolume_recursively() {
+      IFS=$'\n'
+      for i in $(btrfs subvolume list -o "$1" | cut -f 9- -d ' '); do
+        delete_subvolume_recursively "/btrfs_tmp/$i"
+      done
+      btrfs subvolume delete "$1"
+    }
+
+    for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
+      delete_subvolume_recursively "$i"
+    done
+
+    btrfs subvolume create /btrfs_tmp/root
+    umount /btrfs_tmp
+  '';
+
   fileSystems."/nix" = {
     device = "/dev/disk/by-uuid/0e586651-36f4-42b0-99b3-3f0704a894d6";
     fsType = "btrfs";