Remove the SystemdCgroup feature

src/libstore/build/local-derivation-goal.cc

@@ -495,9 +495,6 @@ void LocalDerivationGoal::startBuilder()
         }
     }
 
-    useSystemdCgroup = parsedDrv->getRequiredSystemFeatures().count("Systemd-cgroup");
-    assert(!useSystemdCgroup);
-
     if (useChroot) {
 
         /* Allow a user-configurable set of directories from the
@@ -649,20 +646,18 @@ void LocalDerivationGoal::startBuilder()
                 dirsInChroot.erase(worker.store.printStorePath(*i.second.second));
         }
 
-        if (useSystemdCgroup) {
-            settings.requireExperimentalFeature(Xp::SystemdCgroup);
-            std::optional<Path> cgroup;
-            if (!buildUser || !(cgroup = buildUser->getCgroup()))
-                throw Error("feature 'systemd-cgroup' requires 'auto-allocate-uids = true' in nix.conf");
+        if (buildUser) {
+            if (auto cgroup = buildUser->getCgroup()) {
                 chownToBuilder(*cgroup);
                 chownToBuilder(*cgroup + "/cgroup.procs");
+                chownToBuilder(*cgroup + "/cgroup.threads");
+                //chownToBuilder(*cgroup + "/cgroup.subtree_control");
+            }
         }
 
 #else
         if (parsedDrv->useUidRange())
             throw Error("feature 'uid-range' is not supported on this platform");
-        if (useSystemdCgroup)
-            throw Error("feature 'systemd-cgroup' is not supported on this platform");
         #if __APPLE__
             /* We don't really have any parent prep work to do (yet?)
                All work happens in the child, instead. */
@@ -673,8 +668,6 @@ void LocalDerivationGoal::startBuilder()
     } else {
         if (parsedDrv->useUidRange())
             throw Error("feature 'uid-range' is only supported in sandboxed builds");
-        if (useSystemdCgroup)
-            throw Error("feature 'systemd-cgroup' is only supported in sandboxed builds");
     }
 
     if (needsHashRewrite() && pathExists(homeDir))
@@ -1845,7 +1838,7 @@ void LocalDerivationGoal::runChild()
             /* Unshare the cgroup namespace. This means
                /proc/self/cgroup will show the child's cgroup as '/'
                rather than whatever it is in the parent. */
-            if (useSystemdCgroup && unshare(CLONE_NEWCGROUP) == -1)
+            if (buildUser && buildUser->getUIDCount() != 1 && unshare(CLONE_NEWCGROUP) == -1)
                 throw SysError("unsharing cgroup namespace");
 
             /* Do the chroot(). */

src/libstore/build/local-derivation-goal.hh

@@ -41,10 +41,6 @@ struct LocalDerivationGoal : public DerivationGoal
 
     Path chrootRootDir;
 
-    /* Whether to make the 'systemd' cgroup controller available to
-       the build. */
-    bool useSystemdCgroup = false;
-
     /* RAII object to delete the chroot directory. */
     std::shared_ptr<AutoDelete> autoDelChroot;
 

src/libutil/experimental-features.cc

@@ -15,7 +15,6 @@ std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
     { Xp::FetchClosure, "fetch-closure" },
     { Xp::ReplFlake, "repl-flake" },
     { Xp::AutoAllocateUids, "auto-allocate-uids" },
-    { Xp::SystemdCgroup, "systemd-cgroup" },
 };
 
 const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)

src/libutil/experimental-features.hh

@@ -24,7 +24,6 @@ enum struct ExperimentalFeature
     FetchClosure,
     ReplFlake,
     AutoAllocateUids,
-    SystemdCgroup,
 };
 
 /**