Add cache support to the LVMLogicalVolumeDevice class

This way LVMLogicalVolumeDevice can report whether they are cached, provide
information related to their cache and attach cache pool to themselves so that
they become cached.

blivet/devices/lvm.py

@@ -532,6 +532,7 @@ def __init__(self, name, parents=None, size=None, uuid=None, segType=None,
 
         self._metaDataSize = Size(0)
         self._internal_lvs = []
+        self._cache = None
 
     def _check_parents(self):
         """Check that this device has parents as expected"""
@@ -854,6 +855,28 @@ def removeInternalLV(self, int_lv):
                                                                                        self.name)
             raise ValueError(msg)
 
+    @property
+    def cached(self):
+        return bool(self.cache)
+
+    @property
+    def cache(self):
+        if self.exists and not self._cache:
+            # check if we have a cache pool internal LV
+            pool = None
+            for lv in self._internal_lvs:
+                if isinstance(lv, LVMCachePoolLogicalVolumeDevice):
+                    pool = lv
+
+            self._cache = LVMCache(self, size=pool.size, exists=True)
+
+        return self._cache
+
+    def attach_cache(self, cache_pool_lv):
+        blockdev.lvm.cache_attach(self.vg.name, self.lvname, cache_pool_lv.lvname)
+        self._cache = LVMCache(self, size=cache_pool_lv.size, exists=True)
+
+
 @add_metaclass(abc.ABCMeta)
 class LVMInternalLogicalVolumeDevice(LVMLogicalVolumeDevice):
     """Abstract base class for internal LVs