[libvirt] [PATCH v3 2/7] util: vircgroup: improve controller detection

[Pavel Hrdina]

This affects only cgroups v2 where enabled controllers are not based on
available mount points but on the list provided in cgroup.controllers
file.  However, moving it will fill in placement as well, so it needs
to be freed together with mount point if we don't need that controller.

Before this patch we were assuming that all controllers available in
root cgroup where available in all other sub-cgroups which was wrong.

In order to fix it we need to move the cgroup controllers detection
after cgroup placement was prepared in order to build correct path for
cgroup.controllers file.

Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
---

Notes:
    Changes in v3:
        - Moving the detection after placement means we need to free it
          together with mount point if that controller is not required.

 src/util/vircgroup.c   | 32 ++++++++++++++++----------------
 src/util/vircgroupv1.c |  1 +
 src/util/vircgroupv2.c |  5 +++--
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index b7e5f03521..da506fc0b0 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -381,22 +381,6 @@ virCgroupDetect(virCgroupPtr group,
             return -1;
     }
 
-    for (i = 0; i < VIR_CGROUP_BACKEND_TYPE_LAST; i++) {
-        if (group->backends[i]) {
-            int rc = group->backends[i]->detectControllers(group, controllers, parent);
-            if (rc < 0)
-                return -1;
-            controllersAvailable |= rc;
-        }
-    }
-
-    /* Check that at least 1 controller is available */
-    if (controllersAvailable == 0) {
-        virReportSystemError(ENXIO, "%s",
-                             _("At least one cgroup controller is required"));
-        return -1;
-    }
-
     /* In some cases we can copy part of the placement info
      * based on the parent cgroup...
      */
@@ -421,6 +405,22 @@ 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, parent);
+            if (rc < 0)
+                return -1;
+            controllersAvailable |= rc;
+        }
+    }
+
+    /* Check that at least 1 controller is available */
+    if (controllersAvailable == 0) {
+        virReportSystemError(ENXIO, "%s",
+                             _("At least one cgroup controller is required"));
+        return -1;
+    }
+
     return 0;
 }
 
diff --git a/src/util/vircgroupv1.c b/src/util/vircgroupv1.c
index fb3e0b2d47..4231d8d6fa 100644
--- a/src/util/vircgroupv1.c
+++ b/src/util/vircgroupv1.c
@@ -464,6 +464,7 @@ virCgroupV1DetectControllers(virCgroupPtr group,
                     }
                 }
                 VIR_FREE(group->legacy[i].mountPoint);
+                VIR_FREE(group->legacy[i].placement);
             }
         }
     } else {
diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c
index 2d09d77a29..29b5806a01 100644
--- a/src/util/vircgroupv2.c
+++ b/src/util/vircgroupv2.c
@@ -250,8 +250,9 @@ virCgroupV2ParseControllersFile(virCgroupPtr group)
     char **contList = NULL;
     char **tmp;
 
-    if (virAsprintf(&contFile, "%s/cgroup.controllers",
-                    group->unified.mountPoint) < 0)
+    if (virAsprintf(&contFile, "%s%s/cgroup.controllers",
+                    group->unified.mountPoint,
+                    NULLSTR_EMPTY(group->unified.placement)) < 0)
         return -1;
 
     rc = virFileReadAll(contFile, 1024 * 1024, &contStr);
-- 
2.21.0