We found strange blocks layout in our mail server, after careful study,
we got the reason and tried to fix it.
When loading an inode from buffer/disk(ext2/3_read_inode),then allocating the second block(block==1) of the corresponding file: i_next_alloc_block and i_next_alloc_goal are both zero,and in fact are not valid,
but they(i_next_alloc_block/goal) take effect in the former codes. This causes non-contiguous file.
Below patch add a check,and fixes this.