pkgs.uvms: init

...with some basic optional persistence and without having to rebuild
images for every app

nix run -f . pkgs.uvms -- --persist-home librewolf alacritty --run librewolf --run alacritty

pkgs/mkSystemdDropin.nix

@@ -0,0 +1,39 @@
+{
+  lib,
+  runCommand,
+  writeShellScriptBin,
+}:
+{
+  name,
+  prefix ? "10-all-",
+  dirs ? [
+    "service"
+    "mount"
+    "socket"
+    "timer"
+    "target"
+  ],
+
+  dropinText ? null,
+  extraCommands ? "",
+  ...
+}@args:
+
+runCommand "${name}-dropin"
+  (
+    lib.removeAttrs args [
+      "name"
+    ]
+    // {
+      inherit dirs dropinText extraCommands;
+    }
+  )
+  ''
+    set -euo pipefail
+    root=$out/lib/systemd/system
+    for dir in $dirs ; do
+      mkdir -p "$root/$dir".d
+      printf "%s" "$dropinText" > "$root/$dir.d/${prefix}${name}.conf"
+    done
+    runHook extraCommands
+  ''