Fix a union file system bug

TODO

@@ -1,4 +1,4 @@
-NuttX TODO List (Last updated June 22, 2015)
+NuttX TODO List (Last updated June 24, 2015)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 This file summarizes known NuttX bugs, limitations, inconsistencies with
@@ -19,7 +19,7 @@ nuttx/
  (12)  Network (net/, drivers/net)
   (5)  USB (drivers/usbdev, drivers/usbhost)
  (12)  Libraries (libc/, libm/)
- (12)  File system/Generic drivers (fs/, drivers/)
+ (11)  File system/Generic drivers (fs/, drivers/)
   (8)  Graphics subsystem (graphics/)
   (1)  Pascal add-on (pcode/)
   (2)  Build system / Toolchains
@@ -1439,24 +1439,6 @@ o File system / Generic drivers (fs/, drivers/)
                   ignored by readder() logic.  This the file does not
                   appear in the 'ls'.
 
-  Title:       UNIONFS WITH OFFSETS
-  Description: The Union File System supports offset strings to allow
-               directories to appear at an offset below the union mount
-               point.  These offsets work in many cases (open, close, read, 
-               write, etc.), but there are some problems:
-
-               1. The current test case at apps/examples/unionfs uses an
-                  offset string for one file system, but the offset string
-                  is matched by a a directory in the other file system.
-                  This causes many problems with the offset file system to
-                  be obscured.
-               2. If both contained file systems are offset, then stat(),
-                  opendir(), readdir() etc. fail.
-               3. The offsets do not work for directory operations on their
-                  the top level directory.
-  Status:      Open
-  Priority:    High-ish
-
 o Graphics subsystem (graphics/)
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

include/nuttx/fs/dirent.h

@@ -157,6 +157,8 @@ struct fs_dirent_s;                           /* Forward reference */
 struct fs_unionfsdir_s
 {
   uint8_t fu_ndx;                             /* Index of file system being enumerated */
+  bool fu_eod;                                /* True: At end of directory */
+  bool fu_prefix[2];                          /* True: Fake directory in prefix */
   FAR char *fu_relpath;                       /* Path being enumerated */
   FAR struct fs_dirent_s *fu_lower[2];        /* dirent struct used by contained file system */
 };