.

bigfile/_file_zodb.pyx

@@ -91,13 +91,26 @@ cdef public class _ZBigFile(BigFile) [object _ZBigFile, type _ZBigFile_Type]:
             pywfileh  = pywconn.open(zf.zself._p_oid)
             zf.wfileh = pywfileh.wfileh
 
-        # return XXX
+        # zf is ready to serve mmap requests via .wfileh
+        # return pycapsule with corresponding mmap methods.
+        #
+        # the capsule is not bound to particula _ZBigFile object because
+        # .mmap_* methods receive BigFile* argument which they upcaset to _ZBigFile.
+        return _ZBigFile_mmap_pycapsule
 
 
-# functions that we give to virtmem bigfile_ops .mmap*
+# _ZBigFile_mmap_pycapsule is pycapsule with functions that we give to
+# PyBigFile for virtmem .mmap* ops.
+cdef extern from "<wendelin/bigfile/file.h>" nogil:
+    struct bigfile_ops:
+        pass
 cdef extern from * nogil:
+    """
+    extern bigfile_ops ZBigFile_mmap_ops;
+    """
     const bigfile_ops ZBigFile_mmap_ops
-
+from cpython cimport PyCapsule_New
+cdef object _ZBigFile_mmap_pycapsule = PyCapsule_New(&ZBigFile_mmap_ops, "bigfile.blkmmaper", NULL)
 
 
 # pywconnOf establishes and returns (py) wcfs.Conn associated with zconn.