From ae67327df3faaf106d2bcb352d4151774576bf00 Mon Sep 17 00:00:00 2001
From: Gregor Kleen <gkleen@yggdrasil.li>
Date: Fri, 29 Dec 2023 22:40:38 +0100
Subject: ...

---
 hosts/surtr/postgresql/default.nix  |  8 +++++++-
 hosts/vidhar/pgbackrest/default.nix |  8 +++++++-
 modules/pgbackrest.nix              | 41 ++++++++++++++++++++++++++++---------
 3 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/hosts/surtr/postgresql/default.nix b/hosts/surtr/postgresql/default.nix
index faf74588..f0e42ee8 100644
--- a/hosts/surtr/postgresql/default.nix
+++ b/hosts/surtr/postgresql/default.nix
@@ -1,6 +1,11 @@
 { pkgs, sources, config, flake, flakeInputs, ... }:
 let
   versioning = sources.psql-versioning.src;
+
+  nixpkgs-pgbackrest = import (flakeInputs.nixpkgs-pgbackrest.outPath + "/pkgs/top-level") {
+    overlays = [ flake.overlays.libdscp ];
+    localSystem = config.nixpkgs.system;
+  };
 in {
   config = {
     assertions = [
@@ -16,7 +21,8 @@ in {
 
     services.pgbackrest = {
       enable = true;
-      package = flakeInputs.nixpkgs-pgbackrest.legacyPackages.${config.nixpkgs.system}.pgbackrest;
+      package = nixpkgs-pgbackrest.pgbackrest;
+      dscpPackage = nixpkgs-pgbackrest.libdscp;
 
       settings = {
         "surtr" = {
diff --git a/hosts/vidhar/pgbackrest/default.nix b/hosts/vidhar/pgbackrest/default.nix
index fec0c1fb..ffb149f5 100644
--- a/hosts/vidhar/pgbackrest/default.nix
+++ b/hosts/vidhar/pgbackrest/default.nix
@@ -2,6 +2,11 @@
 
 let
   surtrRepoCfg = flake.nixosConfigurations."surtr".config.services.pgbackrest.settings.surtr;
+
+  nixpkgs-pgbackrest = import (flakeInputs.nixpkgs-pgbackrest.outPath + "/pkgs/top-level") {
+    overlays = [ flake.overlays.libdscp ];
+    localSystem = config.nixpkgs.system;
+  };
 in {
   config = {
     assertions = [
@@ -12,7 +17,8 @@ in {
 
     services.pgbackrest = {
       enable = true;
-      package = flakeInputs.nixpkgs-pgbackrest.legacyPackages.${config.nixpkgs.system}.pgbackrest;
+      package = nixpkgs-pgbackrest.pgbackrest;
+      dscpPackage = nixpkgs-pgbackrest.libdscp;
 
       tlsServer = {
         enable = true;
diff --git a/modules/pgbackrest.nix b/modules/pgbackrest.nix
index cc865bca..e02849f5 100644
--- a/modules/pgbackrest.nix
+++ b/modules/pgbackrest.nix
@@ -36,6 +36,10 @@ let
     } "=";
   };
 
+  mkDSCPOption = options: mkOption {
+    type = types.numbers.between 0 63;
+  } // options;
+
   loglevelType = types.enum ["off" "error" "warn" "info" "detail" "debug" "trace"];
   inherit (utils.systemdUtils.unitOptions) unitOption;
 in {
@@ -44,6 +48,10 @@ in {
       enable = mkEnableOption "pgBackRest";
 
       package = mkPackageOption pkgs "pgbackrest" {};
+      dscpPackage = mkPackageOption pkgs "libdscp" { nullable = true; default = null; };
+
+      dscp.archive-push = mkDSCPOption { default = 24; };
+      dscp.backup = mkDSCPOption { default = 8; };
 
       configurePostgresql = {
         enable = mkEnableOption "configuring PostgreSQL for sending WAL to pgBackRest" // {
@@ -145,14 +153,32 @@ in {
     environment.systemPackages = [ cfg.package ];
 
     services.postgresql.settings = mkIf cfg.configurePostgresql.enable {
-      archive_command = "pgbackrest --stanza ${escapeSystemdExecArg cfg.configurePostgresql.stanza} archive-push %p";
+      archive_command = let
+        pgbackrest-dscp-wrapped = pkgs.writeShellApplication {
+          name = "pgbackrest-dscp";
+          runtimeInputs = [ cfg.package ];
+          text = ''
+            export LD_PRELOAD
+            LD_PRELOAD=''${LD_PRELOAD:+':'$LD_PRELOAD':'}
+            if [[ $LD_PRELOAD != *':'''${cfg.dscpPackage}/lib/libdscp.so''':'* ]]; then
+                LD_PRELOAD='${cfg.dscpPackage}/lib/libdscp.so'$LD_PRELOAD
+            fi
+            LD_PRELOAD=''${LD_PRELOAD#':'}
+            LD_PRELOAD=''${LD_PRELOAD%':'}
+
+            : "''${DSCP:=${toString cfg.dscp.archive-push}}"
+
+            exec -- pgbackrest "$@"
+          '';
+        };
+        pgbackrest = if cfg.dscpPackage != null then "${pgbackrest-dscp-wrapped}/bin/pgbackrest-dscp" else "${cfg.package}/bin/pgbackrest";
+      in "${pgbackrest} --stanza ${escapeShellArg cfg.configurePostgresql.stanza} archive-push %p";
       archive_mode = true;
       max_wal_senders = mkDefault 3;
       wal_level = "replica";
     };
 
     systemd.services = {
-      postgresql.path = mkIf cfg.configurePostgresql.enable [ cfg.package ];
       pgbackrest-tls-server = mkIf cfg.tlsServer.enable {
         description = "pgBackRest TLS-Server";
         wantedBy = [ "multi-user.target" ];
@@ -172,11 +198,6 @@ in {
           Group = cfg.tlsServer.group;
           ExecStart = "${cfg.package}/bin/pgbackrest server";
           ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
-
-          Environment = [
-            "LD_PRELOAD=${pkgs.libdscp}/lib/libdscp.so"
-            "DSCP=8"
-          ];
         };
       };
     } // mapAttrs' (name: backupCfg: nameValuePair "pgbackrest-backup@${escapeSystemdPath name}" {
@@ -189,9 +210,9 @@ in {
         Restart = "on-failure";
         RestartSec = "5min";
 
-        Environment = [
-          "LD_PRELOAD=${pkgs.libdscp}/lib/libdscp.so"
-          "DSCP=8"
+        Environment = mkIf (cfg.dscpPackage != null) [
+          "LD_PRELOAD=\"${cfg.dscpPackage}/lib/libdscp.so\""
+          "DSCP=\"${toString cfg.dscp.backup}\""
         ];
       };
     }) cfg.backups;
-- 
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