lxc: Clean up namespace mounts

5f697f64e5 introduced a regression
when using lxc containers with qcow2 and qemu-nbd.

When removing the rootfs from the host namespace, it would
terminate the qemu-nbd process as well. This would cause
the kernel too oops under Ubuntu 13.04. Since the underlying
device thtat the libvirt_lxc process disapears.

To get around this we just clean up the host namespace if the
instance is powered-on. When the instance terminates it will
teardown the whole container.

This fixes LP: #1115786

Change-Id: I98bec2338cb455dbd277295ab36767149e05634c
Signed-off-by: Chuck Short <chuck.short@canonical.com>

nova/virt/disk/api.py

@@ -258,10 +258,16 @@ class _DiskImage(object):
         return bool(self._mounter)
 
     def umount(self):
-        """Unmount a disk image from the file system."""
+        """Umount a mount point from the filesystem."""
+        if self._mounter:
+            self._mounter.do_umount()
+            self._mounter = None
+
+    def teardown(self):
+        """Remove a disk image from the file system."""
         try:
             if self._mounter:
-                self._mounter.do_umount()
+                self._mounter.do_teardown()
                 self._mounter = None
         finally:
             if self._mkdir:
@@ -334,11 +340,24 @@ def teardown_container(container_dir):
     It will umount the container that is mounted,
     and delete any linked devices.
     """
+    try:
+        img = _DiskImage(image=None, mount_dir=container_dir)
+        img.teardown()
+    except Exception, exn:
+        LOG.exception(_('Failed to teardown ntainer filesystem: %s'), exn)
+
+
+def clean_lxc_namespace(container_dir):
+    """Clean up the container namespace rootfs mounting one spawned.
+
+    It will umount the mounted names that is mounted
+    but leave the linked deivces alone.
+    """
     try:
         img = _DiskImage(image=None, mount_dir=container_dir)
         img.umount()
     except Exception, exn:
-        LOG.exception(_('Failed to unmount container filesystem: %s'), exn)
+        LOG.exception(_('Failed to umount container filesystem: %s'), exn)
 
 
 def inject_data_into_fs(fs, key, net, metadata, admin_password, files,

nova/virt/disk/mount/api.py

@@ -218,6 +218,11 @@ class Mount(object):
         """Call the unmnt, unmap and unget operations."""
         if self.mounted:
             self.unmnt_dev()
+
+    def do_teardown(self):
+        """Call the umnt, unmap, and unget operations."""
+        if self.mounted:
+            self.unmnt_dev()
         if self.mapped:
             self.unmap_dev()
         if self.linked:

nova/virt/libvirt/driver.py

@@ -2052,8 +2052,12 @@ class LibvirtDriver(driver.ComputeDriver):
         # namespace and so there is no need to keep the container rootfs
         # mounted in the host namespace
         if CONF.libvirt_type == 'lxc':
+            state = self.get_info(instance)['state']
             container_dir = os.path.join(inst_path, 'rootfs')
-            disk.teardown_container(container_dir=container_dir)
+            if state == power_state.RUNNING:
+                disk.clean_lxc_namespace(container_dir=container_dir)
+            else:
+                disk.teardown_container(container_dir=container_dir)
 
         return domain