* Add a module for managing cgroups.

svn path=/nixos/trunk/; revision=30551

modules/module-list.nix

@@ -146,6 +146,7 @@
   ./services/scheduling/fcron.nix
   ./services/security/tor.nix
   ./services/security/torsocks.nix
+  ./services/system/cgroups.nix
   ./services/system/dbus.nix
   ./services/system/kerberos.nix
   ./services/system/nscd.nix

modules/services/system/cgroups.nix

@@ -0,0 +1,140 @@
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let
+
+  cfg = config.services.cgroups;
+
+  cgconfigConf = pkgs.writeText "cgconfig.conf" cfg.groups;
+
+  cgrulesConf = pkgs.writeText "cgrules.conf" cfg.rules;
+
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    services.cgroups.enable = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Whether to enable support for control groups, a Linux kernel
+        feature for resource management.  It allows you to assign
+        processes to groups that share certain resource limits (e.g.,
+        CPU or memory).  The <command>cgrulesengd</command> daemon
+        automatically assigns processes to the right cgroup depending
+        on the rules defined in
+        <option>services.cgroups.rules</option>.
+      '';
+    };
+
+    services.cgroups.groups = mkOption {
+      type = types.string;
+      default =
+        ''
+          mount {
+            cpu = /dev/cgroup/cpu;
+          }
+        '';
+      example =
+        ''
+          mount {
+            cpu = /dev/cgroup/cpu;
+            cpuacct = /dev/cgroup/cpuacct;
+          }
+
+          # Create a "www" cgroup with a lower share of the CPU (the
+          # default is 1024).
+          group www {
+            cpu {
+              cpu.shares = "500";
+            }
+          }
+        '';
+      description = ''
+        The contents of the <filename>cgconfig.conf</filename>
+        configuration file, which defines the cgroups.
+      '';
+    };
+
+    services.cgroups.rules = mkOption {
+      type = types.string;
+      default = "";
+      example =
+        ''
+          # All processes executed by the "wwwrun" uid should be
+          # assigned to the "www" CPU cgroup.
+          wwwrun cpu www
+        '';
+      description = ''
+        The contents of the <filename>cgrules.conf</filename>
+        configuration file, which determines to which cgroups
+        processes should be assigned by the
+        <command>cgrulesengd</command> daemon.
+      '';
+    };
+
+  };
+
+  
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    environment.systemPackages = [ pkgs.libcgroup ];
+
+    environment.etc =
+      [ { source = cgconfigConf;
+          target = "cgconfig.conf";
+        }
+        { source = cgrulesConf;
+          target = "cgrules.conf";
+        }
+      ];
+
+    jobs.cgroups =
+      { startOn = "startup";
+
+        description = "Control groups daemon";
+
+        path = [ pkgs.libcgroup pkgs.procps ];
+      
+        preStart =
+          ''
+            # The daemon requires the userspace<->kernelspace netlink
+            # connector.
+            ${config.system.sbin.modprobe}/sbin/modprobe cn || true
+          
+            cgclear || true
+
+            # Mount the cgroup hierarchies.  Note: we refer to the
+            # store path of cgconfig.conf here to ensure that the job
+            # gets reloaded if the configuration changes.
+            cgconfigparser -l ${cgconfigConf}
+
+            # Move existing processes to the right cgroup.
+            cgclassify --cancel-sticky $(ps --no-headers -eL o tid) || true
+
+            # Force a restart if the rules change:
+            # ${cgrulesConf}
+          '';
+
+        # Run the daemon that moves new processes to the right cgroup.
+        exec = "cgrulesengd";
+
+        daemonType = "fork";
+
+        postStop =
+          ''
+            cgclear
+          '';
+      };
+      
+
+  };
+
+}

modules/system/activation/activation-script.nix

@@ -129,14 +129,6 @@ in
         mkdir -p /media
       '';
 
-    system.activationScripts.cgroups =
-      ''
-        if ! ${pkgs.sysvtools}/bin/mountpoint -q /dev/cgroup; then
-            mkdir -p /dev/cgroup
-            ${pkgs.utillinux}/bin/mount -t cgroup -o freezer,cpuacct,cpu,cpuset none /dev/cgroup
-        fi
-      '';
-
   };
 
 }