Create function to automatically generate log companion services

examples/services-agnostic/s6-svscan.nix

@@ -1,5 +1,11 @@
 {createManagedProcess, s6, runtimeDir}:
-{instanceSuffix ? "", instanceName ? "s6-svscan${instanceSuffix}", scanDir ? "${runtimeDir}/service${instanceSuffix}"}:
+
+{ instanceSuffix ? ""
+, instanceName ? "s6-svscan${instanceSuffix}"
+, scanDir ? "${runtimeDir}/service${instanceSuffix}"
+, logUser ? "s6-log${instanceSuffix}"
+, logGroup ? "s6-log${instanceSuffix}"
+}:
 
 createManagedProcess {
   name = instanceName;
@@ -9,4 +15,22 @@ createManagedProcess {
   initialize = ''
     mkdir -p ${scanDir}
   '';
+
+  credentials = {
+    groups = {
+      "${logGroup}" = {};
+    };
+    users = {
+      "${logUser}" = {
+        group = logGroup;
+        description = "s6-log user";
+      };
+    };
+  };
+
+  overrides = {
+    sysvinit = {
+      runlevels = [ 3 4 5 ];
+    };
+  };
 }

nixproc/create-managed-process/s6-rc/create-log-service-for-longrun-service.nix

@@ -0,0 +1,37 @@
+{stdenv, execline, logDir, logDirUser, logDirGroup, forceDisableUserChange}:
+{name}:
+
+let
+  serviceName = "${name}-log";
+
+  util = import ./util.nix {
+    inherit (stdenv) lib;
+  };
+
+  serviceLogDir = "${logDir}/s6-log/${name}";
+
+  notificationFd = 3;
+in
+stdenv.mkDerivation {
+  name = serviceName;
+  buildCommand = ''
+    mkdir -p $out/etc/s6/sv/${serviceName}
+    cd $out/etc/s6/sv/${serviceName}
+  ''
+  + util.generateStringProperty { value = "longrun"; filename = "type"; }
+  + ''
+    cat > run <<EOF
+    #!${execline}/bin/execlineb -P
+
+    foreground { mkdir -p ${serviceLogDir} }
+    ${stdenv.lib.optionalString (!forceDisableUserChange) ''
+      foreground { chown -R ${logDirUser}:${logDirGroup} ${serviceLogDir} }
+      s6-setuidgid ${logDirUser}
+    ''}
+    exec -c s6-log -d${toString notificationFd} ${serviceLogDir}
+    EOF
+  ''
+  + util.generateStringProperty { value = "${name}-srv"; filename = "consumer-for"; }
+  + util.generateIntProperty { value = notificationFd; filename = "notification-fd"; }
+  + util.generateStringProperty { value = name; filename = "pipeline-name"; };
+}

nixproc/create-managed-process/s6-rc/create-longrun-service.nix

@@ -1,4 +1,4 @@
-{stdenv, createCredentials}:
+{stdenv, createCredentials, createLogServiceForLongRunService}:
 
 { name
 # When a service is flagged as essential it will not stop with the command: s6-rc -d change foo, but only: s6-rc -D change foo
@@ -33,6 +33,8 @@
 # named with the content of the pipeline-name file, and containing all the services in the pipeline that ends at service.
 # The pipeline-name file is ignored if service is not a last consumer.
 , pipelineName ? null
+# Automatically generates a logging longrun service that writes the output to a log file
+, autoGenerateLogService ? true
 # Specifies which groups and users that need to be created.
 , credentials ? {}
 # Arbitrary commands executed after generating the configuration files
@@ -45,12 +47,21 @@ let
   util = import ./util.nix {
     inherit (stdenv) lib;
   };
+
+  logService = createLogServiceForLongRunService {
+    inherit name;
+  };
+
+  _producerFor = if autoGenerateLogService then logService else producerFor;
+
+  # The service name gets a -srv suffix so that it can be paired with a -log service and put in a bundle that corresponds to: name
+  serviceName = if autoGenerateLogService then "${name}-srv" else name;
 in
 stdenv.mkDerivation {
-  inherit name;
+  name = serviceName;
   buildCommand = ''
-    mkdir -p $out/etc/s6/sv/${name}
-    cd $out/etc/s6/sv/${name}
+    mkdir -p $out/etc/s6/sv/${serviceName}
+    cd $out/etc/s6/sv/${serviceName}
   ''
   + util.generateStringProperty { value = "longrun"; filename = "type"; }
   + util.generateBooleanProperty { value = flagEssential; filename = "flag-essential"; }
@@ -65,9 +76,13 @@ stdenv.mkDerivation {
   + util.generateStringProperty { value = downSignal; filename = "down-signal"; }
   + util.copyDir { path = data; filename = "data"; }
   + util.copyDir { path = env; filename = "env"; }
-  + util.generateServiceName { service = producerFor; filename = "producer-for"; }
+  + util.generateServiceName { service = _producerFor; filename = "producer-for"; }
   + util.generateServiceNameList { services = consumerFor; filename = "consumer-for"; }
   + util.generateStringProperty { value = pipelineName; filename = "pipeline-name"; }
+  + stdenv.lib.optionalString autoGenerateLogService ''
+    cd ..
+    ln -sfn ${logService}/etc/s6/sv/${name}-log
+  ''
   + ''
     ln -s ${credentialsSpec}/dysnomia-support $out/dysnomia-support
 

nixproc/create-managed-process/s6-rc/default.nix

@@ -1,8 +1,11 @@
-{stdenv, createCredentials}:
+{stdenv, execline, createCredentials, logDir, logDirUser ? "s6-log", logDirGroup ? "s6-log", forceDisableUserChange}:
 
-{
+rec {
+  createLogServiceForLongRunService = import ./create-log-service-for-longrun-service.nix {
+    inherit stdenv execline logDir logDirUser logDirGroup forceDisableUserChange;
+  };
   createLongRunService = import ./create-longrun-service.nix {
-    inherit stdenv createCredentials;
+    inherit stdenv createCredentials createLogServiceForLongRunService;
   };
   createOneShotService = import ./create-oneshot-service.nix {
     inherit stdenv createCredentials;

nixproc/create-managed-process/s6-rc/generate-s6-service.nix

@@ -88,6 +88,10 @@ let
   ''
   + stdenv.lib.optionalString (nice != null) ''
     nice -n ${toString nice}
+  ''
+  # Always forward standard error so that it can be captured by the s6-log service
+  + ''
+    fdmove -c 2 1
   '';
 
   escapeArgs = args:

nixproc/create-managed-process/universal/create-managed-process-universal.nix

@@ -104,8 +104,8 @@ let
   };
 
   s6-rc = import ../s6-rc {
-    inherit (pkgs) stdenv;
-    inherit createCredentials;
+    inherit (pkgs) stdenv execline;
+    inherit createCredentials logDir forceDisableUserChange;
   };
 
   generateS6Service = import ../s6-rc/generate-s6-service.nix {