From acf701b49a7687e23b4b18701d4ab62285dec029 Mon Sep 17 00:00:00 2001
From: cy <hi@cything.io>
Date: Mon, 30 Dec 2024 14:29:06 -0500
Subject: [PATCH] nixos/btrbk: add snapshotOnly option

---
 doc/manpage-urls.json                   |  1 +
 nixos/modules/services/backup/btrbk.nix | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/doc/manpage-urls.json b/doc/manpage-urls.json
index d6e9d163c1128..63f877dcb6604 100644
--- a/doc/manpage-urls.json
+++ b/doc/manpage-urls.json
@@ -3,6 +3,7 @@
   "binfmt.d(5)": "https://www.freedesktop.org/software/systemd/man/binfmt.d.html",
   "bootctl(1)": "https://www.freedesktop.org/software/systemd/man/bootctl.html",
   "bootup(7)": "https://www.freedesktop.org/software/systemd/man/bootup.html",
+  "btrbk(1)": "https://digint.ch/btrbk/doc/btrbk.1.html",
   "busctl(1)": "https://www.freedesktop.org/software/systemd/man/busctl.html",
   "cat(1)": "https://www.gnu.org/software/coreutils/manual/html_node/cat-invocation.html",
   "coredump.conf(5)": "https://www.freedesktop.org/software/systemd/man/coredump.conf.html",
diff --git a/nixos/modules/services/backup/btrbk.nix b/nixos/modules/services/backup/btrbk.nix
index a3745e3e6f716..03cf7d08fa5ae 100644
--- a/nixos/modules/services/backup/btrbk.nix
+++ b/nixos/modules/services/backup/btrbk.nix
@@ -185,6 +185,17 @@ in
                   Setting it to null disables the timer, thus this instance can only be started manually.
                 '';
               };
+              snapshotOnly = mkOption {
+                type = types.bool;
+                default = false;
+                description = ''
+                  Whether to run in snapshot only mode. This skips backup creation and deletion steps.
+                  Useful when you want to manually backup to an external drive that might not always be connected.
+                  Use `btrbk -c /path/to/conf resume` to trigger manual backups.
+                  More examples [here](https://github.com/digint/btrbk#example-backups-to-usb-disk).
+                  See also `snapshot` subcommand in {manpage}`btrbk(1)`.
+                '';
+              };
               settings = mkOption {
                 type = types.submodule {
                   freeformType =
@@ -353,7 +364,9 @@ in
           User = "btrbk";
           Group = "btrbk";
           Type = "oneshot";
-          ExecStart = "${pkgs.btrbk}/bin/btrbk -c /etc/btrbk/${name}.conf run";
+          ExecStart = "${pkgs.btrbk}/bin/btrbk -c /etc/btrbk/${name}.conf ${
+            if instance.snapshotOnly then "snapshot" else "run"
+          }";
           Nice = cfg.niceness;
           IOSchedulingClass = cfg.ioSchedulingClass;
           StateDirectory = "btrbk";