From 74eeb75af1ea94c2f639a843172ee2fc82f5cf54 Mon Sep 17 00:00:00 2001
From: Simonas Kazlauskas <git@kazlauskas.me>
Date: Sat, 10 Feb 2024 13:43:31 +0200
Subject: [PATCH] systemd: add support for upholds and upheldBy

---
 nixos/lib/systemd-lib.nix          | 10 +++++++++-
 nixos/lib/systemd-unit-options.nix | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/nixos/lib/systemd-lib.nix b/nixos/lib/systemd-lib.nix
index 347ee7303936..c9cca619ed70 100644
--- a/nixos/lib/systemd-lib.nix
+++ b/nixos/lib/systemd-lib.nix
@@ -242,7 +242,7 @@ in rec {
             ln -sfn '${name}' $out/'${name2}'
           '') (unit.aliases or [])) units)}
 
-      # Create .wants and .requires symlinks from the wantedBy and
+      # Create .wants, .upholds and .requires symlinks from the wantedBy, upheldBy and
       # requiredBy options.
       ${concatStrings (mapAttrsToList (name: unit:
           concatMapStrings (name2: ''
@@ -250,6 +250,12 @@ in rec {
             ln -sfn '../${name}' $out/'${name2}.wants'/
           '') (unit.wantedBy or [])) units)}
 
+      ${concatStrings (mapAttrsToList (name: unit:
+          concatMapStrings (name2: ''
+            mkdir -p $out/'${name2}.upholds'
+            ln -sfn '../${name}' $out/'${name2}.upholds'/
+          '') (unit.upheldBy or [])) units)}
+
       ${concatStrings (mapAttrsToList (name: unit:
           concatMapStrings (name2: ''
             mkdir -p $out/'${name2}.requires'
@@ -289,6 +295,8 @@ in rec {
           { Requires = toString config.requires; }
         // optionalAttrs (config.wants != [])
           { Wants = toString config.wants; }
+        // optionalAttrs (config.upholds != [])
+          { Upholds = toString config.upholds; }
         // optionalAttrs (config.after != [])
           { After = toString config.after; }
         // optionalAttrs (config.before != [])
diff --git a/nixos/lib/systemd-unit-options.nix b/nixos/lib/systemd-unit-options.nix
index 9c69bda471bb..9a0fedeb0b2d 100644
--- a/nixos/lib/systemd-unit-options.nix
+++ b/nixos/lib/systemd-unit-options.nix
@@ -74,6 +74,15 @@ in rec {
       '';
     };
 
+    upheldBy = mkOption {
+      default = [];
+      type = types.listOf unitNameType;
+      description = lib.mdDoc ''
+        Keep this unit running as long as the listed units are running. This is a continuously
+        enforced version of wantedBy.
+      '';
+    };
+
     wantedBy = mkOption {
       default = [];
       type = types.listOf unitNameType;
@@ -147,6 +156,20 @@ in rec {
         '';
       };
 
+      upholds = mkOption {
+        default = [];
+        type = types.listOf unitNameType;
+        description = lib.mdDoc ''
+          Configures dependencies similar to Wants=, but as long as this unit is up, all units
+          listed in Upholds= are started whenever found to be inactive or failed, and no job is
+          queued for them. While a Wants= dependency on another unit has a one-time effect when
+          this units started, a Upholds= dependency on it has a continuous effect, constantly
+          restarting the unit if necessary. This is an alternative to the Restart= setting of
+          service units, to ensure they are kept running whatever happens. The restart happens
+          without delay, and usual per-unit rate-limit applies.
+        '';
+      };
+
       after = mkOption {
         default = [];
         type = types.listOf unitNameType;