nixos/borgbackup: let borg write to disk and see /tmp, add extraArgs

nixos/modules/services/backup/borgbackup.nix

@@ -35,25 +35,26 @@ let
     ${cfg.preHook}
   '' + optionalString cfg.doInit ''
     # Run borg init if the repo doesn't exist yet
-    if ! borg list > /dev/null; then
-      borg init \
+    if ! borg list ${cfg.extraArgs} > /dev/null; then
+      borg init ${cfg.extraArgs} \
         --encryption ${cfg.encryption.mode} \
         $extraInitArgs
       ${cfg.postInit}
     fi
   '' + ''
-    borg create \
+    borg create ${cfg.extraArgs} \
       --compression ${cfg.compression} \
       --exclude-from ${mkExcludeFile cfg} \
       $extraCreateArgs \
       "::$archiveName$archiveSuffix" \
       ${escapeShellArgs cfg.paths}
   '' + optionalString cfg.appendFailedSuffix ''
-    borg rename "::$archiveName$archiveSuffix" "$archiveName"
+    borg rename ${cfg.extraArgs} \
+      "::$archiveName$archiveSuffix" "$archiveName"
   '' + ''
     ${cfg.postCreate}
   '' + optionalString (cfg.prune.keep != { }) ''
-    borg prune \
+    borg prune ${cfg.extraArgs} \
       ${mkKeepArgs cfg} \
       --prefix ${escapeShellArg cfg.prune.prefix} \
       $extraPruneArgs
@@ -85,9 +86,10 @@ let
         ProtectSystem = "strict";
         ReadWritePaths =
           [ "${userHome}/.config/borg" "${userHome}/.cache/borg" ]
+          ++ cfg.readWritePaths
           # Borg needs write access to repo if it is not remote
           ++ optional (isLocalPath cfg.repo) cfg.repo;
-        PrivateTmp = true;
+        PrivateTmp = cfg.privateTmp;
       };
       environment = {
         BORG_REPO = cfg.repo;
@@ -318,6 +320,30 @@ in {
             ];
           };
 
+          readWritePaths = mkOption {
+            type = with types; listOf path;
+            description = ''
+              By default, borg cannot write anywhere on the system but
+              <literal>$HOME/.config/borg</literal> and <literal>$HOME/.cache/borg</literal>.
+              If, for example, your preHook script needs to dump files
+              somewhere, put those directories here.
+            '';
+            default = [ ];
+            example = [
+              "/var/backup/mysqldump"
+            ];
+          };
+
+          privateTmp = mkOption {
+            type = types.bool;
+            description = ''
+              Set the <literal>PrivateTmp</literal> option for
+              the systemd-service. Set to false if you need sockets
+              or other files from global /tmp.
+            '';
+            default = true;
+          };
+
           doInit = mkOption {
             type = types.bool;
             description = ''
@@ -430,6 +456,16 @@ in {
             default = "";
           };
 
+          extraArgs = mkOption {
+            type = types.str;
+            description = ''
+              Additional arguments for all <command>borg</command> calls the
+              service has. Handle with care.
+            '';
+            default = "";
+            example = "--remote-path=borg1";
+          };
+
           extraInitArgs = mkOption {
             type = types.str;
             description = ''