WIP: kopia backup script

common/global/backup.nix

@@ -1,6 +1,6 @@
 { pkgs, ... }:
 {
-  environment.systemPackages = [ pkgs.kopia ];
+  environment.systemPackages = [ pkgs.unstable.kopia ];
 
   #  systemd = {
   #    services = {

common/global/kopia-snapshot-backup.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+set -Eeuxo pipefail
+
+target_path="/persist"
+snapshot_path="$target_path/kopia-backup-snapshot"
+
+if [ -e "$snapshot_path" ] && btrfs subvolume delete "$snapshot_path"; then
+    echo "Deleted leftover old snapshot."
+fi
+
+btrfs subvolume snapshot -r "$target_path" "$snapshot_path"
+
+# --no-send-snapshot-path due to https://github.com/kopia/kopia/issues/4402
+kopia snapshot create --no-send-snapshot-report --override-source "$target_path" "$@" -- "$snapshot_path"
+
+btrfs subvolume delete "$snapshot_path"