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 1/2] 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;

From fd5664871fb33e2a9f8e0b023e568958aa959ad8 Mon Sep 17 00:00:00 2001
From: Simonas Kazlauskas <git@kazlauskas.me>
Date: Sat, 10 Feb 2024 22:25:24 +0200
Subject: [PATCH 2/2] review

---
 nixos/doc/manual/release-notes/rl-2405.section.md | 4 ++++
 nixos/lib/systemd-unit-options.nix                | 8 +-------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/nixos/doc/manual/release-notes/rl-2405.section.md b/nixos/doc/manual/release-notes/rl-2405.section.md
index 05c06ebcac1b..e11524f0de8a 100644
--- a/nixos/doc/manual/release-notes/rl-2405.section.md
+++ b/nixos/doc/manual/release-notes/rl-2405.section.md
@@ -286,6 +286,10 @@ The pre-existing [services.ankisyncd](#opt-services.ankisyncd.enable) has been m
   [fileSystems.overlay](#opt-fileSystems._name_.overlay.lowerdir). See also the
   [NixOS docs](#sec-overlayfs).
 
+- systemd units can now specify the `Upholds=` and `UpheldBy=` unit dependencies via the aptly
+  named `upholds` and `upheldBy` options. These options get systemd to enforce that the
+  dependencies remain continuosly running for as long as the dependent unit is in a running state.
+
 - `stdenv`: The `--replace` flag in `substitute`, `substituteInPlace`, `substituteAll`, `substituteAllStream`, and `substituteStream` is now deprecated if favor of the new `--replace-fail`, `--replace-warn` and `--replace-quiet`. The deprecated `--replace` equates to `--replace-warn`.
 
 - A new hardening flag, `zerocallusedregs` was made available, corresponding to the gcc/clang option `-fzero-call-used-regs=used-gpr`.
diff --git a/nixos/lib/systemd-unit-options.nix b/nixos/lib/systemd-unit-options.nix
index 9a0fedeb0b2d..df05d165d9e8 100644
--- a/nixos/lib/systemd-unit-options.nix
+++ b/nixos/lib/systemd-unit-options.nix
@@ -160,13 +160,7 @@ in rec {
         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.
+          Keeps the specified running while this unit is running. A continuous version of `wants`.
         '';
       };