[PATCH] qemu_driver: add virCgroupMounted

[Lai Jiangshan <laijs@xxxxxxxxxxxxxx>]

When wen mount any cgroup without "-o devices", we will fail to start vms:

# virsh start vm1
error: Failed to start domain vm1
error: Unable to deny all devices for vm1: No such file or directory

When wen mount any cgroup without "-o cpu", we will fail to get schedinfo:
# virsh schedinfo vm1
Scheduler      : posix
error: unable to get cpu shares tunable: No such file or directory

We should only use the cgroup controllers which are mounted on host.
So I add virCgroupMounted() for qemuCgroupControllerActive()

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 3b127d6..5885ad8 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -61,6 +61,7 @@ virConfWriteMem;
 # cgroup.h
 virCgroupForDomain;
 virCgroupForDriver;
+virCgroupMounted;
 virCgroupRemove;
 virCgroupFree;
 virCgroupAddTask;
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 16f34f7..f09d029 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -724,6 +724,8 @@ static int qemuCgroupControllerActive(struct qemud_driver *driver,
 {
     if (driver->cgroup == NULL)
         return 0;
+    if (!virCgroupMounted(driver->cgroup, controller))
+        return 0;
     if (driver->cgroupControllers & (1 << controller))
         return 1;
     return 0;
diff --git a/src/util/cgroup.c b/src/util/cgroup.c
index 7e887dc..8fac389 100644
--- a/src/util/cgroup.c
+++ b/src/util/cgroup.c
@@ -71,6 +71,17 @@ void virCgroupFree(virCgroupPtr *group)
     VIR_FREE(*group);
 }
 
+/**
+ * virCgroupMounted: query whether a cgroup subsystem is mounted or not
+ *
+ * @cgroup: The group structure to be queried
+ * @controller: cgroup subsystem id
+ */
+bool virCgroupMounted(virCgroupPtr cgroup, int controller)
+{
+	return !!cgroup->controllers[controller].mountPoint;
+}
+
 #if defined HAVE_MNTENT_H && defined HAVE_GETMNTENT_R
 /*
  * Process /proc/mounts figuring out what controllers are
diff --git a/src/util/cgroup.h b/src/util/cgroup.h
index b8f2d08..9e1c61f 100644
--- a/src/util/cgroup.h
+++ b/src/util/cgroup.h
@@ -83,5 +83,6 @@ int virCgroupGetFreezerState(virCgroupPtr group, char **state);
 int virCgroupRemove(virCgroupPtr group);
 
 void virCgroupFree(virCgroupPtr *group);
+bool virCgroupMounted(virCgroupPtr cgroup, int controller);
 
 #endif /* CGROUP_H */

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