Numorous changes. See below:

Numorous changes. See below:

  - ext4: ext4_trunc_inode now requires inode index instead of an
          existing inode_ref.
  - ext4: the support of removing directory recursively is temporarily
          dropped.
  - ext4: ext4_dir_rm temporarily relies on ext4_fs_truncate instead of
          ext4_trunc_inode to ensure directory inode not having 0
          length in case of power failure.

  - ext4_journal: connect transactions having reference to the same blocks
                  together.