.

wcfs/__init__.py

@@ -108,9 +108,11 @@ class _Mapping(object):
     # .file         _File
     # .blk_start    offset of this mapping in file
     # .mem          mmaped memory
-    pass
 
-    # XXX property .blk_stop = blk_start + len(mem) // blksize      & assert len(mem) % blksize == 0
+    @property
+    def blk_stop(mmap):
+        assert len(mmap.mem) % mmap.file.blksize == 0
+        return mmap.blk_start + len(mmap.mem) // mmap.file.blksize
 
 
 # connect creates new Conn viewing WCFS state as of @at.

wcfs/wcfs_test.py

@@ -1704,9 +1704,13 @@ def test_wcfspy_virtmem():
     wconn = t.wc.connect(at1)
     defer(wconn.close)
 
-    m1 = wconn.mmap(zf._p_oid, 2, 2)
+    m1 = wconn.mmap(zf._p_oid, 2, 3)
     defer(m1.unmap)
 
+    assert m1.blk_start == 2
+    assert m1.blk_stop  == 5
+    assert len(m1.mem)  == 3*zf.blksize
+
 
 # ---- misc ---