1 files changed, 91 insertions, 0 deletions
diff --git a/xlators/features/glupy/examples/negative.py b/xlators/features/glupy/examples/negative.py
new file mode 100644
index 00000000000..e7a4fc07ced
--- /dev/null
+++ b/xlators/features/glupy/examples/negative.py
@@ -0,0 +1,91 @@
+import sys
+from uuid import UUID
+from gluster.glupy import *
+
+# Negative-lookup-caching example.  If a file wasn't there the last time we
+# looked, it's probably still not there.  This translator keeps track of
+# those failed lookups for us, and returns ENOENT without needing to pass the
+# call any further for repeated requests.
+
+# If we were doing this for real, we'd need separate caches for each xlator
+# instance.  The easiest way to do this would be to have xlator.__init__
+# "register" each instance in a module-global dict, with the key as the C
+# translator address and the value as the xlator object itself.  For testing
+# and teaching, it's sufficient just to have one cache.  The keys are parent
+# GFIDs, and the entries are lists of names within that parent that we know
+# don't exist.
+cache = {}
+
+# TBD: we need a better way of handling per-request data (frame->local in C).
+dl.get_id.restype = c_long
+dl.get_id.argtypes = [ POINTER(call_frame_t) ]
+
+def uuid2str (gfid):
+    return str(UUID(''.join(map("{0:02x}".format, gfid))))
+
+class xlator (Translator):
+
+    def __init__ (self, c_this):
+        self.requests = {}
+        Translator.__init__(self,c_this)
+
+    def lookup_fop (self, frame, this, loc, xdata):
+        pargfid = uuid2str(loc.contents.pargfid)
+        print "lookup FOP: %s:%s" % (pargfid, loc.contents.name)
+        # Check the cache.
+        if cache.has_key(pargfid):
+            if loc.contents.name in cache[pargfid]:
+                print "short-circuiting for %s:%s" % (pargfid,
+                    loc.contents.name)
+                dl.unwind_lookup(frame,0,this,-1,2,None,None,None,None)
+                return 0
+        key = dl.get_id(frame)
+        self.requests[key] = (pargfid, loc.contents.name[:])
+        # TBD: get real child xl from init, pass it here
+        dl.wind_lookup(frame,POINTER(xlator_t)(),loc,xdata)
+        return 0
+
+    def lookup_cbk (self, frame, cookie, this, op_ret, op_errno, inode, buf,
+                    xdata, postparent):
+        print "lookup CBK: %d (%d)" % (op_ret, op_errno)
+        key = dl.get_id(frame)
+        pargfid, name = self.requests[key]
+        # Update the cache.
+        if op_ret == 0:
+            print "found %s, removing from cache" % name
+            if cache.has_key(pargfid):
+                cache[pargfid].discard(name)
+        elif op_errno == 2:    # ENOENT
+            print "failed to find %s, adding to cache" % name
+            if cache.has_key(pargfid):
+                cache[pargfid].add(name)
+            else:
+                cache[pargfid] = set([name])
+        del self.requests[key]
+        dl.unwind_lookup(frame,cookie,this,op_ret,op_errno,
+                         inode,buf,xdata,postparent)
+        return 0
+
+    def create_fop (self, frame, this, loc, flags, mode, umask, fd, xdata):
+        pargfid = uuid2str(loc.contents.pargfid)
+        print "create FOP: %s:%s" % (pargfid, loc.contents.name)
+        key = dl.get_id(frame)
+        self.requests[key] = (pargfid, loc.contents.name[:])
+        # TBD: get real child xl from init, pass it here
+        dl.wind_create(frame,POINTER(xlator_t)(),loc,flags,mode,umask,fd,xdata)
+        return 0
+
+    def create_cbk (self, frame, cookie, this, op_ret, op_errno, fd, inode,
+                    buf, preparent, postparent, xdata):
+        print "create CBK: %d (%d)" % (op_ret, op_errno)
+        key = dl.get_id(frame)
+        pargfid, name = self.requests[key]
+        # Update the cache.
+        if op_ret == 0:
+            print "created %s, removing from cache" % name
+            if cache.has_key(pargfid):
+                cache[pargfid].discard(name)
+        del self.requests[key]
+        dl.unwind_create(frame,cookie,this,op_ret,op_errno,fd,inode,buf,
+                         preparent,postparent,xdata)
+        return 0