nixos/postgresql: support 0750 for data directory (#65245)

* nixos/postgresql: support 0750 for data directory

This is rework of part of https://github.com/NixOS/nixpkgs/pull/46670.
My usecase was to be able to inspect PG datadir as wheel user.

PG11 now allows starting server with 0750 mask for data dir.
`groupAccess = true` now does this automatically. The only thing you have to do
is to set group ownership.

For PG10 and below, I've described a hack how this can be done. Before this PR
hack was impossible. The hack isn't ideal, because there is short
period of time when dir mode is 0700, so I didn't want to make it official.

Test/example is present too.

* postgresql: allow changing initidb arguments via module system

Closes https://github.com/NixOS/nixpkgs/issues/18829

+ some cleanups

* addressed review comments and some fixes

* whoops

* change groupAccess to tristate, to not force `chmod` on dataDir.

Making mask either 0700 or 0750 is too restrictive..

* WIP

* let's not support group mode for versions pre-11.

The only fix is to change mode to 0700 before start, because otherwise postgresql
doesn't start, and error is non-obvious.

nixos/modules/services/databases/postgresql.nix

@@ -22,6 +22,8 @@ let
       ${cfg.extraConfig}
     ''; 
 
+  groupAccessAvailable = versionAtLeast postgresql.version "11.0";
+
 in
 
 {
@@ -88,6 +90,16 @@ in
         '';
       };
 
+      initdbArgs = mkOption {
+        type = with types; listOf str;
+        default = [];
+        example = [ "--data-checksums" "--allow-group-access" ];
+        description = ''
+          Additional arguments passed to <literal>initdb<literal> during data dir
+          initialisation.
+        '';
+      };
+
       initialScript = mkOption {
         type = types.nullOr types.path;
         default = null;
@@ -220,7 +232,7 @@ in
 
   ###### implementation
 
-  config = mkIf config.services.postgresql.enable {
+  config = mkIf cfg.enable {
 
     services.postgresql.package =
       # Note: when changing the default, make it conditional on
@@ -232,8 +244,9 @@ in
             else throw "postgresql_9_4 was removed, please upgrade your postgresql version.");
 
     services.postgresql.dataDir =
-      mkDefault (if versionAtLeast config.system.stateVersion "17.09" then "/var/lib/postgresql/${config.services.postgresql.package.psqlSchema}"
+      mkDefault (if versionAtLeast config.system.stateVersion "17.09"
-                 else "/var/db/postgresql");
+                  then "/var/lib/postgresql/${cfg.package.psqlSchema}"
+                  else "/var/db/postgresql");
 
     services.postgresql.authentication = mkAfter
       ''
@@ -284,7 +297,7 @@ in
           ''
             # Initialise the database.
             if ! test -e ${cfg.dataDir}/PG_VERSION; then
-              initdb -U ${cfg.superUser}
+              initdb -U ${cfg.superUser} ${concatStringsSep " " cfg.initdbArgs}
               # See postStart!
               touch "${cfg.dataDir}/.first_startup"
             fi
@@ -293,8 +306,12 @@ in
               ln -sfn "${pkgs.writeText "recovery.conf" cfg.recoveryConfig}" \
                 "${cfg.dataDir}/recovery.conf"
             ''}
+            ${optionalString (!groupAccessAvailable) ''
+              # postgresql pre 11.0 doesn't start if state directory mode is group accessible
+              chmod 0700 "${cfg.dataDir}"
+            ''}
 
-             exec postgres
+            exec postgres
           '';
 
         serviceConfig =
@@ -303,7 +320,7 @@ in
             Group = "postgres";
             PermissionsStartOnly = true;
             RuntimeDirectory = "postgresql";
-            Type = if lib.versionAtLeast cfg.package.version "9.6"
+            Type = if versionAtLeast cfg.package.version "9.6"
                    then "notify"
                    else "simple";
 
@@ -352,5 +369,5 @@ in
   };
 
   meta.doc = ./postgresql.xml;
-  meta.maintainers = with lib.maintainers; [ thoughtpolice ];
+  meta.maintainers = with lib.maintainers; [ thoughtpolice danbst ];
 }

pkgs/servers/sql/postgresql/default.nix

@@ -175,6 +175,9 @@ let
       cp --target-directory=$out/bin ${postgresql}/bin/{postgres,pg_config,pg_ctl}
       wrapProgram $out/bin/postgres --set NIX_PGLIBDIR $out/lib
     '';
+
+    passthru.version = postgresql.version;
+    passthru.psqlSchema = postgresql.psqlSchema;
   };
 
 in self: {