nixos/borgbackup: install job wrappers to systemPackages for easy borg access

Currently to run borg job manually, you have to use systemctl:
```
$ systemctl start borgbackup-job-jobname.service
```

This commit makes wrappers around borg jobs available in $PATH, which have
BORG_REPO and connection args set correctly:
```
$ borg-job-jobname list
$ borg-job-jobname mount ::jobname-archive-2019-12-25T00:01:29 /mnt/some-path
$ borg-job-jobname create ::test /some/path
```

Closes: https://github.com/NixOS/nixpkgs/pull/64888
Co-authored-by: Danylo Hlynskyi <abcz2.uprola@gmail.com>

1 files changed, 24 insertions, 3 deletions

diff --git a/nixos/modules/services/backup/borgbackup.nix b/nixos/modules/services/backup/borgbackup.nix
index 10d42325a6b1..a2eb80c55a8c 100644
--- a/nixos/modules/services/backup/borgbackup.nix
+++ b/nixos/modules/services/backup/borgbackup.nix
@@ -68,7 +68,7 @@ let
       { BORG_PASSPHRASE = passphrase; }
     else { };
 
-  mkBackupService = name: cfg: 
+  mkBackupService = name: cfg:
     let
       userHome = config.users.users.${cfg.user}.home;
     in nameValuePair "borgbackup-job-${name}" {
@@ -98,6 +98,23 @@ let
       inherit (cfg) startAt;
     };
 
+  # utility function around makeWrapper
+  mkWrapperDrv = {
+      original, name, set ? {}
+    }:
+    pkgs.runCommandNoCC "${name}-wrapper" {
+      buildInputs = [ pkgs.makeWrapper ];
+    } (with lib; ''
+      makeWrapper "${original}" "$out/bin/${name}" \
+        ${concatStringsSep " \\\n " (mapAttrsToList (name: value: ''--set ${name} "${value}"'') set)}
+    '');
+
+  mkBorgWrapper = name: cfg: mkWrapperDrv {
+    original = "${pkgs.borgbackup}/bin/borg";
+    name = "borg-job-${name}";
+    set = { BORG_REPO = cfg.repo; } // (mkPassEnv cfg) // cfg.environment;
+  };
+
   # Paths listed in ReadWritePaths must exist before service is started
   mkActivationScript = name: cfg:
     let
@@ -176,7 +193,11 @@ in {
   ###### interface
 
   options.services.borgbackup.jobs = mkOption {
-    description = "Deduplicating backups using BorgBackup.";
+    description = ''
+      Deduplicating backups using BorgBackup.
+      Adding a job will cause a borg-job-NAME wrapper to be added
+      to your system path, so that you can perform maintenance easily.
+    '';
     default = { };
     example = literalExample ''
       {
@@ -623,6 +644,6 @@ in {
 
       users = mkMerge (mapAttrsToList mkUsersConfig repos);
 
-      environment.systemPackages = with pkgs; [ borgbackup ];
+      environment.systemPackages = with pkgs; [ borgbackup ] ++ (mapAttrsToList mkBorgWrapper jobs);
     });
 }