Check data integrity and layout stability during defrag compacting
EXT4_IOC_MOVE_EXT swap extents between target and donor inode.
If ioctl was performed twice then inode's layout should not change.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>