util: vircgroup: pass parent cgroup into virCgroupDetectControllersCB

In cgroups v2 we don't have to detect available controllers every single
time if we are creating a new cgroup based on parent cgroup.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/util/vircgroup.c

@@ -383,7 +383,7 @@ virCgroupDetect(virCgroupPtr group,
 
     for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
         if (group->backends[i]) {
-            int rc = group->backends[i]->detectControllers(group, controllers);
+            int rc = group->backends[i]->detectControllers(group, controllers, parent);
             if (rc < 0)
                 return -1;
             controllersAvailable |= rc;

src/util/vircgroupbackend.h

@@ -95,7 +95,8 @@ typedef char *
 
 typedef int
 (*virCgroupDetectControllersCB)(virCgroupPtr group,
-                                int controllers);
+                                int controllers,
+                                virCgroupPtr parent);
 
 typedef bool
 (*virCgroupHasControllerCB)(virCgroupPtr cgroup,

src/util/vircgroupv1.c

@@ -420,7 +420,8 @@ virCgroupV1StealPlacement(virCgroupPtr group)
 
 static int
 virCgroupV1DetectControllers(virCgroupPtr group,
-                             int controllers)
+                             int controllers,
+                             virCgroupPtr parent ATTRIBUTE_UNUSED)
 {
     size_t i;
     size_t j;

src/util/vircgroupv2.c

@@ -285,16 +285,21 @@ virCgroupV2ParseControllersFile(virCgroupPtr group)
 
 static int
 virCgroupV2DetectControllers(virCgroupPtr group,
-                             int controllers)
+                             int controllers,
+                             virCgroupPtr parent)
 {
     size_t i;
 
+    if (parent) {
+        group->unified.controllers = parent->unified.controllers;
+    } else {
         if (virCgroupV2ParseControllersFile(group) < 0)
             return -1;
 
         /* In cgroup v2 there is no cpuacct controller, the cpu.stat file always
          * exists with usage stats. */
         group->unified.controllers |= 1 << VIR_CGROUP_CONTROLLER_CPUACCT;
+    }
 
     for (i = 0; i < VIR_CGROUP_CONTROLLER_LAST; i++)
         VIR_DEBUG("Controller '%s' present=%s",