[PATCH 2/9] vircgroup: add assertion to allow cgroup controllers to stay empty

[Henning Schild <henning.schild@xxxxxxxxxxx>]

When using a hierarchy of cgroups we might want to add tasks just to
the children cgroups but never to the parent. To make sure we do not
use a parent cgroup by accident add a mechanism that lets us assert
a correct implementation in cases we want such a hierarchy.

i.e. for qemu cpusets we want all tasks in /vcpuX or /emulator, not
in /.

Signed-off-by: Henning Schild <henning.schild@xxxxxxxxxxx>
---
 src/libvirt_private.syms |  2 ++
 src/util/vircgroup.c     | 19 +++++++++++++++++++
 src/util/vircgroup.h     |  3 +++
 src/util/vircgrouppriv.h |  1 +
 4 files changed, 25 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 83f6e2c..cf93d06 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1201,6 +1201,7 @@ virCgroupDenyDeviceMajor;
 virCgroupDenyDevicePath;
 virCgroupDetectMountsFromFile;
 virCgroupFree;
+virCgroupGetAssertEmpty;
 virCgroupGetBlkioDeviceReadBps;
 virCgroupGetBlkioDeviceReadIops;
 virCgroupGetBlkioDeviceWeight;
@@ -1245,6 +1246,7 @@ virCgroupNewThread;
 virCgroupPathOfController;
 virCgroupRemove;
 virCgroupRemoveRecursively;
+virCgroupSetAssertEmpty;
 virCgroupSetBlkioDeviceReadBps;
 virCgroupSetBlkioDeviceReadIops;
 virCgroupSetBlkioDeviceWeight;
diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
index 0b65238..ad46dfc 100644
--- a/src/util/vircgroup.c
+++ b/src/util/vircgroup.c
@@ -1197,6 +1197,15 @@ virCgroupAddTaskController(virCgroupPtr group, pid_t pid, int controller)
         return -1;
     }
 
+    if(group->assert_empty & (1 << controller)) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("Controller '%s' is not supposed to contain any"
+                         " tasks. group=%s pid=%d\n"),
+                       virCgroupControllerTypeToString(controller),
+                       group->path, pid);
+        return -1;
+    }
+
     return virCgroupSetValueU64(group, controller, "tasks",
                                 (unsigned long long)pid);
 }
@@ -1246,6 +1255,16 @@ virCgroupAddTaskStrController(virCgroupPtr group,
     return rc;
 }
 
+void
+virCgroupSetAssertEmpty(virCgroupPtr group, int mask) {
+    group->assert_empty = mask;
+}
+
+int
+virCgroupGetAssertEmpty(virCgroupPtr group) {
+    return group->assert_empty;
+}
+
 
 /**
  * virCgroupMoveTask:
diff --git a/src/util/vircgroup.h b/src/util/vircgroup.h
index 63a9e1c..f244c24 100644
--- a/src/util/vircgroup.h
+++ b/src/util/vircgroup.h
@@ -131,6 +131,9 @@ int virCgroupAddTaskController(virCgroupPtr group,
                                pid_t pid,
                                int controller);
 
+void virCgroupSetAssertEmpty(virCgroupPtr group, int mask);
+int virCgroupGetAssertEmpty(virCgroupPtr group);
+
 int virCgroupMoveTask(virCgroupPtr src_group,
                       virCgroupPtr dest_group);
 
diff --git a/src/util/vircgrouppriv.h b/src/util/vircgrouppriv.h
index 722863e..944d6ae 100644
--- a/src/util/vircgrouppriv.h
+++ b/src/util/vircgrouppriv.h
@@ -44,6 +44,7 @@ struct virCgroupController {
 
 struct virCgroup {
     char *path;
+    int assert_empty;
 
     struct virCgroupController controllers[VIR_CGROUP_CONTROLLER_LAST];
 };
-- 
2.4.10

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