delet old btrfs root

devices/ellaca/hardware-config.nix

@@ -1,8 +1,36 @@
 { config, lib, ... }: {
-  boot.initrd.availableKernelModules = [ "nvme" "xhci_pci" "ahci" "usb_storage" "usbhid" "sd_mod" ];
-  boot.initrd.kernelModules = [ ];
-  boot.kernelModules = [ "kvm-amd" ];
-  boot.extraModulePackages = [ ];
+  boot = {
+    initrd = {
+      availableKernelModules = [ "nvme" "xhci_pci" "ahci" "usb_storage" "usbhid" "sd_mod" ];
+      kernelModules = [ ];
+      postDeviceCommands = lib.mkAfter ''
+        mkdir /btrfs_tmp
+        mount /dev/disk/by-uuid/b6e6bca7-1435-4b41-b174-8550eace7c32 /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
+      '';
+    };
+    kernelModules = [ "kvm-amd" ];
+    extraModulePackages = [ ];
+  };
 
   fileSystems = {
     "/boot" = {

outputs.nix

@@ -39,7 +39,7 @@
       };
       modules = [
         ./devices/ellaca
-        ] ++ clientModules;
+      ] ++ clientModules;
     };
 
     # Surface Pro 7 (i5 128GB)