Fix previous commit && alot of backports from 3.15
F2FS: Upstream updates
f2fs: switch to iov_iter_alignment()
f2fs: check name_len of dir entry to prevent from deadloop
f2fs: avoid to access NULL pointer in issue_flush_thread
f2fs: introduce help function {create,destroy}_flush_cmd_control
f2fs: cleanup the needless return of f2fs_create_root_stats
f2fs: remove the unused stat_lock
f2fs: introduce help function {create,destroy}_flush_cmd_control && add iov_iter.c
F2FS: Upstream updates
f2fs: fix to put root inode in error path of fill_super
f2fs: avoid use invalid mapping of node_inode when evict meta inode
f2fs: support ->rename2()
f2fs: add f2fs_balance_fs for direct IO