Add a cache for backstore lookups

For each new SO we need to verify there isn't an existing one with the
same (type, name). Unfortunately these are nested in directories, so
adding each new SO requires more directory searches. AFAIK there's no
way around this without changing configfs layout.

This change adds a backstore cache. We still resort to glob() for new
SOs (it's still O(n^2)) but avoiding this for SOs we've seen before really
seems to help a lot.

Signed-off-by: Andy Grover <agrover@redhat.com>

1 files changed, 19 insertions, 10 deletions

diff --git a/rtslib/tcm.py b/rtslib/tcm.py
index 7dbc1b9..b3fb374 100644
--- a/rtslib/tcm.py
+++ b/rtslib/tcm.py
@@ -713,6 +713,7 @@ bs_params = {
     BlockStorageObject: dict(name='block', alt_dirprefix='iblock'),
     }
 
+bs_cache = {}
 
 class _Backstore(CFSNode):
     """
@@ -721,27 +722,31 @@ class _Backstore(CFSNode):
     Created by storageobject ctor before SO configfs entry.
     """
 
-    def __init__(self, name, storage_object_cls, mode, index=None):
+    def __init__(self, name, storage_object_cls, mode):
         super(_Backstore, self).__init__()
         self._so_cls = storage_object_cls
         self._plugin = bs_params[self._so_cls]['name']
-        self._index = index
 
         dirp = bs_params[self._so_cls].get("alt_dirprefix", self._plugin)
 
-        # does (so_cls, index) exist already?
-        for plugin, num in self._hbas(self.path):
-            if os.path.isdir("%s/core/%s_%s/%s" %
-                             (self.path, dirp, num, name)):
+        # mapping in cache?
+        lookup_key = "%s/%s" % (dirp, name)
+        self._index = bs_cache.get(lookup_key, None)
+
+        if not self._index:
+            # cache miss. does (so_cls, index) exist already?
+            dirs = glob.glob("%s/core/%s_*/%s" % (self.configfs_dir, dirp, name))
+            if len(dirs):
                 if mode == 'create':
                     raise RTSLibError("Storage object %s/%s already exists" %
                                       (self._plugin, name))
                 else:
-                    self._index = int(num)
-                    break
+                    self._index = int(dirs[0].split("/")[-2].rsplit("_", 1)[1])
+            else:
+                self._index = self._next_hba_index(self.configfs_dir)
+            bs_cache[lookup_key] = self._index
 
-        if self._index == None:
-            self._index = self._next_hba_index(self.configfs_dir)
+        self.lookup_key = lookup_key
 
         self._path = "%s/core/%s_%d" % (self.configfs_dir,
                                         dirp,
@@ -768,6 +773,10 @@ class _Backstore(CFSNode):
                 if regex:
                     yield(regex.group(1), regex.group(3))
 
+    def delete(self):
+        super(_Backstore, self).delete()
+        del bs_cache[self.lookup_key]
+
     def _get_index(self):
         return self._index