[Kimchi-devel] [PATCH] host/partitions: avoid calling disks.get_partitions_names() for each partition

[Zhou Zheng Sheng]

In PartitionModel.lookup(), it calls disks.get_partitions_names() to
verify the given partition is eligible to be used in a new logical
storage pool as follow.
  if name not in disks.get_partitions_names():
      raise NotFoundError(...)

When the front-end issues GET request to host/partitions, the back-end
would call get_partitions_names() for each partition. If there are many
disks and partitions in the host, get_partitions_names() takes a long
time to finish, and calling get_partitions_names() for each partition
would make the GET request timeout.

This patch is to do the following.
  When the partition is listed from the URI host/partitions, we should
avoid calling get_partitions_names() for each of them.
  When the partition is listed from the URI host/partitions/sdaX, we
should verify sdaX is among the eligible partitions.

The solution is that we make use of the resource_args in Partitions
collection class and override the _get_resources() method. In the
_get_resources() method, it sets resource_args to "[True]", indicating
that the listed partitions are already verified and eligible, so
PartitionModel.lookup() would skip the check. When we are outside of
_get_resources() method, resource_args is set to "[False]", and
PartitionModel.lookup() enables the check.

Signed-off-by: Zhou Zheng Sheng <zhshzhou at linux.vnet.ibm.com>
---
 src/kimchi/control/host.py | 26 +++++++++++++++++++++-----
 src/kimchi/model/host.py   |  4 ++--
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/src/kimchi/control/host.py b/src/kimchi/control/host.py
index ad34919..11673d5 100644
--- a/src/kimchi/control/host.py
+++ b/src/kimchi/control/host.py
@@ -17,11 +17,14 @@
 # License along with this library; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
 
+import threading
+
 import cherrypy
 
 from kimchi.control.base import Collection, Resource, SimpleCollection
 from kimchi.control.utils import UrlSubNode, validate_method
 from kimchi.exception import OperationFailed
+from kimchi.rollbackcontext import RollbackContext
 from kimchi.template import render
 
 
@@ -75,18 +78,31 @@ class Partitions(Collection):
     def __init__(self, model):
         super(Partitions, self).__init__(model)
         self.resource = Partition
+        self._reset_resource_args()
+        self._resource_args_lock = threading.Lock()
+
+    def _reset_resource_args(self):
+        self.resource_args = [False]
 
-    # Defining get_resources in order to return list of partitions in UI
-    # sorted by their path
     def _get_resources(self, flag_filter):
-        res_list = super(Partitions, self)._get_resources(flag_filter)
-        res_list.sort(key=lambda x: x.info['path'])
+        with RollbackContext() as rollback:
+            self._resource_args_lock.acquire()
+            rollback.prependDefer(self._resource_args_lock.release)
+
+            self.resource_args = [True]
+            rollback.prependDefer(self._reset_resource_args)
+
+            # Defining get_resources in order to return list of partitions in
+            # UI sorted by their path
+            res_list = super(Partitions, self)._get_resources(flag_filter)
+            res_list.sort(key=lambda x: x.info['path'])
         return res_list
 
 
 class Partition(Resource):
-    def __init__(self, model, id):
+    def __init__(self, model, verified, id):
         super(Partition, self).__init__(model, id)
+        self.model_args = [verified] + list(self.model_args)
 
     @property
     def data(self):
diff --git a/src/kimchi/model/host.py b/src/kimchi/model/host.py
index 47b0aa1..ebd6f79 100644
--- a/src/kimchi/model/host.py
+++ b/src/kimchi/model/host.py
@@ -244,8 +244,8 @@ class PartitionModel(object):
     def __init__(self, **kargs):
         pass
 
-    def lookup(self, name):
-        if name not in disks.get_partitions_names():
+    def lookup(self, verified, name):
+        if not verified and name not in disks.get_partitions_names():
             raise NotFoundError("KCHPART0001E", {'name': name})
 
         return disks.get_partition_details(name)
-- 
1.9.0