[PATCH-next 02/40] lnst.Devices.RemoteDevice: add caching capability

From: Ondrej Lichtner <olichtne(a)redhat.com&gt;

RemoteDevice objects that on the Controller act as proxies for the real
Device objects on Slaves can now be switched into a cached read only
mode.

In this mode, the RemoteDevice object stores all the property values of
the Slave Device locally on the Controller. When the tester attempts to
access a property this cached value is returned and no proxy call to the
Slave happens.

Method calls and setting new values to a property is disabled as this is
a read only mode. Unfortunatelly this means that methods that don't
change the device state (e.g. ips_filter) are also unaccessible.
However it also means that the cached RemoteDevice object can be used
even if the Device doesn't exist on the Slave anymore.

Signed-off-by: Ondrej Lichtner <olichtne(a)redhat.com&gt;
---
 lnst/Devices/RemoteDevice.py | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/lnst/Devices/RemoteDevice.py b/lnst/Devices/RemoteDevice.py
index ddd47f1..8a3f0cf 100644
--- a/lnst/Devices/RemoteDevice.py
+++ b/lnst/Devices/RemoteDevice.py
@@ -13,7 +13,7 @@ olichtne(a)redhat.com (Ondrej Lichtner)
 
 from copy import deepcopy
 from lnst.Devices.Device import Device
-from lnst.Common.DeviceError import DeviceDeleted
+from lnst.Common.DeviceError import DeviceDeleted, DeviceReadOnly
 
 def remotedev_decorator(cls):
     def func(*args, **kwargs):
@@ -36,6 +36,10 @@ class RemoteDevice(object):
         self._machine = None
         self.ifindex = None
         self.deleted = False
+
+        self._cache = {}
+        self._cached = False
+
         self._inited = True
 
     def __deepcopy__(self, memo):
@@ -49,6 +53,20 @@ class RemoteDevice(object):
         newone._inited = deepcopy(self._inited, memo)
         return newone
 
+    def enable_readonly_cache(self):
+        self._cache = {}
+        for name, val in self:
+            self._cache[name] = val
+        self._cached = True
+
+    def disable_readonly_cache(self):
+        self._cache = {}
+        self._cached = False
+
+    def update_readonly_cache(self):
+        self.disable_readonly_cache()
+        self.enable_readonly_cache()
+
     @property
     def _dev_cls(self):
         return self.__dev_cls
@@ -85,16 +103,22 @@ class RemoteDevice(object):
 
         attr = getattr(self._dev_cls, name)
 
-        if self.deleted:
+        if self.deleted and not self._cached:
             raise DeviceDeleted("This device was deleted on the slave and does not
exist anymore.")
 
         if callable(attr):
+            if self._cached:
+                raise DeviceReadOnly("Can't call methods when in ReadOnly cache
mode.")
+
             def dev_method(*args, **kwargs):
                 return self._machine.rpc_call("dev_method", self.ifindex,
                                               name, args, kwargs,
                                               netns=self.netns)
             return dev_method
         else:
+            if self._cached:
+                return self._cache[name]
+
             return self._machine.rpc_call("dev_attr", self.ifindex, name,
                                           netns=self.netns)
 
@@ -104,6 +128,10 @@ class RemoteDevice(object):
 
         try:
             getattr(self._dev_cls, name)
+
+            if self._cached:
+                raise DeviceReadOnly("Can't set attributes when in ReadOnly
cache mode.")
+
             return self._machine.rpc_call("dev_set_attr", self.ifindex, name,
value,
                                           netns=self.netns)
         except AttributeError:
-- 
2.17.0