多重 ecryptfs 加密可能吗？

Question

多重 ecryptfs 加密可能吗？

如何加密名为level2的已安装文件夹ecryptfs内的名为的文件夹？ecryptfslevel1

level1和level2文件夹的组织方式为

# tree
/root/    
  └─level1
    └─level2 

level1 使用 ecryptfs 加密：

# mount -t ecryptfs /root/level1 /root/level1

但是我无法安装level2文件夹

# mount -t ecryptfs level2 
Passphrase: 
Filename Encryption Key (FNEK) Signature [d3f92227db598fd6]: 
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_fnek_sig=d3f92227db598fd6
  ecryptfs_passthrough
  ecryptfs_key_bytes=32
  ecryptfs_cipher=aes
  ecryptfs_sig=d3f92227db598fd6
mount: wrong fs type, bad option, bad superblock on /root/level1/level2,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
Error mounting eCryptfs: [-1] Operation not permitted
Check your system logs; visit <http://ecryptfs.org/support.html>

和 dmesg |尾巴给我

[...]
[36057.561958] Mount on filesystem of type eCryptfs explicitly disallowed due to known incompatibilities
[36057.562176] Reading sb failed; rc = [-22]

PS：我只对ecryptfs加密感兴趣。请不要建议我使用EncFS（它适用于多重加密，但不是安全的加密系统）或全分区加密。